UNIMARK GROUP INC
SC 13D, 1998-02-27
CANNED, FRUITS, VEG, PRESERVES, JAMS & JELLIES
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<PAGE>   1





                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549

                                  SCHEDULE 13D

                   Under the Securities Exchange Act of 1934

                            THE UNIMARK GROUP, INC.
                                (Name of Issuer)


                     Common Stock, par value $.01 per share
                         (Title of Class of Securities)


                                  904789 10 4

                                 (CUSIP Number)


                              Rafael Vaquero Bazan
                               The UniMark House
                                  P.O. Box 229
                              Argyle, Texas 76226
                                 (817) 491-2992
                 (Name, Address and Telephone Number of Person
               Authorized to Receive Notices and Communications)


                               February 18, 1998
                      (Date of Event which Requires Filing
                               of this Statement)

If the person has previously filed a statement on Schedule 13G to report the
acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box [ ].

Check the following box if a fee is being paid with this Statement [X].

NOTE: Six copies of this statement, including all exhibits, should be filed
with the Commission. See Rule 13d-a(a) for other parties to whom copies are to
be sent.

The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).
<PAGE>   2
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                    PAGE 2 OF 12
                                                    Filed Pursuant to Rule 13D-1

<TABLE>
<S>                                                                                            <C>
(1)      NAME OF REPORTING PERSON                                                              Asesoria Garza Jasso, S.C.
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                         (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                   (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                                00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                               [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                    Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                              0
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                   500,000
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                         0
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                              500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                    500,000 (1)
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                       [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                            5.8%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                    CO
</TABLE>

______________________________________
(1)      Each of the Scheduled Persons listed in Annex 1 hereto share voting
         and investment power with respect to the shares owned by Asesoria
         Garza Jasso, S.C.
<PAGE>   3
                                 SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                   PAGE 3 OF 12
                                                   Filed Pursuant to Rule 13D-1


<TABLE>
<S>                                                                                                  <C>
(1)      NAME OF REPORTING PERSON                                                                    Rafael Vaquero Bazan
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                         (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                   (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                               00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                               [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                   Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                       226,236
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                  500,000 (2)
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                  226,236
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                             500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                   726,236
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                       [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                           8.4%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                   IN
</TABLE>

_______________________________________
(2)      Mr. R. Vaquero shares voting and investment power with each of the
         Scheduled Persons listed in Annex 1 as attached hereto with respect to
         the shares owned by Asesoria Garza Jasso, S.C.
<PAGE>   4
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 4 OF 12
                          Filed Pursuant to Rule 13D-1


<TABLE>
<S>                                                                                                 <C>
(1)      NAME OF REPORTING PERSON                                                                   Eduardo Vaquero Bazan
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                           (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                     (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                                  00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                                 [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                      Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                           42,981
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                 500,000 (3)
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                      42,981
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                                500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                      542,981
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                         [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                             6.3%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                      IN
</TABLE>

- --------------------------------
(3)      Mr. E. Vaquero shares voting and investment power with each of the
         Scheduled Persons listed in Annex 1 as attached hereto with respect to
         the shares owned by Asesoria Garza Jasso, S.C.
<PAGE>   5
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 5 OF 12
                          Filed Pursuant to Rule 13D-1


<TABLE>
<S>                                                                                                  <C>
(1)      NAME OF REPORTING PERSON                                                                    Pedro Vaquero Garcia
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                           (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                     (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                                  00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                                 [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                      Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                           63,000
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                 500,000 (4)
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                      63,000
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                                500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                      563,000
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                        [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                             6.5%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                      IN
</TABLE>

- ---------------------------------
(4)      Mr. P. Vaquero shares voting and investment power with each of the
         Scheduled Persons listed in Annex 1 as attached hereto with respect to
         the shares owned by Asesoria Garza Jasso, S.C.
<PAGE>   6
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 6 OF 12
                          Filed Pursuant to Rule 13D-1


<TABLE>
<S>                                                                                                <C>
(1)      NAME OF REPORTING PERSON                                                                  Fernando Camacho Casas
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                           (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                     (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                                  00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                                 [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                      Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                          206,565
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                 500,000 (5)
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                     206,565
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                                500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                      706,565
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                        [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                            8.2%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                      IN
</TABLE>

- ----------------------------
(5)      Mr. Camacho shares voting and investment power with each of the
         Scheduled Persons listed in Annex 1 as attached hereto with respect to
         the shares owned by Asesoria Garza Jasso, S.C.
<PAGE>   7
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 7 OF 12
                          Filed Pursuant to Rule 13D-1


<TABLE>
<S>                                                                                                  <C>
(1)      NAME OF REPORTING PERSON                                                                    Jose Martinez Brohez
         S.S. OR I.R.S. IDENTIFICATION
         NO. OF ABOVE PERSON

(2)      CHECK THE APPROPRIATE BOX IF A                                                                           (a) [ ]
         MEMBER OF A GROUP (SEE INSTRUCTIONS)                                                                     (b) [X]

(3)      SEC USE ONLY

(4)      SOURCE OF FUNDS (SEE ITEM 3)                                                                                  00

(5)      CHECK IF DISCLOSURE OF LEGAL                                                                                 [ ]
         PROCEEDINGS IS REQUIRED PURSUANT
         TO ITEMS 2(D) OR 2(E)

(6)      CITIZENSHIP OR PLACE OF ORGANIZATION                                                                      Mexico

NUMBER OF        (7)      SOLE VOTING POWER (SEE ITEM 5)                                                           46,800
SHARES
BENEFICIALLY     (8)      SHARED VOTING POWER                                                                 500,000 (6)
OWNED BY
EACH             (9)      SOLE DISPOSITIVE POWER (SEE ITEM 5)                                                      46,800
REPORTING
PERSON           (10)     SHARED DISPOSITIVE POWER                                                                500,000


(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED                                                                      546,800
         BY EACH REPORTING PERSON (SEE ITEM 5)

(12)     CHECK IF THE AGGREGATE AMOUNT IN ROW                                                                         [X]
         (11) EXCLUDES CERTAIN SHARES

(13)     PERCENT OF CLASS REPRESENTED BY                                                                            6.36%
         AMOUNT IN ROW (11)

(14)     TYPE OF REPORTING PERSON                                                                                      IN
</TABLE>

- ---------------------------------------
(6)      Mr. Brohez shares voting and investment power with each of the
         Scheduled Persons listed in Annex 1 as attached hereto with respect to
         the shares owned by Asesoria Garza Jasso, S.C.
<PAGE>   8
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 8 OF 12
                          Filed Pursuant to Rule 13D-1


ITEM 1.  SECURITY AND ISSUER

         This Statement relates to the common stock, $.01 par value per share,
         of The UniMark Group, Inc., a Texas corporation.  Its principal
         executive offices are located at UniMark House, Bartonville, Texas
         76226.


ITEM 2.  IDENTITY AND BACKGROUND

         (a-c) This Statement is filed by Asesoria Garza Jasso, S.C., a Mexican
         corporation ("Asesoria"), Rafael Vaquero Bazan, Eduardo Vaquero Bazan,
         Pedro Vaquero Garcia, Fernando Camacho Casas and Jose Martinez
         Brohez..  The principal office address of Asesoria is 124 McMakin
         Road, Bartonville, Texas 76226.  The name, address, citizenship and
         present principal occupation or employment of each executive officer,
         director and each person controlling Asesoria (collectively, the
         "Scheduled Persons") are set forth in Annex 1 attached hereto, and
         incorporated herein by reference.

         Asesoria is a privately held Mexican investment fund that principally
         invests in Mexican agricultural and horticultural businesses.
         Asesoria has sole investment authority with respect to the shares of
         Common Stock held by it.  Messrs. R. Vaquero, E. Vaquero, P. Vaquero,
         Camacho and Martinez share investment authority with the Scheduled
         Persons over the shares of Common Stock held by Asesoria.  Mr. R.
         Vaquero has sole investment authority with respect to the shares of
         Common Stock held by him.  Mr. E. Vaquero has sole investment
         authority with respect to the shares of Common Stock held by him.  Mr.
         P. Vaquero has sole investment authority with respect to the shares of
         Common Stock held by him.  Mr. Camacho has sole investment authority
         with respect to the shares of Common Stock held by him.  Mr. Martinez
         has sole investment authority with respect to the shares of Common
         Stock held by him.

         (d-f) During the last five (5) years, neither Asesoria nor Messrs. R.
         Vaquero, E. Vaquero, P. Vaquero, Camacho and Martinez nor any
         Scheduled Person has been convicted in any criminal proceeding
         (excluding traffic violation or similar misdemeanors) nor a party to a
         civil proceeding or a judicial or administrative body of competent
         jurisdiction and as a result of such proceeding was or is subject to a
         judgment, decree or final order enjoining future violations of, or
         prohibiting or mandating activities subject to, federal or state
         securities laws or finding any violation with respect to such laws.

         Each of the Scheduled Persons are citizens of Mexico.



<PAGE>   9
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                    PAGE 9 OF 12
                          Filed Pursuant to Rule 13D-1


ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

         The aggregate of 500,000 shares of Common Stock beneficially owned by
         Asesoria and Messrs. R. Vaquero, E.  Vaquero, P. Vaquero, Camacho and
         Martinez were purchased in a private transaction at an aggregate
         purchase price of $2,000,000 all of which was derived from working
         capital (in the case of Asesoria) and personal funds (in the case of
         Messrs. R. Vaquero, E. Vaquero, P. Vaquero, Camacho and Martinez).


ITEM 4.  PURPOSE OF TRANSACTION

         Asesoria and Messrs. R. Vaquero, E. Vaquero, P. Vaquero, Camacho and
         Martinez have acquired the shares of Common Stock in a privately
         negotiated transaction from Jorn Budde, the Company's President, Chief
         Executive Officer and Chairman.  In connection with this transaction,
         Mr. Budde has resigned all of his positions with the Company.  Rafael
         Vaquero, the Company's Chief Operating Officer, has been named
         President and Chief Executive Officer of the Company and Jakes
         Jordaan, a director of the Company, has been named Chairman of the
         Board.  In addition, the Company intends to add a Chief Financial
         Officer, with cross-border experience to its management team.  With
         the help of Dain Rauscher, the Company's financial advisors, Messrs.
         R. Vaquero, E.  Vaquero, P. Vaquero, Camacho and Martinez, as members
         of the Company's Board of Directors, are actively exploring all
         strategic alternatives to maximize shareholder value.

         Depending upon their evaluation of the Company, other investment
         opportunities, market conditions and such other factors as each may
         deem material, Asesoria and/or Messrs. R. Vaquero, E. Vaquero, P.
         Vaquero, Camacho and Martinez may seek to acquire additional shares of
         Common Stock in the open market, in private transactions, or
         otherwise, or may dispose of all or a portion of the shares of Common
         Stock.

         Except as set forth above, neither Asesoria nor Messrs. R. Vaquero, E.
         Vaquero, P. Vaquero, Camacho and Martinez has any plans or proposals
         of the type referred to in clauses (a) through (j) of Item 4 to
         Schedule 13D.


ITEM 5.  INTEREST IN SECURITIES OF THE ISSUER

         (a)     As of February 23, 1998, (i) Asesoria and each of the
                 Scheduled Persons beneficially owned 500,000 shares of Common
                 Stock representing approximately 5.8% of the outstanding
                 Common Stock of the Company, (ii) Mr. R. Vaquero beneficially
                 owned 726,236 shares of Common Stock (including the 500,000
                 shares of Common Stock beneficially owned by Asesoria),
                 representing approximately 8.4% of the outstanding Common
                 Stock of the Company, (iii) Mr. E. Vaquero beneficially owned
                 542,981




<PAGE>   10
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4
                                                                   PAGE 10 OF 12
                          Filed Pursuant to Rule 13D-1

                 shares of Common Stock (including the 500,000 shares of Common
                 Stock beneficially owned by Asesoria), representing
                 approximately 6.3% of the outstanding Common Stock of the
                 Company, (iv) Mr. P. Vaquero beneficially owned 563,000 shares
                 of Common Stock (including the 500,000 shares of Common Stock
                 beneficially owned by Asesoria), representing approximately
                 6.5% of the outstanding Common Stock of the Company, (v) Mr.
                 Camacho beneficially owned 706,565 shares of Common Stock
                 (including the 500,000 shares of Common Stock beneficially
                 owned by Asesoria), representing approximately 8.2% of the
                 outstanding Common Stock of the Company and (vi) Mr. Martinez
                 beneficially owned 546,800 shares of Common Stock (including
                 the 500,000 shares of Common Stock beneficially owned by
                 Asesoria), representing approximately 6.36% of the outstanding
                 Common Stock of the Company.

         (b)     Mr. R. Vaquero has the sole power to vote and dispose of the
                 Common Stock beneficially owned by him.  Mr. E. Vaquero has
                 the sole power to vote and dispose of the Common Stock
                 beneficially owned by him.  Mr. P. Vaquero has the sole power
                 to vote and dispose of the Common Stock beneficially owned by
                 him.  Mr. Camacho has the sole power to vote and dispose of
                 the Common Stock beneficially owned by him.  Mr.  Martinez has
                 the sole power to vote and dispose of the Common Stock
                 beneficially owned by him.

                 Messrs. R. Vaquero, E. Vaquero, P. Vaquero, Camacho and
                 Martinez and each of the Scheduled Persons share the power to
                 vote and dispose of the shares of Common Stock owned by
                 Asesoria through their management of Asesoria.

         (c)     Not applicable.

         (d)     Not applicable.

         (e)     Not applicable.


ITEM 6.  CONTRACTS, ARRANGEMENTS, OR UNDERSTANDINGS WITH RESPECT TO SECURITIES
         OF THE ISSUER

                 Not applicable.


ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS

                 Exhibit 7A --    Stock Purchase Agreement between Jorn Budde
                                  and Asesoria Garza Jasso, S.C. (1)



<PAGE>   11
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4                                           PAGE 11 OF 12
                          Filed Pursuant to Rule 13D-1

                 Exhibit 7B --    Promissory Note between Asesoria Garza Jasso,
                                  S.C. and Jorn Budde (1)

                 Exhibit 7C --    Pledge Agreement between Asesoria Garza
                                  Jasso, S.C. and Jorn Budde (1)

                 Exhibit 7D --    General Partnership Agreement accompanied by
                                  a summary in the English language (2)
                 ________________________________________ 
                 (1)  Filed herewith
                 (2)  To be filed by amendment


                                   SIGNATURE

         After reasonable inquiry, I certify that to the best of my knowledge
and belief the information set forth in this statement is true, complete and
correct.

Dated:  February 27, 1998
                                        ASESORIA GARZA JASSO, S.C.


                                        By:    /s/  Rafael Vaquero Bazan 
                                              -----------------------------
                                        Name:  Rafael Vaquero Bazan 
                                              -----------------------------
                                        Title: General Partner
                                              -----------------------------
<PAGE>   12
                                  SCHEDULE 13D
CUSIP NO.  904789 10 4                                            PAGE 12 OF 12
                          Filed Pursuant to Rule 13D-1

                                    ANNEX I

                        DIRECTORS AND EXECUTIVE OFFICERS
                                       OF
                           ASESORIA GARZA JASSO, S.C.

Set forth below is the name, business address and present principal occupation
or employment of each director and executive officer of Asesoria Jasso Garza
S.C. ("Asesoria").  Each individual listed below is a citizen of Mexico, and
unless otherwise noted devotes full time to the business of Asesoria.

<TABLE>
<S>                                   <C>                                    <C>
                                      Present Principal
                                      Occupation or                          Business
Name                                  Employment                             Address  
- ----                                  -----------------                      ---------

Rafael Vaquero Bazan                  President and Chief                    Huerta Mexiquito S/N
                                         Executive Officer of                Montemorelos, N.L.
                                         The UniMark Group, Inc.             Mexico

Eduardo Vaquero Bazan                 Director of Finance                    Calderon Esquina con
                                         of Industrias Citricolas de            Tampico #100
                                         Montemorelos, S.A. de               Montemorelos, N.L.
                                         C.V. and Director of                Mexico C.P. 67530
                                         UniMark Group, Inc.

Jose Ma. Martinez Brohez              President of Grupo                     Cristobal Colon No. 2007 Nte.
                                         Industrial Santa                    Francc. San Jose
                                         Engracia and Director of            Cd. Victoria, Tamps.
                                         The UniMark Group, Inc.             Mexico

Fernando Camacho Casas                General Director of                    Rio Neva 17
                                         Operadora Agros,                    Col. Cuauthemoc
                                         S.A. de C.V.                        Del. Cuauthemoc
                                                                             C.P. 06500
                                                                             Mexico D.F.
</TABLE>
<PAGE>   13
                                 EXHIBIT INDEX


<TABLE>
<CAPTION>
EXHIBIT
NUMBER                        DESCRIPTION
- -------                       -----------
<S>          <C>
Exhibit 7A -- Stock Purchase Agreement between Jorn Budde and Asesoria Garza
              Jasso, S.C. (1)

Exhibit 7B -- Promissory Note between Asesoria Garza Jasso, S.C. and Jorn Budde
              (1)

Exhibit 7C -- Pledge Agreement between Asesoria Garza Jasso, S.C. and Jorn Budde
              (1)

Exhibit 7D -- General Partnership Agreement accompanied by a summary in the
              English language (2)
</TABLE>

- ------------------
(1) Filed herewith
(2) To be filed by amendment




<PAGE>   1
                                                                    EXHIBIT 7A



                            STOCK PURCHASE AGREEMENT

         This Stock Purchase Agreement (this "Agreement") is made and entered
into as of the 18th day of February, 1998 by and between Jorn Budde (the
"Seller") and Asesoria Garza Jasso, S.C., a Mexican entity ("Buyer").

                               W I T N E S S E T H

         1. Seller is the owner of at least 500,000 shares of the issued and
outstanding shares of common stock, $.01 par value per share (the "SHARES") of
The UniMark Group, Inc., a Texas corporation (the "CORPORATION").

         2. This Agreement provides for the transfer, conveyance and assignment
by the Sellers to the Buyer, in exchange for the consideration hereinafter set
forth, of the Shares.

         NOW, THEREFORE, in consideration of the mutual covenants herein
contained, the parties hereto agree as follows:

1.   SALE AND PURCHASE OF STOCK

     Subject to the terms and conditions herein stated, the Seller agrees to
sell, assign, transfer and deliver to the Buyer on the Closing Date, and the
Buyer agrees to purchase from Seller on the Closing Date, the Shares. For the
purchase price hereinafter set forth, and on the terms and subject to the
conditions set forth in this Agreement, Seller will, at the Closing (as
hereinafter defined), sell, assign, convey, transfer and deliver to Buyer, free
and clear of all liens and encumbrances of every kind and description and Buyer
will purchase from Seller, the Shares.

2.   PURCHASE PRICE OF STOCK

     In consideration of the sale by Seller of the Shares, and in full and
complete payment therefor, Buyers agrees, subject to the terms and conditions
contained herein, to pay Seller as follows:

                  (a)    $2,000,000.00 in cash; and

                  (b)    $500,000.00 by Buyers' execution and delivery to 
                  Seller of a promissory note in substantially the form of
                  Exhibit "A" attached hereto (the "Note"). The Note will (a)
                  bear interest at nine percent (9%) per annum compounded
                  annually and (b) be secured by the Shares pursuant to the
                  terms of a Pledge Agreement, in substantially the form of
                  Exhibit "B" attached hereto (the "Pledge Agreement"). In
                  addition each of the of the partners of Buyer will personally
                  guarantee payment of the Note.



<PAGE>   2

3.   ESCROW

     Simultaneous with the execution of this Agreement:

                  (a) Buyer shall wire transfer $2,000,000.00 to the Trust
                  Account of Jordaan & Pennington, PLLC at NationsBank, NA, and
                  deliver executed originals of the Note and Pledge Agreement to
                  Jordaan & Pennington, PLLC; and

                  (b) Seller shall deliver to Jordaan & Pennington, PLLC the
                  certificates representing the Shares, duly endorsed in blank
                  by the Seller. Seller agrees to cure any deficiencies with
                  respect to the endorsement of the certificates representing
                  the Shares owned by Seller or with respect to the stock power
                  and rights accompanying any such certificates.

4.   CLOSING

     The sale referred to in Section 1.1 shall take place at 9 a.m. at the
offices of Jordaan & Pennington, PLLC on February 18, 1998, or at such other
time and date as the parties hereto shall by written instrument designate. At
the Closing, Jordaan & Pennington, PLLC will:

                  (A)  release $2,000,000 in cash to Seller;

                  (B) deliver the Note to Seller;

                  (C) Deliver and the Pledge Agreement to the Seller; and

                  (D) Release the Shares to Buyer.

At the Closing, the parties hereto will execute and deliver such documents as
may be necessary to vest complete and indefeasible title to the Shares in Buyer.
Buyer and Seller shall execute and deliver such other documents and instruments
and take such further action as may be necessary or appropriate to consummate
the transactions contemplated by this Agreement.

5.   REPRESENTATIONS, WARRANTIES AND COVENANTS OF SELLER

     Seller hereby represents, warrants and covenants with Buyer as follows:

     Section 5.1 Ownership of Shares. Seller is the lawful owner of the Shares,
free and clear of all hypothecs, liens, encumbrances restrictions and claims of
every kind except restrictions imposed by federal and state securities laws;
Seller has full legal right, power and authority to enter into this Agreement
and to sell, assign, transfer and convey the Shares pursuant to this Agreement;
and the delivery to the Buyer of the Shares pursuant to the provisions of this
Agreement will transfer to the



                                       2
<PAGE>   3

Buyer valid title thereto, free and clear of all hypothecs, liens, encumbrances,
restrictions and claims of every kind, except restrictions imposed by federal
and state securities laws.

     Section 5.2 Validity of Transaction. This Agreement is a valid and legally
binding obligation, enforceable in accordance with its terms, except as limited
by bankruptcy, insolvency and similar laws affecting creditors generally. When
sold, assigned, transferred and conveyed to the Buyer pursuant to this
Agreement, the Shares will be duly authorized, validly issued, fully paid,
nonassessable.


6.   REPRESENTATIONS AND WARRANTIES OF BUYER

     Buyer hereby represents and warrants to Seller as follows:

     Section 6.1 Purchase for Investment. Buyer will acquire the Shares for its
own account for investment and not with a view toward any resale or distribution
thereof.

     Section 6.2 Validity of Transaction. This Agreement is a valid and legally
binding obligation, enforceable in accordance with its terms, except as limited
by bankruptcy, insolvency and similar laws affecting creditors generally.


7.   EXPENSES

     Each party shall bear its own costs and expenses, including fees and
expenses of counsel, incurred in connection with the transactions contemplated
by this Agreement.

8.   GOVERNING LAW

     This Agreement shall be construed and enforced in accordance with the laws
of the State of Texas.

9.   PUBLIC ANNOUNCEMENTS

     Neither party will make any public announcement or otherwise disclose the
existence or terms of this Agreement without the prior written consent of the
other party.

10.  SEVERABILITY

     The provisions of this Agreement shall be deemed independent and severable
and the invalidity or partial invalidity or unenforceability of any one
provision shall not affect the validity or enforceability of any other
provision.

11.  ADDITIONAL INSTRUMENTS



                                       3
<PAGE>   4

     Sellers and Buyer shall each execute, acknowledge and deliver to the other
any further instruments or documents that may be reasonably required to give
full force and effect to the provisions of this Agreement and in order to vest
title to the Shares in Buyer.

12.  COUNTERPARTS

     This Agreement may be executed in any number of counterparts, each of which
when executed and delivered shall be an original, but all counterparts shall
constitute one and the same instrument.

     IN WITNESS WHEREOF, the parties have caused this Agreement to be executed
by their respective authorized officers, as of the date first above written.

                                     SELLER:


                                     /s/ Jorn Budde
                                     ------------------------------------
                                     Jorn Budde


                                     BUYER:

                                     Asesoria Garza Jasso, S.C.


                                     By: /s/ Rafael Vaquero Bazan
                                         ---------------------------------
                                         Rafael Vaquero Bazan, an
                                         Authorized Officer




                                       4
<PAGE>   5






                                    EXHIBIT A






                             Form of Promissory Note




<PAGE>   6


                                 PROMISSORY NOTE

$500,000.00                       Dallas, Texas                February 18, 1998


     FOR VALUE RECEIVED, the undersigned, Asesoria Garza Jasso, S.C., a Mexican
entity ("Maker"), promises to pay to the order of Jorn Budde ("Payee"), the
principal sum of Five Hundered Thousand Dollars ($500,000.00), payable as
provided herein, plus accrued interest on the outstanding principal balance, at
a rate of nine percent (9%) per annum as herein specified.

     The principal plus accrued interest thereon shall be due and payable by the
Maker to the Payee on the earlier of (a) February 18, 1999 or (b) any sale of
the Shares. Principal and accrued interest under this Note, or any portion
thereof, may be prepaid without penalty. All payments and prepayments shall be
applied first to accrued and unpaid interest, and the balance of any such
payments or prepayments shall be applied to outstanding principal in the order
of maturity.

     Not withstanding anything to the contrary contained herein, no provisions
of this Note shall require the payment or permit the collection of interest in
excess of the maximum rate permitted by applicable law. If any interest in
excess of such maximum rate is herein provided for, or shall be adjudicated to
be so provided, in this Note or otherwise in connection with this transaction
giving rise to the execution hereof, the provisions of this paragraph shall
govern and prevail, and neither Maker nor the sureties, guarantors, successors
or assigns of the Maker shall be obligated to pay the excess amount of such
interest or any other excess sum paid for the use, forbearance or detention of
sums loaned pursuant hereto. If for any reason interest in excess of the maximum
rate of interest permitted by applicable law shall be deemed, charged, required
or permitted by a court of competent jurisdiction, any such excess shall be
applied as a payment and reduction of the principal of indebtedness evidenced by
this Note; and, if the principal amount hereof has been paid in full, any
remaining excess shall forthwith be paid to Maker.

     This Note is secured by a pledge agreement dated February 18, 1998,
executed by the undersigned in favor of the holder hereto, covering 200,000
shares of Common Stock of The UniMark Group, Inc. (the "Collateral").

     This Note is issued and delivered under and is subject to the terms and
provisions of that certain initial Stock Purchase Agreement (the "Purchase
Agreement") dated February 18, 1998, by and among maker and Payee.

     Maker, and any endorser or guarantors of this Note and all other persons
who may become liable for all or any part of the obligations represented by this
Note, severally waive presentment for payment, protest, notice of protest and of
nonpayment, notice of intention to accelerate, and notice of acceleration.

     In the event of default by Maker in the payment of any part of the
principal or interest on this Note when due and the continuance thereof for ten
(10) days following Maker's receipt of written notice of such default, the
entire unpaid balance of principal and accrued interest on this Note shall,




<PAGE>   7

at the option of the holder hereof, become immediately due and payable. Failure
by the holder to exercise any option upon one (1) default will not constitute a
waiver thereof or the waiver of the right to exercise such option in the event
of a subsequent default. If after default this Note is placed in the hands of an
attorney for collection or is collected through judicial proceedings, Maker
shall pay, in addition to the sums referred to above, a reasonable sum as
collection or attorneys' fees and all other costs incurred by the holder in
collection of the unpaid amounts due hereunder.

     This note is made and is performable in Argyle, Denton County, Texas, and
Maker waives the right to be sued hereon elsewhere. This Note shall be governed
by and construed in accordance with the laws of the State of Texas and the
applicable laws of the United States of America.

     IN WITNESS WHEREOF, the undersigned has executed this Note as of the 18th
day of February, 1998.


                                      MAKER:

                                      Asesoria Garza Jasso, S.C.
                                      A Mexican entity


                                      By:   /s/ Rafael Vaquero Bazan
                                            ------------------------------
                                            Name: Rafael Vaquero Bazan
                                                  An Authorized Officer



<PAGE>   8


Payment of the preceding promissory note is personally guaranteed by the
undersigned.


<TABLE>
<S>                                      <C>
 /s/ Rafael Vaquero Bazan                /s/ Lorenzo Zambrano Trevino
- ---------------------------------        ---------------------------------
Rafael Vaquero Bazan                     Lorenzo Zambrano Trevino

 /s/ Eduardo Vaquero Bazan               /s/ Rafael J. Fco. Hernandez
- ---------------------------------        ---------------------------------
Eduardo Vaquero Bazan                    Rafael J. Fco. Hernandez

 /s/ Carlos Vaquero Bazan                /s/ Jorge Gutierrez Welsh
- ---------------------------------        ---------------------------------
Carlos Vaquero Bazan                     Jorge Gutierrez Welsh

 /s/ Pedro Vaquero Bazan                 /s/ Pedro Garza Salazar
- ---------------------------------        ---------------------------------
Pedro Vaquero Bazan                      Pedro Garza Salazar

 /s/ Pedro Vaquero Garcia                /s/ Pedro Villareal Lozano
- ---------------------------------        ---------------------------------
Pedro Vaquero Garcia                     Pedro Villareal Lozano

 /s/ Jose Ma. Martinez Brohez    
- ---------------------------------
Jose Ma. Martinez Brohez

 /s/ Frederico Martinez Brohez   
- ---------------------------------
Frederico Martinez Brohez

 /s/ Jorge Martinez Brohez       
- ---------------------------------
Jorge Martinez Brohez

 /s/ Fernando Camacho Casas     
- ---------------------------------
Fernando Camacho Casas

 /s/ Enrique Portilla
- ---------------------------------
Enrique Portilla

 /s/ Francisco Domenech Tarrago
- ---------------------------------
Francisco Domenech Tarrago

 /s/ Dr. David Madero Gonzalez  
- ---------------------------------
Dr. David Madero Gonzalez

 /s/ Pedro Pierter Villarreal
- ---------------------------------
Pedro Pierter Villarreal
</TABLE>




<PAGE>   9








                                    EXHIBIT B









                            Form of Pledge Agreement



<PAGE>   10
                                PLEDGE AGREEMENT

         THIS PLEDGE AGREEMENT (this "Agreement"), dated as of February 18,
1998, between Asesoria Garza Jasso, S.C, a Mexican partnership (the "Pledgor"),
and Jorn Budde (the "Secured Party").

                              W I T N E S S E T H:

         WHEREAS, the Pledgor has entered into that certain Stock Purchase
Agreement dated as of February 18, 1998 (the "Purchase Agreement" certain
capitalized terms used herein which are defined in the Purchase Agreement shall
have the same meanings when used herein, unless otherwise defined herein) with
the Secured Party, pursuant to which, among other things, the Pledgor has agreed
to purchase and the Secured Party has agreed to sell to the Pledgor the Shares
and Pledgor has agreed to execute and deliver the Note; and

         WHEREAS, under the terms of the Purchase Agreement, that the Pledgor
has agreed to execute and deliver this Security Agreement and grant the security
interests contemplated hereby; and

         WHEREAS, this Agreement, the Purchase Agreement, and the Note are
hereinafter sometimes referred to as the "Loan Documents".

         NOW, THEREFORE, for good and valuable consideration the receipt of
which is hereby acknowledged by it, and in order to induce the Secured party to
sell the Shares, Pledgor agrees with the Secured Party, as follows:

                                    ARTICLE 1

                                   DEFINITIONS

          SECTION 1.1    Certain Terms. The following terms (whether or not
underscored) when used in this Agreement, including its preamble and recitals,
shall have the following meanings (such definitions to be equally applicable to
the singular and plural forms thereof):

         "Collateral" is defined in Section 2.1.

         "Distributions" means all stock dividends, liquidating dividends,
shares of stock resulting from stock splits, reclassifications, warrants,
options, non-cash dividends and other distributions (whether similar or
dissimilar to the foregoing) on or with respect to any Pledged Shares or other
shares of capital stock constituting Collateral, but shall not mean Dividends.

         "Dividends" means cash dividends and cash distributions with respect to
any Pledged Shares made out of capital surplus.

         "Initial Pledged Shares" means the 200,000 shares of Common Stock of
UniMark. 


                                      -1-
<PAGE>   11

         "Pledged Property" means all Pledged Shares, and all other pledged
shares of capital stock, all other securities, all assignments of any amounts
due or to become due, all other instruments which are now being delivered by the
Pledgor to the Secured Party or may from time to time hereafter be delivered by
the Pledge or to the Secured Party for the purpose of pledge under this 
Agreement or any other Loan Document, and all proceeds of any of the foregoing.

         "Pledged Shares" means the Initial Pledged Shares and all other shares
of capital stock of UniMark, if any, which are delivered by the Secured Party as
Pledged Property hereunder.

         "Pledgor" is defined in the preamble.

         "Purchase Agreement" is defined in the first recital.

         "Secured Obligations" is defined in Section 2.2.

         "U.C.C." means the Uniform Commercial Code as in effect in the State of
Texas.

         "UniMark" means The UniMark group, Inc., a Texas corporation.


         SECTION 1.2     Purchase Agreement Definitions. Etc. Unless otherwise
defined herein or the context otherwise requires, terms used in this Agreement,
including its preamble and recitals, have the meanings provided in the Purchase
Agreement. References to the masculine gender shall include the feminine and
neuter genders unless the context otherwise requires.

         SECTION 1.3     U.C.C. Definitions. Unless otherwise defined herein or 
the context otherwise requires, terms for which meanings are provided in the
U.C.C. are used in this Agreement, including its preamble and recitals, with
such meanings.


                                   ARTICLE 2

                                     PLEDGE

         SECTION 2.1     Grant of Security Interest. Pledgor hereby pledges,
assigns, charges, mortgages, delivers and transfers to the Secured Party, and
hereby grants to the Secured Party, a continuing security interest in, all of
the following property (the "Collateral"):

         (a)   the Initial Pledged Shares;

         (b)   all Pledged Shares issued from time to time;

         (c)   all other Pledged Property, whether now or hereafter delivered 
         to the Secured Party in connection with this Agreement;



                                      -2-
<PAGE>   12
         (d)   all Dividends, Distributions, interest and other payments and
         rights with respect to any Pledged Property; and

         (e)   all proceeds of any of the foregoing.

         SECTION 2.2     Security for Secured Obligations. This Agreement 
secures the payment in full of the Note, whether for principal, interest, costs,
fees, expenses or otherwise, and all obligations now or hereafter existing
(collectively, the "Secured Obligations").

         SECTION 2.3     Delivery of Pledged Property; Registration of Pledge,
Transfer, etc. All certificates and Instruments representing or evidencing any
Collateral, including all Pledged Shares, shall be delivered to and held by or
on behalf of the Secured Party pursuant hereto, shall be in suitable form for
transfer by delivery, and shall be accompanied by all necessary Instruments of
transfer or assignment, duly executed in blank.

         SECTION 2.4     Continuing Security Interest; Transfer of Note.  This 
Agreement shall

         (a)   create a continuing security interest in the Collateral;

         (b)   remain in full force and effect until payment in full of all
         Secured Obligations;

         (c)   be binding upon Pledgor, its successors and assigns; provided 
         that Pledgor may not assign any of its rights or obligations hereunder
         without the prior written consent of the Secured Party; and

         (d)   inure to the benefit of the Secured Party and his heirs and 
         legal representatives.


                                    ARTICLE 3

                         REPRESENTATIONS AND WARRANTIES

         SECTION 3.1     Warranties, etc. Pledgor represents and warrants unto 
the Secured Party that as at the date of each pledge hereunder (including each
pledge of Pledged Shares) by Pledgor to the Secured Party of any Collateral,

         (a)   Pledgor has all requisite power and authority, and has taken all
         necessary corporate action, to execute and deliver and perform its
         obligations under this Pledge Agreement and to pledge the Collateral
         hereunder.

         (b)   Pledgor will be the legal and beneficial owner of, and will have
         good and marketable title to (and will have full right and authority to
         pledge and assign) all Collateral, free and clear of all Liens or other
         charges or encumbrances, except any Lien or security interest granted
         pursuant hereto in favor of the Secured Party.


                                      -3-
<PAGE>   13
         (c)   The delivery of the Collateral (including the delivery of the
         Initial Pledged Shares) to the Secured Party will be effective to
         create a valid, perfected, first priority security interest in such
         Collateral and all proceeds thereof, securing the Secured Obligations,
         and no filing or other action will be necessary to perfect or protect
         such security interest.

         (d)   In the case of any Pledged Shares constituting Collateral, all of
         such Pledged Shares will be duly authorized and validly issued, fully
         paid, and non-assessable.

                                    ARTICLE 4

                                    COVENANTS

         SECTION 4.1     Protect Collateral; Further Assurances. etc. Pledgor 
will not sell, assign, transfer, pledge or encumber in any other manner the
Collateral (except in favor of the Secured Party hereunder). Pledgor will
warrant and will use its best efforts to defend the right and title herein
granted unto the Secured Party in and to the Collateral (and all right, title
and interest represented by the Collateral) against the claims and demands of
all Persons whomsoever. Pledgor agrees that at any time, and from time to time,
at the expense of Pledgor, Pledgor will promptly execute and deliver all further
Instruments, and take all further action, that may be necessary or desirable, or
that the Secured Party may reasonably request, in order to perfect and protect
any security interest granted or purported to be granted hereby or to enable the
Secured Party to exercise and enforce its rights and remedies hereunder with
respect to any Collateral.

         SECTION 4.2     Stock Powers, etc. Pledgor agrees that all Pledged 
Shares (and all other shares of capital stock constituting Collateral) delivered
by Pledgor pursuant to this Agreement will be accompanied by duly executed
undated blank stock powers, or other equivalent Instruments of transfer
acceptable to the Secured Party. Pledgor will, from time to time upon the
request of the Secured Party, promptly deliver to the Secured Party such stock
powers, Instruments and similar documents, satisfactory in form and substance to
the Secured Party, with respect to the Collateral as the Secured Party may
reasonably request and will, from time to time upon the request of the Secured
Party after the occurrence of any Default, promptly transfer any Pledged Shares
or other shares of Stock constituting Collateral into the name of the Secured
Party or any nominee designated by the Secured Party.

         SECTION 4.3     Continuous Pledge. Pledgor will, at all times, keep
pledged to the Secured Party pursuant hereto all Pledged Shares and all other
shares of Stock constituting Collateral, all Dividends and Distributions with
respect thereto, and all other Collateral and other securities, instruments,
proceeds and rights from time to time received by or distributable to Pledgor in
respect of any Collateral.

         SECTION 4.4     Voting Rights; Dividends, etc. Pledgor agrees to 
deliver all Distributions at any time received by it to the Secured Party to be
held as Collateral hereunder and, in addition, to deliver (properly endorsed
where required hereby or requested by the Secured Party) to the Secured Party:



                                      -4-
<PAGE>   14
         (a)   after any Default shall have occurred and be continuing or if any
         Default shall occur as a result thereof, promptly upon receipt thereof
         by Pledgor and without any request therefor by the Secured Party, all
         Dividends, all other cash payments and all proceeds of the Collateral,
         all of which shall be held by the Secured Party as additional
         collateral; and

         (b)   after any Default shall have occurred and be continuing, promptly
         upon request of the Secured Party, such proxies and other documents as
         may be necessary to allow the Secured Party to exercise the voting
         power with respect to any share of capital stock constituting
         Collateral;

provided, however, that unless a Default shall have occurred and be continuing
or result therefrom, Pledgor shall be entitled to exercise, in its reasonable
judgment, but in a manner not inconsistent with the terms of the Purchase
Agreement or any other Loan Document (including this Agreement), the voting
power and all other incidental rights of ownership with respect to any Pledged
Shares or other shares of capital stock constituting Collateral (subject to
Pledgor's obligation to deliver to the Secured Party such Pledged Shares and
other shares in pledge hereunder).

All Dividends, Distributions, cash payments and proceeds which may at any time
and from time to time be held by Pledgor but which Pledgor is then obligated to
deliver to the Secured Party, shall, until delivery to the Secured Party, be
held by Pledgor separate and apart from its other property in trust for the
Secured Party. The Secured Party agrees that unless a Default shall have
occurred and be continuing, the Secured Party shall, upon the written request of
Pledgor, promptly deliver such proxies and other documents, if any, as shall be
reasonably requested by Pledgor which are necessary to allow Pledgor to exercise
voting power with respect to any share of capital stock (including Pledged
Shares) constituting Collateral; provided, however that no vote shall be cast,
or consent, waiver or ratification given, or action taken by Pledgor that would
impair any Collateral or be inconsistent with or violate any provision of the
Purchase Agreement or any other Loan Document (including this Agreement).


                                    ARTICLE 5

                                    REMEDIES

         SECTION 5.1     Actions upon Event of Default. In addition to its 
rights and remedies provided hereunder, whenever an Event of Default shall
occurred and be continuing, the Secured Party shall have all rights and remedies
of a secured party upon default under the U.C.C. or other applicable law. Any
notification required by law of any intended disposition by the Secured Party of
any of the Collateral shall be deemed reasonably and properly given if given at
least 15 days before such disposition. Without limitation of the above, the
secured Party may, whenever an Event of Default shall have occurred and be
continuing, without prior notice to Pledgor, take all or any of the following
actions: 

         (a)   transfer all or any part of the Collateral into the name of the
         Secured Party or its nominee, with or without disclosing that such
         Collateral is subject to the Lien and security interest hereunder;



                                      -5-
<PAGE>   15

         (b)   notify the parties obligated on any of the Collateral to make 
         payment to the Secured Party of any amount due or to become due 
         thereunder;

         (c)   enforce collection of any of the Collateral by suit or otherwise,
         and surrender, release or exchange all or any part thereof, or
         compromise or extend or renew for any period (whether or not longer
         than the original period) any obligations of any nature of any party
         with respect thereto;

         (d)   endorse any checks, drafts, or other writings in Pledgor's name
         to allow collection of the Collateral;

         (e)   take control of any proceeds of the Collateral; and

         (f)   execute (in the name, place and stead of Pledgor) endorsements,
         assignments, stock powers and other instruments of conveyance or
         transfer with respect to all or any of the Collateral.

         SECTION 5.2     Attorney-in-Fact. Pledgor hereby irrevocably appoints 
the Secured Party its attorney-in-fact, with full authority in the place and
stead of Pledgor and in the name of Pledgor, the Secured Party, or otherwise,
from time to time in the Secured Party's discretion, to take any action and to
execute any Instrument which the Secured Party may deem necessary or advisable
to accomplish the purposes of this Agreement, including, upon the occurrence and
continuance of an Event of Default, all actions described in Section 5.1.

         SECTION 5.3     Private Sales.

         (a)   Pledgor recognizes that the Secured Party may be unable to effect
         a public sale of any or all the Pledged Shares by reason of certain
         prohibitions contained in the Securities Act of 1933, as amended (the
         "Securities Act") and applicable state securities laws or otherwise,
         and may be compelled to resort to one or more private sales thereof to
         a restricted group of purchasers that will be obliged to agree, among
         other things, to acquire such securities for their own account for
         investment and not with a view to the distribution or resale thereof.
         Pledgor acknowledges and agrees that any such private sale may result
         in prices and other terms less favorable than if such sale were a
         public sale and, notwithstanding such circumstances, agrees that any
         such private sale shall be deemed to have been made in a commercially
         reasonable manner. The Secured Party shall be under no obligation to
         delay sale of any of the Pledged Shares for the period of time
         necessary to permit the Pledgor to register such securities for public
         sale under the Securities Act, or under applicable state securities
         laws, even if UniMark would agree to do so.

         (b)   Pledgor further agrees to use its best efforts to do or cause 
         to be done all such acts as may be necessary to make such sale or
         sales of all or any portion of the Pledged Shares pursuant to this
         Section 5.3 valid and binding and in compliance with any and all other
         applicable Requirements of Law.


                                    ARTICLE 6



                                      -6-
<PAGE>   16

                                  MISCELLANEOUS

         SECTION 6.1     Loan Document. This Agreement is a Loan Document 
executed pursuant to the Purchase Agreement and shall (unless otherwise
expressly indicated herein) be construed, administered and applied in accordance
with the terms and provisions thereof.

         SECTION 6.2     Amendments, etc. No amendment or waiver of any 
provision of this Agreement nor consent to any departure by Pledgor herefrom
shall in any event be effective unless the same shall be in writing, signed by
the Secured Party and then such waiver or consent shall be effective only in the
specific instance and for the specific purpose for which it is given.

         SECTION 6.3     Obligations Not Affected. The obligations of Pledgor
under this Agreement shall remain in full force and effect without regard to,
and shall not be impaired or affected by:

         (a)   any amendment or modification or addition or supplement to the
         Purchase Agreement, any Note, any other Loan Document, any Instrument
         delivered in connection therewith or any assignment or transfer
         thereof;

         (b)   any exercise, non-exercise or waiver by the Secured Party of any
         right, remedy, power or privilege under or in respect of, or any
         release of any guaranty or collateral provided pursuant to, this
         Agreement, the Purchase Agreement, or any Loan Document;

         (c)   any waiver, consent, extension, indulgence or other action or
         inaction in respect of this Agreement, the Purchase Agreement or any
         Loan Document or any assignment or transfer of any thereof; or

         (d)   any bankruptcy, insolvency, reorganization, arrangement,
         readjustment, composition, liquidation or the like, death or
         incompetency of the Pledgor or any other Person, whether or not Pledgor
         shall have notice or knowledge of any of the foregoing.

         SECTION 6.4     Protection of Collateral. The Secured Party may from 
time to time, at its option, perform any act which Pledgor agrees hereunder to
perform and which Pledgor shall fail to perform after being requested in writing
to so perform (it being understood that no such request need be given after the
occurrence and during the continuance of a Default) and the Secured Party may
from time to time take any other action which the Secured Party reasonably deems
necessary for the maintenance, preservation or protection of any of the
Collateral or of its security interest therein.



                                      -7-
<PAGE>   17

         SECTION 6.5     Governing Law; Jurisdiction.

         (a)   THIS AGREEMENT SHALL BE DEEMED TO BE A CONTRACT MADE UNDER AND
GOVERNED BY THE INTERNAL LAWS OF THE STATE OF TEXAS.

         (b)   EACH PARTY TO THIS AGREEMENT HEREBY IRREVOCABLY SUBMITS TO THE
JURISDICTION OF ANY TEXAS STATE OR FEDERAL COURT SITTING IN DALLAS, TEXAS IN ANY
ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT OR ANY OTHER
LOAN DOCUMENT OR RELATED DOCUMENT (AND PLEDGOR AGREES THAT SUCH JURISDICTION
WILL BE EXCLUSIVE WITH RESPECT TO CLAIMS BROUGHT BY PLEDGOR AGAINST THE SECURED
PARTY), AND EACH HEREBY IRREVOCABLY AGREES THAT ALL CLAIMS IN RESPECT OF SUCH
ACTION OR PROCEEDING MAY BE HEARD AND DETERMINED IN SUCH TEXAS STATE OR FEDERAL
COURT. EACH PARTY TO THIS AGREEMENT HEREBY IRREVOCABLY WAIVES, TO THE FULLEST
EXTENT IT MAY EFFECTIVELY DO SO, THE DEFENSE OF ANY INCONVENIENT FORUM TO THE
MAINTENANCE OF SUCH ACTION OR PROCEEDING.

         (c)   Pledgor hereby irrevocably designates, appoints and empowers
Rafael Vaquero Bazan, as its authorized agent to receive, for and on its behalf
and on behalf of its property, service of process in the State of Texas when and
as such legal actions or proceedings may be brought in the courts of the State
of Texas or of the United States of America sitting in Texas, and such service
of process shall be deemed complete upon the date of delivery thereof to such
agent whether or not such agent gives notice thereof to Pledgor, or upon the
earliest of any other date permitted by applicable law. It is understood that a
copy of said process served on such agent will as soon as practicable be
forwarded to Pledgor, at its address set forth below, but Pledgor's failure to
receive such copy shall not affect in any way the service of said process on
said agent as the agent of Pledgor. Pledgor irrevocably consents to the service
of process out of any of the aforementioned courts in any such action or
proceeding by the mailing of the copies thereof by certified mail, return
receipt requested, postage prepaid, to Pledgor at its address set forth below,
such service to become effective upon the earlier of (i) the date 10 calendar
days after such mailing or (ii) any earlier date permitted by applicable law.
Pledgor agrees that it will at all times continuously maintain an agent to
receive service of process in the State of Texas and in the event that, for any
reason, the agent named above or its successor shall no longer serve as its
agent to receive service of process in the State of Texas on its behalf, it
shall promptly appoint a successor so to serve and shall advise the Secured
Party.



                                      -8-
<PAGE>   18


         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as of the day and year first above written.


                                     ASESORIA GARZA JASSO, S.C


                               By:   /s/ Rafael Vaquero Bazan
                                     --------------------------------------
                                     Rafael Vaquero Bazan, An Authorized Officer




                                     /s/ Jorn Budde
                                     --------------------------------------
                                     Jorn Budde



                                      -9-

<PAGE>   1
                                                                      EXHIBIT 7B


                                PROMISSORY NOTE

$500,000.00                                           Dallas, Texas
February 18, 1998


         FOR VALUE RECEIVED, the undersigned, Asesoria Garza Jasso, S.C., a
Mexican entity ("Maker"), promises to pay to the order of Jorn Budde
("Payee"), the principal sum of Five Hundered Thousand Dollars ($500,000.00),
payable as provided herein, plus accrued interest on the outstanding principal
balance, at a rate of nine percent (9%) per annum as herein specified.

         The principal plus accrued interest thereon shall be due and payable
by the Maker to the Payee on the earlier of (a) February 18, 1999 or (b) any
sale of the Shares.  Principal and accrued interest under this Note, or any
portion thereof, may be prepaid without penalty.  All payments and prepayments
shall be applied first to accrued and unpaid interest, and the balance of any
such payments or prepayments shall be applied to outstanding principal in the
order of maturity.

         Not withstanding anything to the contrary contained herein, no
provisions of this Note shall require the payment or permit the collection of
interest in excess of the maximum rate permitted by applicable law.  If any
interest in excess of such maximum rate is herein provided for, or shall be
adjudicated to be so provided, in this Note or otherwise in connection with
this transaction giving rise to the execution hereof, the provisions of this
paragraph shall govern and prevail, and neither Maker nor the sureties,
guarantors, successors or assigns of the Maker shall be obligated to pay the
excess amount of such interest or any other excess sum paid for the use,
forbearance or detention of sums loaned pursuant hereto.  If for any reason
interest in excess of the maximum rate of interest permitted by applicable law
shall be deemed, charged, required or permitted by a court of competent
jurisdiction, any such excess shall be applied as a payment and reduction of
the principal of indebtedness evidenced by this Note; and, if the principal
amount hereof has been paid in full, any remaining excess shall forthwith be
paid to Maker.

         This Note is secured by a pledge agreement dated February 18, 1998,
executed by the undersigned in favor of the holder hereto, covering 200,000
shares of Common Stock of The UniMark Group, Inc. (the "Collateral").

         This Note is issued and delivered under and is subject to the terms
and provisions of that certain initial Stock Purchase Agreement  (the "Purchase
Agreement") dated February 18, 1998, by and among maker and Payee.

         Maker, and any endorser or guarantors of this Note and all other
persons who may become liable for all or any part of the obligations
represented by this Note, severally waive presentment for payment, protest,
notice of protest and of nonpayment, notice of intention to accelerate, and
notice of acceleration.

         In the event of default by Maker in the payment of any part of the
principal or interest on this Note when due and the continuance thereof for ten
(10) days following Maker's receipt of written notice of such default, the
entire unpaid balance of principal and accrued interest on this Note shall,
<PAGE>   2
at the option of the holder hereof, become immediately due and payable.
Failure by the holder to exercise any option upon one (1) default will not
constitute a waiver thereof or the waiver of the right to exercise such option
in the event of a subsequent default.  If after default this Note is placed in
the hands of an attorney for collection or is collected through judicial
proceedings, Maker shall pay, in addition to the sums referred to above, a
reasonable sum as collection or attorneys' fees and all other costs incurred by
the holder in collection of the unpaid amounts due hereunder.

         This note is made and is performable in Argyle, Denton County,Texas,
and Maker waives the right to be sued hereon elsewhere.  This Note shall be
governed by and construed in accordance with the laws of the State of Texas and
the applicable laws of the United States of America.

         IN WITNESS WHEREOF, the undersigned has executed this Note as of the
18th day of February, 1998.


                                        MAKER:

                                        Asesoria Garza Jasso, S.C.  
                                        A Mexican entity

                                        By:  /s/ Rafael Vaquero Bazan
                                            -----------------------------------
                                             Name:   Rafael Vaquero Bazan
                                                     An Authorized Officer
<PAGE>   3
Payment of the preceding promissory note is personally guaranteed by the
undersigned.


<TABLE>
<S>                                              <C>
 /s/ Rafael Vaquero Bazan                         /s/ Lorenzo Zambrano Trevino      
- -----------------------------------              -----------------------------------
Rafael Vaquero Bazan                             Lorenzo Zambrano Trevino
                                               
 /s/ Eduardo Vaquero Bazan                        /s/ Rafael J. Fco. Hernandez          
- -----------------------------------              -----------------------------------
Eduardo Vaquero Bazan                            Rafael J. Fco. Hernandez
                                               
 /s/ Carlos Vaquero Bazan                         /s/ Jorge Gutierrez Welsh              
- -----------------------------------              -----------------------------------
Carlos Vaquero Bazan                             Jorge Gutierrez Welsh
                                               
 /s/ Pedro Vaquero Bazan                          /s/ Pedro Garza Salazar                 
- -----------------------------------              -----------------------------------
Pedro Vaquero Bazan                              Pedro Garza Salazar
                                               
 /s/ Pedro Vaquero Garcia                         /s/ Pedro Villareal Lozano             
- -----------------------------------              -----------------------------------
Pedro Vaquero Garcia                             Pedro Villareal Lozano
                                               
 /s/ Jose Ma. Martinez Brohez                  
- ----------------------------------- 
Jose Ma. Martinez Brohez                       
                                               
 /s/ Frederico Martinez Brohez                 
- ----------------------------------- 
Frederico Martinez Brohez                      
                                               
 /s/ Jorge Martinez Brohez                     
- ----------------------------------- 
Jorge Martinez Brohez                          
                                               
 /s/ Fernando Camacho Casas                    
- ----------------------------------- 
Fernando Camacho Casas                         
                                               
 /s/ Enrique Portilla                          
- ----------------------------------- 
Enrique Portilla                               
                                               
 /s/ Francisco Domenech Tarrago                
- ----------------------------------- 
Francisco Domenech Tarrago                     
                                               
 /s/ Dr. David Madero Gonzalez                 
- ----------------------------------- 
Dr. David Madero Gonzalez                      
                                               
 /s/ Pedro Pierter Villarreal                  
- ----------------------------------- 
Pedro Pierter Villarreal                       
</TABLE>                                       
                                               

<PAGE>   1





                                                                      EXHIBIT 7C


                                PLEDGE AGREEMENT

         THIS PLEDGE AGREEMENT (this "Agreement"), dated as of February 18,
1998, between Asesoria Garza Jasso, S.C, a Mexican partnership (the "Pledgor"),
and Jorn Budde (the "Secured Party").

                              W I T N E S S E T H:

         WHEREAS, the Pledgor has entered into that certain Stock Purchase
Agreement dated as of February 18, 1998 (the "Purchase Agreement" certain
capitalized terms used herein which are defined in the Purchase Agreement shall
have the same meanings when used herein, unless otherwise defined herein) with
the Secured Party, pursuant to which, among other things, the Pledgor has
agreed to purchase and the Secured Party has agreed to sell to the Pledgor the
Shares and Pledgor has agreed to execute and deliver the Note; and

         WHEREAS, under the terms of the Purchase Agreement, that the Pledgor
has agreed to execute and deliver this Security Agreement and grant the
security interests contemplated hereby; and

         WHEREAS, this Agreement, the Purchase Agreement, and the Note are
hereinafter sometimes referred to as the "Loan Documents".

         NOW, THEREFORE, for good and valuable consideration the receipt of
which is hereby acknowledged by it, and in order to induce the Secured party to
sell the Shares, Pledgor agrees with the Secured Party, as follows:

                                   ARTICLE 1

                                  DEFINITIONS

         SECTION 1.1      Certain Terms.  The following terms (whether or not
underscored) when used in this Agreement, including its preamble and recitals,
shall have the following meanings (such definitions to be equally applicable to
the singular and plural forms thereof):

         "Collateral" is defined in Section 2.1.

         "Distributions" means all stock dividends, liquidating dividends,
shares of stock resulting from stock splits, reclassifications, warrants,
options, non-cash dividends and other distributions (whether similar or
dissimilar to the foregoing) on or with respect to any Pledged Shares or other
shares of capital stock constituting Collateral, but shall not mean Dividends.

         "Dividends" means cash dividends and cash distributions with respect
to any Pledged Shares made out of capital surplus.

         "Initial Pledged Shares" means the 200,000 shares of Common Stock of 
UniMark.




                                     -1-
<PAGE>   2

         "Pledged Property" means all Pledged Shares, and all other pledged
shares of capital stock, all other securities, all assignments of any amounts
due or to become due, all other instruments which are now being delivered by
the Pledgor to the Secured Party or may from time to time hereafter be
delivered by the Pledgor to the Secured Party for the purpose of pledge under
this Agreement or any other Loan Document, and all proceeds of any of the
foregoing.

         "Pledged Shares" means the Initial Pledged Shares and all other shares
of capital stock of  UniMark, if any, which are delivered by the Secured Party
as Pledged Property hereunder.

         "Pledgor" is defined in the preamble.

         "Purchase Agreement" is defined in the first recital.

         "Secured Obligations" is defined in Section 2.2.

         "U.C.C." means the Uniform Commercial Code as in effect in the State 
of Texas.

         "UniMark" means The UniMark group, Inc., a Texas corporation.


         SECTION 1.2      Purchase Agreement Definitions. Etc.  Unless
otherwise defined herein or the context otherwise requires, terms used in this
Agreement, including its preamble and recitals, have the meanings provided in
the Purchase Agreement.  References to the masculine gender shall include the
feminine and neuter  genders unless the context otherwise requires.

         SECTION 1.3      U.C.C. Definitions.  Unless otherwise defined herein
or the context otherwise requires, terms for which meanings are provided in the
U.C.C. are used in this Agreement, including its preamble and recitals, with
such meanings.


                                   ARTICLE 2

                                     PLEDGE

         SECTION 2.1      Grant of Security Interest.  Pledgor hereby pledges,
assigns, charges, mortgages, delivers and transfers to the Secured Party, and
hereby grants to the Secured Party, a continuing security interest in, all of
the following property (the "Collateral"):

         (a)     the Initial Pledged Shares;

         (b)     all Pledged Shares issued from time to time;

         (c)     all other Pledged Property, whether now or hereafter delivered
                 to the Secured Party in connection with this Agreement;





                                      -2-
<PAGE>   3

         (d)     all Dividends, Distributions, interest and other payments and
                 rights with respect to any Pledged Property; and

         (e)     all proceeds of any of the foregoing.

         SECTION 2.2      Security for Secured Obligations.  This Agreement
secures the payment in full of the Note, whether for principal, interest,
costs, fees, expenses or otherwise, and all obligations now or hereafter
existing (collectively, the "Secured Obligations").

         SECTION 2.3  Delivery of Pledged Property; Registration of Pledge,
Transfer, etc.  All certificates and Instruments representing or evidencing any
Collateral, including all Pledged Shares, shall be delivered to and held by or
on behalf of the Secured Party pursuant hereto, shall be in suitable form for
transfer by delivery, and shall be accompanied by all necessary Instruments of
transfer or assignment, duly executed in blank.

         SECTION 2.4      Continuing Security Interest; Transfer of Note.  This
                          Agreement shall

         (a)     create a continuing security interest in the Collateral;

         (b)     remain in full force and effect until payment in full of all
                 Secured Obligations;

         (c)     be binding upon Pledgor, its successors and assigns; provided
                 that Pledgor may not assign any of its rights or obligations
                 hereunder without the prior written consent of the Secured
                 Party; and

         (d)     inure to the benefit of the Secured Party and his heirs and
legal representatives.


                                   ARTICLE 3

                         REPRESENTATIONS AND WARRANTIES

         SECTION 3.1  Warranties, etc.  Pledgor represents and warrants unto
the Secured Party that as at the date of each pledge hereunder (including each
pledge of Pledged Shares) by Pledgor to the Secured Party of any Collateral,

         (a)     Pledgor has all requisite power and authority, and has taken
         all necessary corporate action, to execute and deliver and perform its
         obligations under this Pledge Agreement and to pledge the Collateral
         hereunder.

         (b)     Pledgor will be the legal and beneficial owner of, and will
         have good and marketable title to (and will have full right and
         authority to pledge and assign) all Collateral, free and clear of all
         Liens or other charges or encumbrances, except any Lien or security
         interest granted pursuant hereto in favor of the Secured Party.





                                      -3-
<PAGE>   4
         (c)     The delivery of the Collateral (including the delivery of the
         Initial Pledged Shares) to the Secured Party will be effective to
         create a valid, perfected, first priority security interest in such
         Collateral and all proceeds thereof, securing the Secured Obligations,
         and no filing or other action will be necessary to perfect or protect
         such security interest.

         (d)     In the case of any Pledged Shares constituting Collateral, all
         of such Pledged Shares will be duly authorized and validly issued,
         fully paid, and non-assessable.

                                   ARTICLE 4

                                   COVENANTS

         SECTION 4.1      Protect Collateral; Further Assurances. etc.  Pledgor
will not sell, assign, transfer, pledge or encumber in any other manner the
Collateral (except in favor of the Secured Party hereunder).  Pledgor will
warrant and will use its best efforts to defend the right and title herein
granted unto the Secured Party in and to the Collateral (and all right, title
and interest represented by the Collateral) against the claims and demands of
all Persons whomsoever.  Pledgor agrees that at any time, and from time to
time, at the expense of Pledgor, Pledgor will promptly execute and deliver all
further Instruments, and take all further action, that may be necessary or
desirable, or that the Secured Party may reasonably request, in order to
perfect and protect any security interest granted or purported to be granted
hereby or to enable the Secured Party to exercise and enforce its rights and
remedies hereunder with respect to any Collateral.

         SECTION 4.2      Stock Powers, etc.  Pledgor agrees that all Pledged
Shares (and all other shares of capital stock constituting Collateral)
delivered by Pledgor pursuant to this Agreement will be accompanied by duly
executed undated blank stock powers, or other equivalent Instruments of
transfer acceptable to the Secured Party.  Pledgor will, from time to time upon
the request of the Secured Party, promptly deliver to the Secured Party such
stock powers, Instruments and similar documents, satisfactory in form and
substance to the Secured Party, with respect to the Collateral as the Secured
Party may reasonably request and will, from time to time upon the request of
the Secured Party after the occurrence of any Default, promptly transfer any
Pledged Shares or other shares of Stock constituting Collateral into the name
of the Secured Party or any nominee designated by the Secured Party.

         SECTION 4.3      Continuous Pledge.  Pledgor will, at all times, keep
pledged to the Secured Party pursuant hereto all Pledged Shares and all other
shares of Stock constituting Collateral, all Dividends and Distributions with
respect thereto, and all other Collateral and other securities, instruments,
proceeds and rights from time to time received by or distributable to Pledgor
in respect of any Collateral.

         SECTION 4.4  Voting Rights; Dividends, etc.  Pledgor agrees to deliver
all Distributions at any time received by it to the Secured Party to be held as
Collateral hereunder and, in addition, to deliver (properly endorsed where
required hereby or requested by the Secured Party) to the Secured Party:





                                      -4-
<PAGE>   5
         (a)     after any Default shall have occurred and be continuing or if
         any Default shall occur as a result thereof, promptly upon receipt
         thereof by Pledgor and without any request therefor by the Secured
         Party, all Dividends, all other cash payments and all proceeds of the
         Collateral, all of which shall be held by the Secured Party as
         additional collateral; and

         (b)     after any Default shall have occurred and be continuing,
         promptly upon request of the Secured Party, such proxies and other
         documents as may be necessary to allow the Secured Party to exercise
         the voting power with respect to any share of capital stock
         constituting Collateral;

provided, however, that unless a Default shall have occurred and be continuing
or result therefrom, Pledgor shall be entitled to exercise, in its reasonable
judgment, but in a manner not inconsistent with the terms of the Purchase
Agreement or any other Loan Document (including this Agreement), the voting
power and all other incidental rights of ownership with respect to any Pledged
Shares or other shares of capital stock constituting Collateral (subject to
Pledgor's obligation to deliver to the Secured Party such Pledged Shares and
other shares in pledge hereunder).

All Dividends, Distributions, cash payments and proceeds which may at any time
and from time to time be held by Pledgor but which Pledgor is then obligated to
deliver to the Secured Party, shall, until delivery to the Secured Party, be
held by Pledgor separate and apart from its other property in trust for the
Secured Party.  The Secured Party agrees that unless a Default shall have
occurred and be continuing, the Secured Party shall, upon the written request
of Pledgor, promptly deliver such proxies and other documents, if any, as shall
be reasonably requested by Pledgor which are necessary to allow Pledgor to
exercise voting power with respect to any share of capital stock (including
Pledged Shares) constituting Collateral; provided, however that no vote shall
be cast, or consent, waiver or ratification given, or action taken by Pledgor
that would impair any Collateral or be inconsistent with or violate any
provision of the Purchase Agreement or any other Loan Document (including this
Agreement).


                                   ARTICLE 5

                                    REMEDIES

         SECTION 5.1      Actions upon Event of Default.  In addition to its
rights and remedies provided hereunder, whenever an Event of Default shall
occurred and be continuing, the Secured Party shall have all rights and
remedies of a secured party upon default under the U.C.C. or other applicable
law. Any notification required by law of any intended disposition by the
Secured Party of any of the Collateral shall be deemed reasonably and properly
given if given at least 15 days before such disposition.  Without limitation of
the above, the secured Party may, whenever an Event of Default shall have
occurred and be continuing, without prior notice to Pledgor, take all or any of
the following actions:

         (a)     transfer all or any part of the Collateral into the name of
         the Secured Party or its nominee, with or without disclosing that such
         Collateral is subject to the Lien and security interest hereunder;





                                      -5-
<PAGE>   6
         (b)     notify the parties obligated on any of the Collateral to make
         payment to the Secured Party of any amount due or to become due
         thereunder;

         (c)     enforce collection of any of the Collateral by suit or
         otherwise, and surrender, release or exchange all or any part thereof,
         or compromise or extend or renew for any period (whether or not longer
         than the original period) any obligations of any nature of any party
         with respect thereto;

         (d)     endorse any checks, drafts, or other writings in Pledgor's
         name to allow collection of the Collateral;

         (e)     take control of any proceeds of the Collateral; and

         (f)     execute (in the name, place and stead of Pledgor)
         endorsements, assignments, stock powers and other instruments of
         conveyance or transfer with respect to all or any of the Collateral.

         SECTION 5.2      Attorney-in-Fact. Pledgor hereby irrevocably appoints
the Secured Party its attorney-in-fact, with full authority in the place and
stead of Pledgor and in the name of Pledgor, the Secured Party, or otherwise,
from time to time in the Secured Party's discretion, to take any action and to
execute any Instrument which the Secured Party may deem necessary or advisable
to accomplish the purposes of this Agreement, including, upon the occurrence
and continuance of an Event of Default, all actions described in Section 5.1.

         SECTION 5.3      Private Sales.

         (a)     Pledgor recognizes that the Secured Party may be unable to
         effect a public sale of any or all the Pledged Shares by reason of
         certain prohibitions contained in the Securities Act of 1933, as
         amended (the "Securities Act") and applicable state securities laws or
         otherwise, and may be compelled to resort to one or more private sales
         thereof to a restricted group of purchasers that will be obliged to
         agree, among other things, to acquire such securities for their own
         account for investment and not with a view to the distribution or
         resale thereof.  Pledgor acknowledges and agrees that any such private
         sale may result in prices and other terms less favorable than if such
         sale were a public sale and, notwithstanding such circumstances,
         agrees that any such private sale shall be deemed to have been made in
         a commercially reasonable manner.  The Secured Party shall be under no
         obligation to delay sale of any of the Pledged Shares for the period
         of time necessary to permit the Pledgor to register such securities
         for public sale under the Securities Act, or under applicable state
         securities laws, even if UniMark would agree to do so.

         (b)     Pledgor further agrees to use its best efforts to do or cause
         to be done all such acts as may be necessary to make such sale or
         sales of all or any portion of the Pledged Shares pursuant to this
         Section 5.3 valid and binding and in compliance with any and all other
         applicable Requirements of Law.





                                      -6-
<PAGE>   7
                                   ARTICLE 6

                                 MISCELLANEOUS

         SECTION 6.1      Loan Document.  This Agreement is a Loan Document
executed pursuant to the Purchase Agreement and shall (unless otherwise
expressly indicated herein) be construed, administered and applied in
accordance with the terms and provisions thereof.

         SECTION 6.2      Amendments, etc.  No amendment or waiver of any
provision of this Agreement nor consent to any departure by Pledgor herefrom
shall in any event be effective unless the same shall be in writing, signed by
the Secured Party and then such waiver or consent shall be effective only in
the specific instance and for the specific purpose for which it is given.

         SECTION 6.3      Obligations Not Affected.  The obligations of Pledgor
under this Agreement shall remain in full force and effect without regard to,
and shall not be impaired or affected by:

         (a)     any amendment or modification or addition or supplement to the
         Purchase Agreement, any Note, any other Loan Document, any Instrument
         delivered in connection therewith or any assignment or transfer
         thereof;

         (b)     any exercise, non-exercise or waiver by the Secured Party of
         any right, remedy, power or privilege under or in respect of, or any
         release of any guaranty or collateral provided pursuant to, this
         Agreement, the Purchase Agreement, or any Loan Document;

         (c)     any waiver, consent, extension, indulgence or other action or
         inaction in respect of this Agreement, the Purchase Agreement or any
         Loan Document or any assignment or transfer of any thereof; or

         (d)     any bankruptcy, insolvency, reorganization, arrangement,
         readjustment, composition, liquidation or the like, death or
         incompetency of the Pledgor or any other Person, whether or not
         Pledgor shall have notice or knowledge of any of the foregoing.

         SECTION 6.4      Protection of Collateral.  The Secured Party may from
time to time, at its option, perform any act which Pledgor agrees hereunder to
perform and which Pledgor shall fail to perform after being requested in
writing to so perform (it being understood that no such request need be given
after the occurrence and during the continuance of a Default) and the Secured
Party may from time to time take any other action which the Secured Party
reasonably deems necessary for the maintenance, preservation or protection of
any of the Collateral or of its security interest therein.





                                      -7-
<PAGE>   8
         SECTION 6.5      Governing Law; Jurisdiction.

         (a)     THIS AGREEMENT SHALL BE DEEMED TO BE A CONTRACT MADE UNDER AND
GOVERNED BY THE INTERNAL LAWS OF THE STATE OF TEXAS.

         (b)     EACH PARTY TO THIS AGREEMENT HEREBY IRREVOCABLY SUBMITS TO THE
JURISDICTION OF ANY TEXAS STATE OR FEDERAL COURT SITTING IN DALLAS, TEXAS IN
ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT OR ANY
OTHER LOAN DOCUMENT OR RELATED DOCUMENT (AND PLEDGOR AGREES THAT SUCH
JURISDICTION WILL BE EXCLUSIVE WITH RESPECT TO CLAIMS BROUGHT BY PLEDGOR
AGAINST THE SECURED PARTY), AND EACH HEREBY IRREVOCABLY AGREES THAT ALL CLAIMS
IN RESPECT OF SUCH ACTION OR PROCEEDING MAY BE HEARD AND DETERMINED IN SUCH
TEXAS STATE OR FEDERAL COURT.  EACH PARTY TO THIS AGREEMENT HEREBY IRREVOCABLY
WAIVES, TO THE FULLEST EXTENT IT MAY EFFECTIVELY DO SO, THE DEFENSE OF ANY
INCONVENIENT FORUM TO THE MAINTENANCE OF SUCH ACTION OR PROCEEDING.

         (c)     Pledgor hereby irrevocably designates, appoints and empowers
Rafael Vaquero Bazan, as its authorized agent to receive, for and on its behalf
and on behalf of its property, service of process in the State of Texas when
and as such legal actions or proceedings may be brought in the courts of the
State of Texas or of the United States of America sitting in Texas, and such
service of process shall be deemed complete upon the date of delivery thereof
to such agent whether or not such agent gives notice thereof to Pledgor, or
upon the earliest of any other date permitted by applicable law.  It is
understood that a copy of said process served on such agent will as soon as
practicable be forwarded to Pledgor, at its address set forth below, but
Pledgor's failure to receive such copy shall not affect in any way the service
of said process on said agent as the agent of Pledgor.  Pledgor irrevocably
consents to the service of process out of any of the aforementioned courts in
any such action or proceeding by the mailing of the copies thereof by certified
mail, return receipt requested, postage prepaid, to Pledgor at its address set
forth below, such service to become effective upon the earlier of (i) the date
10 calendar days after such mailing or (ii) any earlier date permitted by
applicable law.  Pledgor agrees that it will at all times continuously maintain
an agent to receive service of process in the State of Texas and in the event
that, for any reason, the agent named above or its successor shall no longer
serve as its agent to receive service of process in the State of Texas on its
behalf, it shall promptly appoint a successor so to serve and shall advise the
Secured Party.





                                      -8-
<PAGE>   9
         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed as of the day and year first above written.


                                     ASESORIA GARZA JASSO, S.C
                                   
                                   
                                     By:   /s/ Rafael Vaquero Bazan         
                                     ------------------------------------------
                                     Rafael Vaquero Bazan, An Authorized Officer
                                   
                                   
                                   
                                          /s/ Jorn Budde
                                     ------------------------------------------
                                     Jorn Budde





                                      -9-


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