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                                                                   EXHIBIT 99.4




                          FIRST STOCK OPTION AGREEMENT

            FIRST STOCK OPTION AGREEMENT (this "First Option Agreement") dated
as of July 17, 1998, by and between M & M NOMINEE L.L.C., a Delaware limited
liability company ("Purchaser"), and THE UNIMARK GROUP, INC., a Texas
corporation (the "Company").

                              W I T N E S S E T H

            WHEREAS, the Board of Directors of Purchaser and the Board of
Directors of the Company have approved a Purchase Agreement dated as of even
date herewith (the "Purchase Agreement") providing for the issuance by the
Company and the purchase by Purchaser of shares of common stock, par value
$0.01 per share, of the Company (the "Common Stock");

            WHEREAS, to induce Purchaser to enter into the Purchase Agreement,
the Company has agreed to (i) grant to Purchaser an option pursuant to the
Second Option Agreement, by and between Purchaser and the Company, dated as of
the date hereof (the "Second Option Agreement"), and (ii) grant to Purchaser
the option set forth herein to purchase authorized but unissued shares of
Common Stock.

            NOW, THEREFORE, to induce Purchaser to enter into the Purchase
Agreement and in consideration of the premises herein contained, the parties
agree as follows:

1.       Definitions.  Capitalized terms used but not defined herein shall have
the same meanings as in the Purchase Agreement.

2.       Grant of Option.  Subject to the terms and conditions set forth
herein, the Company hereby grants to Purchaser an option (the "Option") to
purchase up to 1,000,000 authorized and unissued shares of Common Stock (the
"Option Shares"), at a price per share equal to $4.5375 (the "Exercise Price")
payable in cash as provided in Section 4 hereof.

3.       Exercise of Option.  (a)  Purchaser may exercise the Option, in whole
or in part, at any time or from time to time during the Exercise Period.  The
"Exercise Period" shall be the period from the date hereof until and including
the first anniversary of the date hereof.  Except as provided by the last
sentence of this Section 3(a), at 11:59 p.m.  (Dallas, TX time) on the last day
of the Exercise Period the Option, to the extent it shall not have been
exercised, shall terminate and be of no further force and effect.  If the
Option cannot be exercised prior to the first anniversary of the date hereof as
a result of any injunction, order or other legal restraint (each, a
"Restraint"), the Exercise Period shall terminate on the later of (i) the first
anniversary of the date hereof and (ii) the 10th business day after
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such Restraint shall have been dissolved or shall have become permanent and no
longer subject to appeal, as the case may be, but in no event later than 18
months after the date hereof.  If, at the end of the Exercise Period, such
Restraint shall not have been dissolved or otherwise resolved (to the
reasonable satisfaction of Purchaser) to allow the exercise of the Option,
then, upon written request made by Purchaser within 14 days of the end of the
Exercise Period, the Company shall redeem the Option for a redemption price
equal to (x) the excess of the Current Market Price (as defined in Section 6)
of the Common Stock as of the first anniversary of the date hereof over the
Exercise Price, multiplied by (y) the number of shares that would be issued
upon exercise of the Option but for the Restraint.

         (b)     Whenever Purchaser wishes to exercise the Option, it shall
deliver to the Company a written notice (the 'Notice", the date of receipt of
which being herein referred to as the "Notice Date") specifying (i) the total
number of shares it intends to purchase pursuant to such exercise, and (ii) a
place and date not earlier than two business days nor later than 60 calendar
days from the Notice Date for the closing of such purchase (a "Closing Date");
provided that if any closing of the purchase and sale pursuant to the Option (a
"Closing") cannot be consummated by reason of any applicable Law, the period of
time that otherwise would run from the Notice Date pursuant to this sentence
shall run instead from the date on which such restriction on consummation has
expired or been terminated; and provided further that, without limiting the
foregoing, if prior notification to or approval of any Governmental Authority
is required in connection with such purchase, Purchaser and, if applicable, the
Company shall promptly file the required notice or application for approval and
shall expeditiously process the same (and the Company shall cooperate with
Purchaser in the filing of any such notice or application and the obtaining of
any such approval), and the period of time that otherwise would run from the
Notice Date pursuant to this sentence shall run instead from the date on which,
as the case may be, (i) any required notification period has expired or been
terminated or (ii) such approval has been obtained, and in either event, any
requisite waiting period has passed.  If such notification period has not
expired or been terminated or such approval has not been obtained, or such
waiting period has not passed, in any case the effect of which is to prevent or
delay the Closing for 90 days beyond the Notice Date, then, upon written
request made by Purchaser within 14 days of the end of such 90 day period, the
Company shall redeem the Option for a redemption price equal to (x) the excess
of the Current Market Price of the Common Stock as of the first anniversary of
the date hereof over the Exercise Price, multiplied by (y) the number of shares
specified in the Notice.

         (c)     In connection with any Closing, the Company may request that
Purchaser represent that, as of the Closing Date applicable to such Closing,
(i) Purchaser is an "accredited investor" within the meaning of Rule 501 of the
Securities Act, and (ii) Purchaser is acquiring the Option Shares being
purchased at such Closing for the purpose of investment and not with a view to
or for sale in connection with any distribution thereof.  If the Company makes
such a request and Purchaser fails to make


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such representations, then (except as provided in the following sentence) the
Company shall have no obligation to effect such Closing.  Purchaser may, in
lieu of making the representation set forth in clause (i), furnish the Company
with an opinion of counsel reasonably acceptable to the Company, to the effect
that the acquisition of the Option Shares at such Closing is exempt from
registration under the Securities Act and applicable state securities laws.
Notwithstanding the foregoing purchaser shall not be required to make the
representation set forth in clause (i) or furnish such a legal opinion if
purchaser is exercising the Option and immediately thereafter selling the
Option Shares pursuant to the Registration Rights Agreement.

4.       Payment and Delivery of Certificates.  (a) At each Closing, Purchaser
shall pay to the Company the aggregate Exercise Price for the Option Shares
purchased at such Closing pursuant to the exercise of the Option in immediately
available funds by wire transfer to a bank account designated not later than
one business day prior to the Closing Date for such Closing by the Company.

         (b)     At such Closing, simultaneously with the delivery of the
aggregate Exercise Price as provided in Section 4(a) hereof, the Company shall
deliver to Purchaser a certificate or certificates representing the number of
Option Shares then being purchased by Purchaser, registered in the name of
Purchaser or as designated in writing by Purchaser, which Option Shares shall
be fully paid and nonassessable and free and clear of all liens, claims,
charges and encumbrances of any kind whatsoever.

         (c)     If at the time of issuance of any Option Shares pursuant to
any exercise of the Option, the Company shall have issued any share purchase
rights or similar securities ("Rights") to holders of any class of the Common
Stock, then each such Option Share shall also represent Rights with terms
substantially the same as and at least as favorable to Purchaser as those
issued to other holders of the Common Stock.

         (d)     Certificates for Option Shares delivered at any Closing
hereunder shall be endorsed with a restrictive legend, which shall read
substantially as follows:

            "The securities represented by this certificate have not been
            registered under the Securities Act of 1933 or the securities laws
            of any state and may not be sold or otherwise disposed of except
            pursuant to an effective registration statement under such act and
            applicable state securities laws or an applicable exemption to the
            registration requirements of such act or such laws."

It is understood and agreed that the above legend shall be removed by delivery
of substitute certificate(s) without such legend in connection with a transfer
or sale if (i) the Company has been furnished with an opinion of counsel,
reasonably satisfactory to counsel for the Company, that such transfer or sale
will not violate the Securities Act or





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applicable securities laws of any state or (ii) such transfer or sale shall
have been registered and qualified pursuant to the Securities Act and any
applicable state securities laws.

5.       Representations and Warranties; Covenants.  (a) The Company hereby
represents and warrants to Purchaser that: (i) the Company has full corporate
right, power and authority to execute and deliver this First Option Agreement
and to perform all of its obligations hereunder; (ii) such execution, delivery
and performance have been duly authorized by the Board of Directors of the
Company, and no other corporate proceedings are necessary therefor; (iii) this
First Option Agreement has been duly and validly executed and delivered by the
Company and represents a valid and legally binding obligation of the Company,
enforceable against the Company in accordance with its terms; and (iv) the
Company has taken all necessary corporate action to authorize and reserve and
permit it to issue, and at all times from the date hereof through the date of
the exercise in full or the expiration or termination of the Option, shall have
reserved for issuance upon exercise of the Option, 1,000,000 shares of Common
Stock (subject to adjustment as provided herein), all of which, upon issuance
in accordance with the terms of this First Option Agreement, shall be duly
authorized, validly issued, fully paid and nonassessable, shall be delivered
free and clear of all claims, liens, encumbrances and security interests and
not subject to any preemptive rights of any stockholder of the Company, and
will be eligible for NASDAQ NMS trading without further consents or actions
(other than registration thereof pursuant to the Registration Rights
Agreement).

         (b)     Purchaser hereby represents and warrants to the Company that
(i) Purchaser has full corporate right, power and authority to execute and
deliver this First Option Agreement and to perform all of its obligations
hereunder; (ii) such execution, delivery and performance have been duly
authorized by all requisite corporate action by Purchaser, and no other
corporate proceedings are necessary therefor; (iii) this First Option Agreement
has been duly and validly executed and delivered by Purchaser and represents a
valid and legally binding obligation of Purchaser, enforceable against
Purchaser in accordance with its terms; and (iv) any Common Stock acquired by
Purchaser upon exercise of the Option will not be transferred or otherwise
disposed of for one year from the date hereof and then only in compliance with
the Securities Act.

6.       Adjustment upon Changes in Capitalization.  (a)  In the event of any
change in the Common Stock by reason of stock dividends, stock splits,
recapitalizations or the like, the type and number of shares subject to the
Option and the Exercise Price shall be adjusted appropriately.

         (b)     If at any time following the date hereof, the Company shall
issue shares of Common Stock (or rights, warrants or other securities
convertible into or exchangeable for shares of Common Stock (collectively
"Convertible Securities")) at a price per share





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(or having a conversion price per share) less than the Current Market Price (as
defined below) per share of Common Stock as of the date of issuance of such
shares (or, in the case of Convertible Securities, less than the Current Market
Price as of the date of issuance of the Convertible Securities in respect of
which shares of Common Stock were issued), then the Exercise Price shall be
adjusted by multiplying (A) the Exercise Price in effect on the day immediately
prior to such date by (B) a fraction, the numerator of which shall be the sum
of (1) the number of shares of Common Stock outstanding on such date and (2)
the number of shares of Common Stock purchasable at the then Current Market
Price per share with the aggregate consideration receivable by the Company for
the total number of shares of Common Stock so issued (or into which the
Convertible Securities may convert), and the denominator of which shall be the
sum of (x) the number of shares of Common Stock outstanding on such date and
(y) the number of additional shares of Common Stock issued (or into which the
Convertible Securities may convert).

         An adjustment made pursuant to this Section 6(b) shall be made on the
next business day following the date on which any such issuance is made and
shall be effective retroactively to the close of business on the date of such
issuance.  For purposes of this Section 6(b), the aggregate consideration
receivable by the Company in connection with the issuance of shares of Common
Stock or of Convertible Securities shall be deemed to be equal to the sum of
the aggregate offering price (before deduction of underwriting discounts or
commissions and expenses payable to third parties) of all such Common Stock and
Convertible Securities plus the minimum aggregate amount, if any, payable upon
exercise or conversion of any such Convertible Securities.  The issuance or
reissuance of any shares of Common Stock (whether treasury shares or newly
issued shares) pursuant to (i) a dividend or distribution on, or subdivision,
combination or reclassification of, the outstanding shares of Common Stock
requiring an adjustment in the Exercise Price pursuant to Section 6(a), or (ii)
any stock option plan, stock purchase plan or other benefit program of the
Company or executive compensation package approved by the Company's Board of
Directors involving the grant of options to employees or directors of the
Company shall not be deemed to constitute an issuance of Common Stock or
Convertible Securities by the Company to which this Section 6(b) applies.  Upon
the expiration unexercised of any Convertible Securities for which an
adjustment has been made pursuant to this Section 6(b), the adjustments shall
forthwith be reversed to effect such rate of conversion as would have been in
effect at the time of such expiration or termination had such Convertible
Securities, to the extent outstanding immediately prior to such expiration or
termination, never been issued.

         "Current Market Price", when used with reference to shares of the
Common Stock or another security on any date, shall mean the average of the
daily closing prices per share of such Common Stock or other security for the
20 preceding trading days.  If the Common Stock or such other securities are
listed or admitted to trading on a national securities exchange, the closing
price shall be the last sale price, regular way, or, in case





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no such sale takes place on such day, the average of the closing bid and asked
prices, regular way, in either case as reported in the principal consolidated
transaction reporting system with respect to securities listed or admitted to
trading on the New York Stock Exchange or, if the Common Stock or such other
securities are not listed or admitted to trading on the New York Stock
Exchange, as reported in the principal consolidated transaction reporting
system with respect to securities listed on the principal national securities
exchange on which the Common Stock or such other securities are listed or
admitted to trading or, if the Common Stock or such other securities are not so
listed on any national securities exchange, as reported in the transaction
reporting system applicable to securities designated as a "national market
system security" or NASDAQ.  If the Common Stock or such other securities are
not publicly held or so listed or designated, "Current Market Price" shall mean
the Fair Market Value (as defined below) per share of Common Stock or of such
other securities as determined in good faith by the Board of Directors of the
Company based on an opinion of an independent investment banking firm with an
established national reputation with respect to the valuation of securities.

         "Fair Market Value" shall mean, as to shares of Common Stock or any
other securities of the Company or any other issuer which are publicly traded,
the Current Market Prices of such shares or securities.  The "Fair Market
Value" of any security which is not publicly traded or of any other property
shall mean the fair value thereof as determined by an independent investment
banking or appraisal firm experienced in the valuation of such securities or
property selected in good faith by the Board of Directors of the Company.

         (c)     In case the Company shall at any time or from time to time
after the date hereof declare, order, pay or make a dividend or other
distribution (including, without limitation, any distribution of stock or other
securities or property or Convertible Securities of the Company or any of its
Subsidiaries by way of dividend or spinoff), on its Common Stock, then, and in
each such case, the Exercise Price shall be adjusted by multiplying (1) the
applicable Exercise Price on the day immediately prior to the record date fixed
for the determination of stockholders entitled to receive such dividend or
distribution by (2) a fraction, the numerator of which shall be the Current
Market Price of the Common Stock less the Fair Market Value of such dividend or
distribution (per share of Common Stock), and the denominator of which shall be
such average Current Market Price of the Common Stock.  If any dividend or
distribution is declared or ordered and a Closing Date is before the record
date for such dividend or distribution, then no adjustment in respect thereof
shall be made to the Exercise Price with respect to the Option Shares acquired
on such Closing Date.

         (d)     For purposes of this Section 6, the number of shares of Common
Stock at any time outstanding shall not include any shares of Common Stock then
owned or held by or for the account of the Company.





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         (e)     The term "dividend," as used in this Section 6, shall mean a
dividend or other distribution in respect of shares of Common Stock of the
Company.

         (f)     Anything in this Section 6 to the contrary notwithstanding,
the Company shall not be required to give effect to any adjustment in the
Exercise Price unless and until the net effect of one or more adjustments (each
of which shall be carried forward), determined as above provided, shall have
resulted in a change of the Exercise Price by at least one percent, and when
the cumulative net effect of more than one adjustment so determined shall be to
change the Exercise Price by at least one percent, such change in Exercise
Price shall thereupon be given effect.

         (g)     The certificate of any firm of independent public accountants
of recognized national standing selected by the Board of Directors of the
Company (which may be the firm of independent public accountants regularly
employed by the Company) shall be presumptively correct for any computation
made under this Section 6.

7.       Registration Rights.  Contemporaneously herewith, Purchaser and the
Company are entering into a Registration Rights Agreement providing for
registration of the Option Shares.

8.       Listing.  If the Common Stock or any other securities to be acquired
upon exercise of the Option are then listed on any national securities
exchange, the Company, upon the request of Purchaser, will promptly file an
application to list the Option Shares or other securities to be acquired upon
exercise of the Option on all such exchanges and will use its best efforts to
obtain approval of such listings as soon as practicable.

9.       Survival.  The representations, warranties, covenants and agreements of
the parties hereto shall survive any Closing.

10.      Severability.  Any term, provision, covenant or restriction contained 
in this First Option Agreement held by a court or other Governmental Authority
of competent jurisdiction to be invalid, void or unenforceable shall be
ineffective to the extent of such invalidity, voidness or unenforceability, but
neither the remaining terms, provisions, covenants or restrictions contained in
this First Option Agreement nor the validity or enforceability thereof in any
other jurisdiction shall be affected or impaired thereby.  Any term, provision,
covenant or restriction contained in this First Option Agreement that is so
found to be so broad as to be unenforceable shall be interpreted to be as broad
as is enforceable.

11.      Entire Agreement.  This First Option Agreement, the Second Option
Agreement, the Purchase Agreement (including the documents and the instruments
referred to therein or delivered in connection therewith) and the Registration
Rights Agreement constitute the entire agreement between the parties and
supersede all prior agreements and





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understandings, agreements or representations by or between the parties,
written and oral, with respect to the subject matter hereof and thereof.

12.      Successors; No Third Party Beneficiaries.  The terms and conditions of
this First Option Agreement shall inure to the benefit of and be binding upon
the parties hereto and their respective successors and assigns.  Nothing in
this First Option Agreement, expressed or implied, is intended to confer upon
any party, other than the parties hereto, and their respective successors and
assigns, any rights, remedies, obligations, or liabilities under or by reason
of this First Option Agreement, except as expressly provided herein.

13.      Notices.  All notices or other communications which are required or
permitted hereunder shall be in writing and sufficient if delivered in
accordance with Section 8.5 of the Purchase Agreement (which is incorporated
herein by reference).

14.      Further Assurances.  In the event of any exercise of the Option by
Purchaser, the Company and Purchaser shall execute and deliver all other
documents and instruments and take all other action that may be reasonably
necessary in order to consummate the transactions provided for by such
exercise.

15.      Specific Performance.  The parties hereto agree that if for any reason
Purchaser or the Company shall have failed to perform its obligations under
this First Option Agreement, then either party hereto seeking to enforce this
First Option Agreement against such non-performing party shall be entitled to
specific performance and injunctive and other equitable relief, and the parties
hereto further agree to waive any requirement for the securing or posting of
any bond in connection with the obtaining of any such injunctive or other
equitable relief.  This provision is without prejudice to any other rights that
either party hereto may have against the other party hereto for any failure to
perform its obligations under this First Option Agreement.

16.       Governing Law.  This First Option Agreement shall be governed by the
laws of the State of Delaware, without giving effect to the conflict of laws
principles thereof.  Each party hereby irrevocably and unconditionally consents
to submit to the exclusive jurisdiction of the courts of the State of Delaware
and of the United States of America located in Wilmington, Delaware, for any
Litigation (and agrees not to commence any Litigation except in any such
court).  Each party hereby irrevocably and unconditionally waives any objection
to the laying of venue of any Action in the courts of the State of Delaware or
of the United States of America located in Wilmington, Delaware, and hereby
further irrevocably and unconditionally waives and agrees not to plead or claim
in any such court that any Action brought in any such court has been brought in
an inconvenient forum.





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17.      Regulatory Approvals; Section 16(b).  If, in connection with the
exercise of the Option under Section 3, prior notification to or approval of
any Governmental Authority is required, then the required notice or application
for approval shall be promptly filed and/or expeditiously processed by the
Company and periods of time that otherwise would run pursuant hereto (if any)
shall run instead from the date on which any such required notification period
has expired or been terminated or such approval has been obtained, and in
either event, any requisite waiting period shall have passed.  Periods of time
that otherwise would run pursuant to this First Option Agreement shall also be
extended to the extent necessary in order to avoid liability under Section
16(b) of the Exchange Act.

18.      Waiver and Amendment.  Any provision of this First Option Agreement
may be waived in writing at any time by the party that is entitled to the
benefits of such provision.  This First Option Agreement may not be modified,
amended, altered or supplemented except upon the execution and delivery of a
written agreement executed by the parties hereto.





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            IN WITNESS WHEREOF, each of the parties hereto has executed this
First Option Agreement as of the date first written above.

                                       PURCHASER:

                                       M & M NOMINEE L.L.C.


                                       By:    /s/ Peter Streinger
                                             ------------------------------
                                             Name:   Peter Streinger
                                             Title:  Manager


                                       THE COMPANY:

                                       THE UNIMARK GROUP, INC.


                                       By:    /s/ Rafael Vaquero Bazan
                                             ------------------------------
                                             Name:   Rafael Vaquero Bazan
                                             Title:  President, Chief Executive
                                                     Officer and Chief
                                                     Operating Officer






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