<PAGE>


                                                                   EXHIBIT 10.10

                                                                  EXECUTION COPY


                              SUBSIDIARY GUARANTY

                        Dated as of September 30, 1999

                                     From

               THE PERSONS LISTED ON THE SIGNATURE PAGES HEREOF

                           as Subsidiary Guarantors


                                  in favor of

                      THE SECURED PARTIES REFERRED TO IN
                    THE CREDIT AGREEMENT REFERRED TO HEREIN

<PAGE>


                               TABLE OF CONTENTS
                               -----------------

<TABLE>
<CAPTION>
Section                                                                    Page
<S>                                                                        <C>
SECTION 1.   SUBSIDIARY GUARANTY; LIMITATION OF LIABILITY                     1
SECTION 2.   SUBSIDIARY GUARANTY ABSOLUTE
SECTION 3.   WAIVERS AND ACKNOWLEDGMENTS
SECTION 4.   SUBROGATION
SECTION 5.   PAYMENTS FREE AND CLEAR OF TAXES, ETC
SECTION 6.   REPRESENTATIONS AND WARRANTIES
SECTION 7.   COVENANTS
SECTION 8.   AMENDMENTS, ETC
SECTION 9.   NOTICES, ETC
SECTION 10.  NO WAIVER; REMEDIES
SECTION 11.  RIGHT OF SET-OFF
SECTION 12.  CONTINUING SUBSIDIARY GUARANTY; ASSIGNMENTS UNDER
             THE CREDIT AGREEMENT
SECTION 13.  EXECUTION IN COUNTERPARTS
</TABLE>

<PAGE>


<TABLE>
<S>                                                                          <C>
SECTION 14.  GOVERNING LAW; JURISDICTION; WAIVER OF JURY TRIAL, ETC          11
</TABLE>

<PAGE>


                                 SUBSIDIARY GUARANTY


          SUBSIDIARY GUARANTY dated as of September 30, 1999 made by the Persons
listed on the signature pages hereof under the caption "Subsidiary Guarantors"
(together with the Additional Subsidiary Guarantors as defined in Section 8(b),
each a "Subsidiary Guarantor"), in favor of the Secured Parties (as defined in
        --------------------
the Credit Agreement referred to below).

          PRELIMINARY STATEMENT.  The Lender Parties and Banque Nationale de
Paris, as Agent for the Lender Parties, are parties to a Credit Agreement dated
as of September 30, 1999 (said Agreement, as it may hereafter be amended,
supplemented or otherwise modified from time to time, being the "Credit
                                                                 ------
Agreement"; the terms defined therein and not otherwise defined herein being
---------
used herein as therein defined) with Better Minerals & Aggregates Company, a
Delaware corporation formerly known as "USS Intermediate Holdco, Inc." (the
"Borrower"), BMAC Holdings, Inc., a Delaware corporation, and George F. Pettinos
(Canada) Limited, a corporation organized and existing under the laws of
Ontario, Canada. Each Subsidiary Guarantor may receive a portion of the proceeds
of the Advances under the Credit Agreement and will derive substantial direct
and indirect benefit from the transactions contemplated by the Credit Agreement.
It is a condition precedent to the making of Advances and Drawings and the
issuance of Letters of Credit by the Lender Parties under the Credit Agreement
and the entry by the Hedge Banks into Bank Hedge Agreements with the Loan
Parties from time to time that each Subsidiary Guarantor shall have executed and
delivered this Subsidiary Guaranty.

          NOW, THEREFORE, in consideration of the premises and in order to
induce the Lender Parties to make Advances and Drawings and to issue Letters of
Credit under the Credit Agreement and the Hedge Banks to enter into Bank Hedge
Agreements with the Loan Parties from time to time, each Subsidiary Guarantor,
jointly and severally with each other Subsidiary Guarantor, hereby agrees as
follows:

          SECTION 1.  Subsidiary Guaranty; Limitation of Liability. (a)  Each
                      --------------------------------------------
Subsidiary Guarantor hereby unconditionally and irrevocably guarantees the
punctual payment when due, whether at stated maturity, by acceleration or
otherwise, of all Obligations of each other Loan Party now or hereafter existing
under the Loan Documents, whether for principal, interest, fees, expenses or
otherwise (such Obligations being the "Guaranteed Obligations"). Without
                                       ----------------------
limiting the generality of the foregoing, each Subsidiary Guarantor's liability
shall extend to all amounts that constitute part of the Guaranteed Obligations
and would be owed by any Loan Party to the Agent or any other Secured Party
under the Loan Documents but for the fact that they are unenforceable or not
allowable due to the existence of a bankruptcy, reorganization or similar
proceeding involving such Loan Party.

          (b) (i)  Each Subsidiary Guarantor and by the Agent's acceptance of
this Subsidiary Guaranty, the Agent and each other Secured Party, hereby
confirms that it is the
<PAGE>

intention of all such parties that this Subsidiary Guaranty not constitute a
fraudulent transfer or conveyance for purposes of Bankruptcy Law, the Uniform
Fraudulent Conveyance Act, the Uniform Fraudulent Transfer Act or any similar
federal or state law to the extent applicable to this Subsidiary Guaranty. To
effectuate the foregoing intention, the Agent, the other Secured Parties and the
Subsidiary Guarantors hereby irrevocably agree that the Obligations of each
Subsidiary Guarantor under this Subsidiary Guaranty shall not exceed the greater
of (A) the net benefit realized by such Subsidiary Guarantor from the proceeds
of the Advances and Drawings made from time to time by the Borrower and the
Canadian Borrower, respectively, to such Subsidiary Guarantor or any subsidiary
of such Subsidiary Guarantor and (B) the maximum amount that will, after giving
effect to such maximum amount and all other contingent and fixed liabilities of
such Subsidiary Guarantor that are relevant under such laws, and after giving
effect to any collections from, rights to receive contribution from or payments
made by or on behalf of any other Subsidiary Guarantor in respect of the
Obligations of such other Subsidiary Guarantor under this Subsidiary Guaranty,
result in the Obligations of such Subsidiary Guarantor under this Subsidiary
Guaranty not constituting a fraudulent transfer or conveyance. For purposes
hereof, "Bankruptcy Law" means Title 11, U.S. Code, or any similar Federal or
         --------------
state law for the relief of debtors.

          (ii)  Each Subsidiary Guarantor agrees that in the event any payment
shall be required to be made to the Secured Parties under this Subsidiary
Guaranty or any other guaranty, such Subsidiary Guarantor will contribute, to
the maximum extent permitted by law, such amounts to each other Subsidiary
Guarantor and each other guarantor so as to maximize the aggregate amount paid
to the Secured Parties under the Loan Documents.

     SECTION 2.  Subsidiary Guaranty Absolute .  Each Subsidiary Guarantor
                 ----------------------------
guarantees that the Guaranteed Obligations will be paid strictly in accordance
with the terms of the Loan Documents, regardless of any law, regulation or order
now or hereafter in effect in any jurisdiction affecting any of such terms or
the rights of the Agent or any other Secured Party with respect thereto (but
subject, however, to the provisions of Section 1 hereof).  The Obligations of
each Subsidiary Guarantor under this Subsidiary Guaranty are independent of the
Guaranteed Obligations or any other Obligations of any other Loan Party under
the Loan Documents, and a separate action or actions may be brought and
prosecuted against such Subsidiary Guarantor to enforce this Subsidiary
Guaranty, irrespective of whether any action is brought against the Borrower or
any other Loan Party or whether the Borrower or any other Loan Party is joined
in any such action or actions.  The liability of each Subsidiary Guarantor under
this Subsidiary Guaranty shall be irrevocable, absolute and unconditional
irrespective of, and each Subsidiary Guarantor hereby irrevocably waives to the
fullest extent it may legally and effectively do so any defenses it may now or
hereafter have in any way relating to, any or all of the following:

     (a) any lack of validity or enforceability of any Loan Document or any
agreement or instrument relating thereto;

     (b) any change in the time, manner or place of payment of, or in any other
term of, all or any of the Guaranteed Obligations or any other Obligations of
any other Loan Party under the Loan Documents, or any other amendment or waiver
of or any consent to departure from any Loan Document, including, without
limitation, any increase in the Guaranteed Obligations
<PAGE>

resulting from the extension of additional credit to any Loan Party or any of
its Subsidiaries or otherwise;

     (c) any taking, exchange, release or non-perfection of any Collateral, or
any taking, release or amendment or waiver of or consent to departure from any
other guaranty, for all or any of the Guaranteed Obligations;

     (d) any manner of application of Collateral, or proceeds thereof, to all or
any of the Guaranteed Obligations, or any manner of sale or other disposition of
any Collateral for all or any of the Guaranteed Obligations or any other
Obligations of any other Loan Party under the Loan Documents or any other assets
of any Loan Party or any of its Subsidiaries;

     (e) any change, restructuring or termination of the corporate structure or
existence of any Loan Party or any of its Subsidiaries;

     (f) any failure of any Secured Party to disclose to such Subsidiary
Guarantor or any other Loan Party any information relating to the financial
condition, operations, properties or prospects of any other Loan Party now or in
the future known to any Secured Party (such Subsidiary Guarantor waiving any
duty on the part of the Secured Parties to disclose such information); or

     (g) any other circumstance (including, without limitation, any statute of
limitations) or any existence of or reliance on any representation by the Agent
or any other Secured Party that might otherwise constitute a defense available
to, or a discharge of, the Borrower, any Subsidiary Guarantor, any other Loan
Party or any other guarantor or surety.

This Subsidiary Guaranty shall continue to be effective or be reinstated, as the
case may be, if at any time any payment of any of the Guaranteed Obligations is
rescinded or must otherwise be returned by any Secured Party or any other Person
upon the insolvency, bankruptcy or reorganization of the Borrower or any other
Loan Party or otherwise, all as though such payment had not been made.

     SECTION 3.  Waivers and Acknowledgments.  (a)  Each Subsidiary Guarantor
                 ---------------------------
hereby waives promptness, diligence, notice of acceptance and any other notice
with respect to any of the Guaranteed Obligations and this Subsidiary Guaranty
and any requirement that the Agent or any other Secured Party protect, secure,
perfect or insure any Lien or any property subject thereto or exhaust any right
or take any action against any Loan Party or any other Person or any Collateral.

     (b) Each Subsidiary Guarantor hereby waives any right to revoke this
Subsidiary Guaranty, and acknowledges that this Subsidiary Guaranty is
continuing in nature and applies to all Guaranteed Obligations, whether existing
now or in the future.

     (c) Each Subsidiary Guarantor acknowledges that the Agent may, without
notice to or demand upon such Subsidiary Guarantor and without affecting the
liability of such Subsidiary Guarantor under this Subsidiary Guaranty, foreclose
under any Mortgage by nonjudicial sale, and such Subsidiary Guarantor hereby
waives any defense to the recovery by the Agent and the
<PAGE>

other Secured Parties against such Subsidiary Guarantor of any deficiency after
such nonjudicial sale and any defense or benefits that may be afforded by
applicable law.

     (d) Each Subsidiary Guarantor acknowledges that it will receive substantial
direct and indirect benefits from the financing arrangements contemplated by the
Loan Documents and that the waivers set forth in this Section 3 are knowingly
made in contemplation of such benefits.

     SECTION 4.  Subrogation.  No Subsidiary Guarantor will exercise any rights
                 -----------
that it may now or hereafter acquire against any Loan Party or any other insider
guarantor that arise from the existence, payment, performance or enforcement of
such Subsidiary Guarantor's Obligations under this Subsidiary Guaranty or any
other Loan Document, including, without limitation, any right of subrogation,
reimbursement, exoneration, contribution or indemnification and any right to
participate in any claim or remedy of the Agent or any other Secured Party
against any Loan Party or any other insider guarantor or any Collateral, whether
or not such claim, remedy or right arises in equity or under contract, statute
or common law, including, without limitation, the right to take or receive from
any Loan Party or any other insider guarantor, directly or indirectly, in cash
or other property or by set-off or in any other manner, payment or security on
account of such claim, remedy or right, unless and until all of the Obligations
constituting an Advance or Drawing and all other Guaranteed Obligations or
amounts payable under this Subsidiary Guaranty shall have been paid in full in
cash, all Bank Hedge Agreements shall have expired or terminated and the
Commitments shall have expired or terminated.  If any amount shall be paid to
any Subsidiary Guarantor in violation of the preceding sentence at any time
prior to the later of the payment in full in cash of the Guaranteed Obligations
and all other amounts payable under this Subsidiary Guaranty and the later of
(i) the Termination Date and (ii) the expiration or termination of all Bank
Hedge Agreements, such amount shall be held in trust for the benefit of the
Agent and the other Secured Parties and shall forthwith be paid to the Agent to
be credited and applied to the Guaranteed Obligations and all other amounts
payable under this Subsidiary Guaranty, whether matured or unmatured, in
accordance with the terms of the Loan Documents.  If (i) any Subsidiary
Guarantor shall make payment to the Agent or any other Secured Party of all or
any part of the Guaranteed Obligations, (ii) all of the Obligations and
constituting an Advance or Drawing and all other Guaranteed Obligations payable
under this Subsidiary Guaranty shall be paid in full in cash and (iii) the
Termination Date shall have occurred and all Bank Hedge Agreements shall have
expired or terminated, the Agent and the other Secured Parties will, at such
Subsidiary Guarantor's request and expense, execute and deliver to such
Subsidiary Guarantor appropriate documents, without recourse and without
representation or warranty, necessary to evidence the transfer by subrogation to
such Subsidiary Guarantor of an interest in the Guaranteed Obligations resulting
from such payment by such Subsidiary Guarantor.

     SECTION 5.  Payments Free and Clear of Taxes, Etc .  (a)  Any and all
                 -------------------------------------
payments by the Subsidiary Guarantors hereunder shall be made, in accordance
with Section 2.14 of the Credit Agreement, free and clear of and without
deduction or withholding for any and all Taxes. If any Subsidiary Guarantor
hereunder shall be required by law to deduct any Taxes from or in respect of any
sum payable hereunder to any Lender Party or the Agent, (i) the sum payable
shall be increased as may be necessary so that after making all required
deductions or withholdings (including deductions applicable to additional sums
payable under this Section 5) such Lender Party or the Agent (as the case may
be) receives an amount equal to the sum it would have
<PAGE>

received had no such deductions or withholdings been made, (ii) such Subsidiary
Guarantor shall make such deductions or withholdings and (iii) such Subsidiary
Guarantor shall pay the full amount deducted to the relevant taxation authority
or other authority in accordance with applicable law.

     (b) In addition, each Subsidiary Guarantor shall pay any Other Taxes.

     (c) Each Subsidiary Guarantor shall indemnify each Lender Party and the
Agent for the full amount of Taxes and Other Taxes (including, without
limitation, any Taxes or Other Taxes imposed by any jurisdiction on amounts
payable under this Section), paid by such Lender Party or the Agent (as the case
may be) and any liability (including penalties, additions to tax, interest and
expenses) arising therefrom or with respect thereto.  This indemnification shall
be made within 30 days from the date such Lender Party or the Agent (as the case
may be) makes written demand therefor and provides such Subsidiary Guarantor
with evidence of such liability reasonably satisfactory to such Subsidiary
Guarantor.

     (d) Within 30 days after the date of any payment of Taxes, such Subsidiary
Guarantor shall furnish to the Agent, at its address referred to in Section 8.02
of the Credit Agreement, the original receipt of payment thereof, a certified
copy of such receipt or other evidence of payment reasonably acceptable to the
Agent.  In the case of any payment hereunder by or on behalf of such Subsidiary
Guarantor through an account or branch outside the United States or on behalf of
such Subsidiary Guarantor by a payor that is not a United States person, if such
Subsidiary Guarantor determines that no Taxes are payable in respect thereof,
such Subsidiary Guarantor shall furnish, or shall cause such payor to furnish,
to the Agent, at such address, an opinion of counsel acceptable to the Agent
stating that such payment is exempt from Taxes.  For purposes of this subsection
(d) and subsection (e), the terms "United States" and "United States person"
                                   -------------       --------------------
shall have the meanings specified in Section 7701 of the Internal Revenue Code.

     (e) Each Lender Party organized under the laws of a jurisdiction outside
the United States shall, on or prior to the date of its execution and delivery
of the Credit Agreement in the case of each Initial Lender or the Initial
Issuing Bank, as the case may be, and on the date of the Assignment and
Acceptance pursuant to which it became a Lender Party in the case of each other
Lender Party, and from time to time thereafter if requested in writing by any
Subsidiary Guarantor or the Agent (but only so long thereafter as such Lender
Party remains lawfully able to do so and in any event prior to the date of the
first payment to such Lender Party hereunder), provide the Agent and such
Subsidiary Guarantor with two duly completed and executed copies of Internal
Revenue Service (the "IRS") Form 1001 or 4224, as appropriate, or any successor
                      ---
form prescribed by the IRS, certifying (if it is the case) that such Lender
Party is exempt from or is entitled to a reduced rate of United States
withholding tax on payments pursuant to this Subsidiary Guaranty or to the
extent permitted by law, as an alternative to such Form 1001 or 4224, each such
Lender Party may provide such Subsidiary Guarantor and the Agent with two duly
completed and executed copies of IRS Form W-8, or any successor form prescribed
by the IRS, certifying that such Lender Party is exempt from United States
federal withholding tax pursuant to Section 871(h) or Section 881(c) of the
Internal Revenue Code, together with an annual certificate in form and substance
satisfactory to such Subsidiary Guarantor or the Agent stating that such Lender
Party is not a "person" described in Section 871(h)(3) or 881(c)(3) of the
<PAGE>

Internal Revenue Code.  If the forms provided by a Lender Party at the time such
Lender Party first becomes a party to the Credit Agreement indicate a tax rate
with respect to Home Jurisdiction Withholding Tax in excess of zero, withholding
tax at such rate shall be considered excluded from Taxes unless and until such
Lender Party provides the appropriate form certifying that a lesser rate
applies, whereupon such withholding tax at such lesser rate only shall be
considered excluded from Taxes for periods governed by such form; provided,
                                                                  --------
however, that, if at the date of the Assignment and Acceptance pursuant to which
-------
a Lender Party becomes a party to the Credit Agreement, the Lender Party
assignor was entitled to payments under subsection (a) in respect of Home
Jurisdiction Withholding Tax with respect to interest paid at such date, then,
to such extent, the term Taxes shall include (in addition to withholding taxes
that may be imposed in the future or other amounts otherwise includable in
Taxes) Home Jurisdiction Withholding Tax, if any, applicable with respect to the
Lender Party assignee on such date.  If any form or document referred to in this
subsection (e) requires the disclosure of information not substantially similar
to the information necessary to compute the tax payable and information required
on the date hereof by IRS Form 1001 or 4224, and which a Lender Party reasonably
considers to be confidential, the Lender Party shall give notice thereof to each
Subsidiary Guarantor and shall not be obligated to include in such form or
document such confidential information.

     (f) For any period with respect to which a Lender Party has failed to
provide each Subsidiary Guarantor with the appropriate form described in
subsection (e) duly completed and executed (other than if such failure is due to
                                            ----- ----
a change in law occurring after the date on which a form originally was required
to be provided or if such form otherwise is not required under subsection (e)
above), such Lender Party shall not be entitled to indemnification under
subsection (a) or (c) of this Section 5 with respect to Taxes imposed by the
United States by reason of such failure; provided, however, that should a Lender
Party become subject to Taxes because of its failure to deliver a form required
hereunder, such Subsidiary Guarantor shall take such steps as such Lender Party
shall reasonably request at such Lender Party's sole expense to assist such
Lender Party to recover such Taxes.

     (g) Any Lender Party claiming additional amounts payable pursuant to this
Section 5 shall use reasonable efforts (consistent with its internal policy and
legal and regulatory restrictions) to file any certificate or document requested
by any Subsidiary Guarantor or to change the jurisdiction of its Applicable
Lending Office if the making of such filing or change would avoid the need for
or reduce the amount of any such additional amounts which may thereafter accrue
and would not, in the sole judgment of such Lender Party, be disadvantageous to
such Lender Party.

     (h) If any Lender Party receives a refund of any Taxes or Other Taxes paid
by such Subsidiary Guarantor pursuant to Section 5(a), Section 5(b), or Section
5(c), such Lender Party shall, within 30 days of such receipt, pay to such
Subsidiary Guarantor the amount so received, net of all out-of-pocket expenses
of such Lender Party with respect thereto, provided, however, that such Lender
                                           --------  -------
Party shall (i) be required to pay to such Subsidiary Guarantor only such
amounts as such Lender Party, in its sole discretion, determines is attributable
to Taxes or Other Taxes paid by such Subsidiary Guarantor pursuant to Section
5(a), Section 5(b) or Section 5(c), and (ii) have the sole discretion to
determine whether to contest the imposition of any Taxes or Other Taxes,
regardless of whether such Taxes or Other Taxes were correctly or legally
asserted.
<PAGE>

     SECTION 6.  Representations and Warranties.  Each Subsidiary Guarantor
                 ------------------------------
hereby represents and warrants as follows:

     (a) Such Subsidiary Guarantor (i) is a corporation duly organized, validly
existing and in good standing under the laws of the jurisdiction of its
incorporation, (ii) is duly qualified and in good standing as a foreign
corporation in each other jurisdiction in which it owns or leases property or in
which the conduct of its business requires it to so qualify or be licensed
except where the failure to so qualify or be licensed is not reasonably expected
to have a Material Adverse Effect and (iii) has all requisite corporate power
and authority (including, without limitation, all governmental licenses, permits
and other approvals) to own or lease and operate its properties and to carry on
its business as now conducted and as proposed to be conducted except to the
extent that the failure to do so is not reasonably expected to have a Material
Adverse Effect.  All of the outstanding capital stock of such Subsidiary
Guarantor has been validly issued, is fully paid and non-assessable and each
Subsidiary Guarantor is owned by a Loan Party, free and clear of all Liens,
except those created or permitted under the Loan Documents.

     (b) The execution, delivery and performance by such Subsidiary Guarantor of
this Subsidiary Guaranty are within such Subsidiary Guarantor's corporate
powers, have been duly authorized by all necessary corporate action, and do not
(i) contravene such Subsidiary Guarantor's charter or bylaws, (ii) violate any
law (including, without limitation, the Securities Exchange Act of 1934), rule,
regulation (including, without limitation, Regulation X of the Board of
Governors of the Federal Reserve System), order, writ, judgment, injunction,
decree, determination or award, (iii) conflict with or result in the breach of,
or constitute a default under, any loan agreement, contract, indenture,
mortgage, deed of trust, lease or other instrument binding on or affecting such
Subsidiary Guarantor, any of its Subsidiaries or any of its or their properties
the effect of which conflict, breach or default is reasonably likely to have a
Material Adverse Effect or (iv) except for the Liens created under the Loan
Documents, result in or require the creation or imposition of any Lien upon or
with respect to any of the properties of such Subsidiary Guarantor or any of its
Subsidiaries.  Neither such Subsidiary Guarantor nor any of its Subsidiaries is
in violation of any such law, rule, regulation, order, writ, judgment,
injunction, decree, determination or award or in breach of any such contract,
loan agreement, indenture, mortgage, deed of trust, lease or other instrument,
the violation or breach of which is reasonably expected to have a Material
Adverse Effect.

     (c) No authorization or approval or other action by, and no notice to or
filing with, any governmental authority or regulatory body or any other third
party is required for (i) the due execution, delivery, recordation, filing or
performance by such Subsidiary Guarantor of this Subsidiary Guaranty or any
other Loan Document to which such Subsidiary Guarantor is a party or (ii) the
exercise by the Agent or any Secured Party or any Hedge Bank of its rights under
this Subsidiary Guaranty or any other Loan Document to which such Subsidiary
Guarantor is a party.

     (d) There is no action, suit, investigation, litigation or proceeding
affecting such Subsidiary Guarantor, including any Environmental Action, pending
or threatened before any court, governmental agency or arbitrator that (i) is
reasonably expected to have a Material
<PAGE>

Adverse Effect or (ii) purports to affect the legality, validity or
enforceability of this Subsidiary Guaranty or any other Loan Document to which
such Subsidiary Guarantor is a party.

     (e) Each of this Subsidiary Guaranty and each other Loan Document to which
it is a party has been duly executed and delivered by such Subsidiary Guarantor.
Each of this Subsidiary Guaranty and each other Loan Document to which it is a
party is the legal, valid and binding obligation of such Subsidiary Guarantor,
enforceable against such Subsidiary Guarantor in accordance with its terms.

     (f) There are no conditions precedent to the effectiveness of this
Subsidiary Guaranty that have not been satisfied or waived.

     (g) Such Subsidiary Guarantor has, independently and without reliance upon
the Agent, any Lender Party or any Hedge Bank and based on such documents and
information as it has deemed appropriate, made its own credit analysis and
decision to enter into this Subsidiary Guaranty, and such Subsidiary Guarantor
has established adequate means of obtaining from each of the other Loan Parties
on a continuing basis information pertaining to, and is now, and on a continuing
basis will be, completely familiar with, the financial condition, operations,
properties and prospects of such other Loan Parties.

     SECTION 7.  Covenants.  Each Subsidiary Guarantor covenants and agrees
                 ---------
that, so long as any part of the Guaranteed Obligations constituting an Advance
or any other Guaranteed Obligation shall remain unpaid, any Letter of Credit or
Bankers' Acceptance shall be outstanding, any Lender Party shall have any
Commitment or any Hedge Bank shall have any obligation under any Bank Hedge
Agreement, such Subsidiary Guarantor will at all times perform or observe, and
will cause each of its Subsidiaries to perform or observe, all of the terms,
covenants and agreements that the Loan Documents state that the Borrower is to
cause such Subsidiary Guarantor or such Subsidiaries to perform or observe.

     SECTION 8.  Amendments, Etc.  (a)  No amendment or waiver of any provision
                 ---------------
of this Subsidiary Guaranty and no consent to any departure by any Subsidiary
Guarantor therefrom shall in any event be effective unless the same shall be in
writing and signed by the Agent and the Required Lenders, and then such waiver
or consent shall be effective only in the specific instance and for the specific
purpose for which given; provided, however, that any provision of this
                         --------  -------
Subsidiary Guaranty may be amended or waived in accordance with Section 8.01 of
the Credit Agreement.

     (b) Upon the execution and delivery by any Person of a guaranty supplement
in substantially the form of Exhibit A hereto (each a "Guaranty Supplement"),
                                                       -------------------
such Person shall be referred to as an "Additional Subsidiary Guarantor" and
                                        -------------------------------
shall be and become a Subsidiary Guarantor, and each reference in this Agreement
to "Subsidiary Guarantor" shall also mean and be a reference to such Additional
Subsidiary Guarantor.

     SECTION 9.  Notices, Etc .  All notices and other communications provided
                 ------------
for hereunder shall be in writing (including telegraphic or telecopy
communication) and mailed, telegraphed, telecopied or delivered to it, if to any
Subsidiary Guarantor, addressed to it at c/o D. George Harris & Associates,
Inc., 399 Park Avenue, 32nd Floor, New York, NY 10022,
<PAGE>

Attention: Treasurer, telecopier number (212) 207-6440, or, in the case of any
Additional Subsidiary Guarantor, at the address set forth below such Additional
Subsidiary Guarantor's signature on the applicable Guaranty Supplement, if to
the Agent or any Lender Party, at its address specified in the Credit Agreement,
if to any Hedge Bank, at its address specified in the Bank Hedge Agreement to
which it is a party, or as to any party at such other address as shall be
designated by such party in a written notice to each other party. All such
notices and other communications shall, when mailed, telegraphed, telecopied or
delivered, be effective when received by the addressee. Delivery by telecopier
of an executed counterpart of any supplement to or any amendment or waiver of
any provision of this Subsidiary Guaranty shall be effective as delivery of a
manually executed counterpart thereof.

     SECTION 10.  No Waiver; Remedies .  No failure on the part of the Agent or
                  -------------------
any other Secured Party to exercise, and no delay in exercising, any right
hereunder shall operate as a waiver thereof; nor shall any single or partial
exercise of any right hereunder preclude any other or further exercise thereof
or the exercise of any other right.  The remedies herein provided are cumulative
and not exclusive of any remedies provided by law.

     SECTION 11.  Right of Set-off .  Upon (a) the occurrence and during the
                  ----------------
continuance of any Event of Default and (b) either the making of the request or
the granting of the consent specified by Section 6.01 of the Credit Agreement to
authorize the Agent to declare the Advances due and payable pursuant to the
provisions of said Section 6.01 or the making of the demand specified by Section
6.02 of the Credit Agreement requiring the Borrower to pay amounts in respect of
Letters of Credit or the Canadian Borrower to pay amounts in respect of Bankers'
Acceptances, each Lender Party and each of its respective Affiliates is hereby
authorized at any time and from time to time, to the fullest extent permitted by
law, to set off and apply any and all deposits (general or special, time or
demand, provisional or final) at any time held and other indebtedness at any
time owing by such Lender Party or such Affiliate to or for the credit or the
account of any Subsidiary Guarantor against any and all of the Obligations of
such Subsidiary Guarantor now or hereafter existing under this Subsidiary
Guaranty, whether or not such Lender Party shall have made any demand under this
Subsidiary Guaranty and although such Obligations may be unmatured.  Each Lender
Party agrees promptly to notify such Subsidiary Guarantor after any such set-off
and application; provided, however, that the failure to give such notice shall
not affect the validity of such set-off and application.  The rights of each
Lender Party and its respective Affiliates under this Section are in addition to
other rights and remedies (including, without limitation, other rights of set-
off) that such Lender Party and its respective Affiliates may have.

     SECTION 12.  Continuing Subsidiary Guaranty; Assignments under the Credit
                  ------------------------------------------------------------
Agreement .  This Subsidiary Guaranty is a continuing guaranty and shall (a)
---------
remain in full force and effect until the later of the payment in full in cash
of the Guaranteed Obligations constituting an Advance or Drawing and all other
Guaranteed Obligations or amounts payable under this Subsidiary Guaranty and the
later of (i) and the Termination Date and (ii) the expiration or termination of
all Bank Hedge Agreements, (b) be binding upon each Subsidiary Guarantor, its
successors and assigns and (c) inure to the benefit of and be enforceable by the
Agent and the other Secured Parties and their successors, transferees and
assigns.  Without limiting the generality of the foregoing clause (c), any
Secured Party may assign or otherwise transfer all or any portion of its rights
and obligations under the Credit Agreement (including, without
<PAGE>

limitation, all or any portion of its Commitments, the Advances owing to it and
the Note or Notes held by it) to any other Person, and such other Person shall
thereupon become vested with all the benefits in respect thereof granted to such
Secured Party herein or otherwise, in each case as and to the extent provided in
Section 8.07 of the Credit Agreement. No Subsidiary Guarantor shall have the
right to assign its obligations hereunder or any interest herein without the
prior written consent of the Secured Parties.
<PAGE>

     SECTION 13.  Execution in Counterparts .  This Subsidiary Guaranty may be
                  -------------------------
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed shall be deemed to be an
original and all of which taken together shall constitute one and the same
agreement.  Delivery of an executed counterpart of a signature page to this
Subsidiary Guaranty by telecopier shall be effective as delivery of a manually
executed counterpart of this Subsidiary Guaranty.

     SECTION 14.  Governing Law; Jurisdiction; Waiver of Jury Trial, Etc.  (a)
                  ------------------------------------------------------
This Subsidiary Guaranty shall be governed by, and construed in accordance with,
the laws of the State of New York.

     (b) Each Subsidiary Guarantor hereby irrevocably and unconditionally
submits, for itself and its property, to the nonexclusive jurisdiction of any
New York State court or federal court of the United States of America sitting in
New York City, and any appellate court from any thereof, in any action or
proceeding arising out of or relating to this Subsidiary Guaranty or any of the
other Loan Documents to which it is or is to be a party, or for recognition or
enforcement of any judgment, and each Subsidiary Guarantor hereby irrevocably
and unconditionally agrees that all claims in respect of any such action or
proceeding may be heard and determined in any such New York State court or, to
the extent permitted by law, in such federal court.  Each Subsidiary Guarantor
agrees that a final judgment in any such action or proceeding shall be
conclusive and may be enforced in other jurisdictions by suit on the judgment or
in any other manner provided by law.  Nothing in this Subsidiary Guaranty shall
affect any right that any party may otherwise have to bring any action or
proceeding relating to this Subsidiary Guaranty or any of the other Loan
Documents to which it is or is to be a party in the courts of any jurisdiction.

     (c) Each Subsidiary Guarantor irrevocably and unconditionally waives, to
the fullest extent it may legally and effectively do so, any objection that it
may now or hereafter have to the laying of venue of any suit, action or
proceeding arising out of or relating to this Subsidiary Guaranty or any of the
other Loan Documents to which it is or is to be a party in any New York State or
federal court.  Each Subsidiary Guarantor hereby irrevocably waives, to the
fullest extent permitted by law, the defense of an inconvenient forum to the
maintenance of such action or proceeding in any such court.

     (d) Each Subsidiary Guarantor hereby irrevocably waives all right to trial
by jury in any action, proceeding or counterclaim (whether based on contract,
tort or otherwise) arising out of or relating to any of the Loan Documents, the
transactions contemplated thereby or the actions of the Agent or any other
Secured Party in the negotiation, administration, performance or enforcement
thereof.

     IN WITNESS WHEREOF, each Subsidiary Guarantor has caused this Subsidiary
Guaranty to be duly executed and delivered by its officer thereunto duly
authorized as of the date first above written.

                                       1
<PAGE>

                              PENNSYLVANIA GLASS SAND CORPORATION

                              By: /s/ Richard Nick
                                 --------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              THE FULTON LAND AND TIMBER COMPANY

                              By: /s/ Richard Nick
                                 --------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              OTTAWA SILICA COMPANY

                              By: /s/ John A. Ulizio
                                 --------------------------------------
                                 Name:
                                 Title:

                              GEORGE F. PETTINOS, INC.

                              By: /s/ Richard Nick
                                 --------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              ELLEN JAY, INC.

                              By: /s/ Richard Nick
                                 --------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              U.S. SILICA COMPANY (a/k/a U.S. Silica Company,
                              Inc.)

                              By: /s/ Richard Nick
                                 --------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                                       1
<PAGE>

                              BETTER MATERIALS CORPORATION

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              BMC TRUCKING, INC.

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              BUCKS COUNTY CRUSHED STONE COMPANY

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              CHIPPEWA FARMS CORPORATION

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              SHORE STONE COMPANY, INC.

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              COMMERCIAL STONE CO., INC.

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                                       1
<PAGE>

                              STONE MATERIALS COMPANY, LLC

                              By: Better Minerals & Aggregates Company, as
                              Manager

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                              COMMERCIAL AGGREGATES TRANSPORTATION AND SALES,
                              LLC

                              By: Stone Materials Company, LLC, as Manager

                              By: /s/ Richard Nick
                                 ------------------------------------
                                 Name: Richard Nick
                                 Title:   Vice President

                                       1
<PAGE>

                                   EXHIBIT A
                                       to
                              Subsidiary Guaranty


                     FORM OF SUBSIDIARY GUARANTY SUPPLEMENT



Banque Nationale de Paris,
  as Agent
499 Park Avenue
New York, New York  10022
Attention:  Structured Finance Group


               Subsidiary Guaranty dated as of September 30, 1999
                   made by ______________________ in favor of
                    the Secured Parties referred to therein
                    ---------------------------------------


Ladies and Gentlemen:

               Reference is made to the above-captioned Subsidiary Guaranty (as
amended, supplemented or otherwise modified, the "Subsidiary Guaranty").
                                                  -------------------
Unless otherwise defined herein, terms defined in the Subsidiary Guaranty and in
the Credit Agreement referred to therein are used herein as therein defined.

               The undersigned affirms that it may receive a portion of the
proceeds of the Advances under the Credit Agreement and will derive substantial
direct and indirect benefit from the transactions contemplated by the Credit
Agreement, in consideration for the execution and delivery of this Subsidiary
Guaranty Supplement.

               The undersigned hereby agrees, as of the date first above
written, to become a Subsidiary Guarantor under the Subsidiary Guaranty as if
it were an original party thereto and agrees that each reference in the
Subsidiary Guaranty to a "Subsidiary Guarantor" shall also mean and be a
reference to the undersigned.

               The undersigned hereby unconditionally and irrevocably guarantees
the punctual payment when due, whether at stated maturity, by acceleration or
otherwise, of all Obligations of each other Loan Party now or hereafter existing
under the Loan Documents to the extent set forth therein.

                                       1
<PAGE>

               The undersigned hereby makes each representation and warranty set
forth in Section 6 of the Subsidiary Guaranty to the same extent as each other
Subsidiary Guarantor and hereby agrees to be bound as a Subsidiary Guarantor by
all of the terms and provisions of the Subsidiary Guaranty to the same extent as
all other Subsidiary Guarantors.

               This letter shall be governed by and construed in accordance with
the laws of the State of New York.

                              Very truly yours,

                              [NAME OF ADDITIONAL SUBSIDIARY
                              GUARANTOR]

                              By _______________________________________
                                 Name:
                                 Title:
                                 Address:

                                       1
<PAGE>

                                                                EXHIBIT I TO THE
                                                                CREDIT AGREEMENT



                                    FORM OF
                              SUBSIDIARY GUARANTY

                        Dated as of September 30, 1999

                                     From

               THE PERSONS LISTED ON THE SIGNATURE PAGES HEREOF

                           as Subsidiary Guarantors

                                  in favor of

                      THE SECURED PARTIES REFERRED TO IN
                    THE CREDIT AGREEMENT REFERRED TO HEREIN
<PAGE>

                                 EXECUTION COPY


                              SUBSIDIARY GUARANTY

                         Dated as of September 30, 1999

                                      From

                THE PERSONS LISTED ON THE SIGNATURE PAGES HEREOF

                            as Subsidiary Guarantors
                            -- ---------- ----------

                                  in favor of

                       THE SECURED PARTIES REFERRED TO IN
                    THE CREDIT AGREEMENT REFERRED TO HEREIN
<PAGE>

                               TABLE OF CONTENTS
                               -----------------

<TABLE>
<CAPTION>
Section                                                                    Page
<S>                                                                        <C>
SECTION 1.   SUBSIDIARY GUARANTY; LIMITATION OF LIABILITY                     1
SECTION 2.   SUBSIDIARY GUARANTY ABSOLUTE
SECTION 3.   WAIVERS AND ACKNOWLEDGMENTS
SECTION 4.   SUBROGATION
SECTION 5.   PAYMENTS FREE AND CLEAR OF TAXES, ETC
SECTION 6.   REPRESENTATIONS AND WARRANTIES
SECTION 7.   COVENANTS
SECTION 8.   AMENDMENTS, ETC
SECTION 9.   NOTICES, ETC
SECTION 10.  NO WAIVER; REMEDIES
SECTION 11.  RIGHT OF SET-OFF
SECTION 12.  CONTINUING SUBSIDIARY GUARANTY; ASSIGNMENTS UNDER
             THE CREDIT AGREEMENT
SECTION 13.  EXECUTION IN COUNTERPARTS
</TABLE>
<PAGE>

<TABLE>
<S>                                                                          <C>
SECTION 14.  GOVERNING LAW; JURISDICTION; WAIVER OF JURY TRIAL, ETC          11
</TABLE>