ADDITIONAL GUARANTOR SUPPLEMENT

                                                                    EXHIBIT 10.1

                                                                  CONFORMED COPY

                         ADDITIONAL GUARANTOR SUPPLEMENT

                                                                    March 8, 2007

Harris N.A., as Administrative Agent for the Lenders named in the Credit
Agreement dated as of November 10, 2005, among AMCOL International Corporation,
certain Subsidiary Borrowers, the Guarantors from time to time party thereto,
the Lenders from time to time party thereto, and the Administrative Agent (the
"Credit Agreement")

Ladies and Gentlemen:

         Reference is made to the Credit Agreement described above. Terms not
defined herein which are defined in the Credit Agreement shall have for the
purposes hereof the meaning provided therein.

         The undersigned, CETCO Oilfield Services Company, a Delaware
corporation hereby elects to be a "Guarantor" for all purposes of the Credit
Agreement, effective from the date hereof. The undersigned confir