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I'm hoping I can claim short term memory loss on this - after close scrutiny on the bag it says arcillite.
Arcillite - calcined, montmorillonite clay.
Montmorillonite - one of the major components of bentonite and fuller's earth. Hydrous aluminum silicate with a considerable capacity for exchanging part of the aluminum for Mg and bases. High natural adsorptive power. Good CEC.