These might help a little.

Attapulgite clay
A fibrous claylike material, essentially ((OH 2 ) 4 Mg 5 Si 8 O 20 (OH) 2 -- 4H 2 O), rich in magnesium, and used as a filling material in papermaking, usually in coatings for reproduction papers. The clay is also called "fuller's earth," from its ability to remove dirt and grease from wool, a process called "fulling."

Mining Association of South Carolina