Bentonite is a rock, which is named after the Benton Formation in the Fort Benton slates of Wyoming in the United States. Bentonite is a mixture of different clay minerals, which contains montmorillonite (our Bentonite products have a min. content of 65% montmorillonite). Latter explains the intensive water absorption and swelling capability of Bentonite. Further accompanying minerals are quartz, mica, feldspar, pyrite or calcite. Bentonite is made from the weathering of vulcanic ash.