sedimentary

Bentonite Clay

Montmorillonite ((Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·nH2O)

AI-generated identification · may be incorrect

Hardness: 1-2 (Mohs scale), Color: Cream, off-white, or pale yellow, Luster: Dull/Earthy, Crystal Structure: Monoclinic (microscopic), Cleavage: Perfect basal (microscopic), Specific Gravity: 2.2-2.7

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 1-2 (Mohs scale), Color: Cream, off-white, or pale yellow, Luster: Dull/Earthy, Crystal Structure: Monoclinic (microscopic), Cleavage: Perfect basal (microscopic), Specific Gravity: 2.2-2.7

Formation & geological history

Formed through the chemical weathering of volcanic ash in the presence of water (diagenesis), typically in marine or lacustrine environments during the Mesozoic or Cenozoic eras.

Uses & applications

Used as a drilling mud in the oil industry, as a binder in iron ore pelletizing, in foundry sand, in cosmetics such as face masks, and as a sealant for ponds or landfills due to its swelling properties.

Geological facts

Bentonite can expand up to 15-20 times its original dry volume when saturated with water, making it an incredible natural sealant.

Field identification & locations

Identify in the field by its soapy or waxy feel when wet and its tendency to stick to the tongue. Commonly found in the Fort Benton Formation in Wyoming, USA.