sedimentary
Bentonite Clay
Montmorillonite (Al2H2O12Si4)
Soft, earthy, powdery texture. Color ranges from light gray to greenish-yellow. Hardness 1-2 (Mohs scale), dull luster, monoclinic crystal system (microscopic).
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Physical properties
Soft, earthy, powdery texture. Color ranges from light gray to greenish-yellow. Hardness 1-2 (Mohs scale), dull luster, monoclinic crystal system (microscopic).
Formation & geological history
Forms primarily from the chemical weathering and alteration of volcanic ash in the presence of water (usually in marine environments). Deposits can range from Cretaceous to Tertiary periods.
Uses & applications
Used in drilling mud, as a binder in foundry sand, in iron ore pelletizing, as a clarifying agent for liquids, and in beauty products/face masks.
Geological facts
It is known as the 'clay of a thousand uses' and has the unique property of swelling massively (up to 15 times its dry volume) when exposed to water.
Field identification & locations
Identified by its soapy or waxy feel when wet and its tendency to stick to the tongue. Commonly found in the Western United States (Wyoming) and volcanic regions worldwide.
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