sedimentary
Bentonite Clay
Montmorillonite silicate ((Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·nH2O)
Hardness: 1-2 (Mohs); Color: Pale buff, tan, or greenish-gray; Luster: Dull or earthy; Crystal structure: Monoclinic; Cleavage: Perfect; Texture: Soapy or greasy when wet.
- Hardness
- 1-2 (Mohs)
- Color
- Pale buff, tan, or greenish-gray
- Luster
- Dull or earthy
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Physical properties
Hardness: 1-2 (Mohs); Color: Pale buff, tan, or greenish-gray; Luster: Dull or earthy; Crystal structure: Monoclinic; Cleavage: Perfect; Texture: Soapy or greasy when wet.
Formation & geological history
Formed primarily from the chemical weathering and alteration of volcanic ash in marine or alkaline lake environments. Common in Cretaceous and tertiary geological formations.
Uses & applications
Used as drilling mud in oil and gas wells, as a binder in foundry sand, in cat litter, as a clarifying agent for wines, and in cosmetics and skincare masks.
Geological facts
Bentonite can expand up to 15 times its original dry volume when saturated with water, making it an excellent sealant for ponds and landfill liners.
Field identification & locations
Identified by its distinctive swelling property and slippery, soapy feel when moistened. Commonly found in the western United States (Wyoming) and parts of the Middle East.
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