sedimentary

Bentonite Clay

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

AI-generated identification · may be incorrect

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

Identified July 17, 2026More sedimentary →

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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.