sedimentary
Bentonite Clay
Al2O3·4SiO2·H2O (Hydrous aluminum silicate)
Hardness: 1-2 (Mohs); Color: Cream, tan, or yellowish-grey; Luster: Dull/Earthy; Texture: Fine-grained, waxy when moist; Structure: Monoclinic crystal system.
- Hardness
- 1-2 (Mohs)
- Color
- Cream, tan, or yellowish-grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 1-2 (Mohs); Color: Cream, tan, or yellowish-grey; Luster: Dull/Earthy; Texture: Fine-grained, waxy when moist; Structure: Monoclinic crystal system.
Formation & geological history
Formed through the chemical alteration of volcanic ash in the presence of water (typically in marine environments). Its formation can range from the Cretaceous to more recent periods.
Uses & applications
Used in drilling mud, as a binding agent in iron ore pelletizing, in facial masks/cosmetics, for groundwater sealing, and as a clarifier in wine and oil production.
Geological facts
It has the remarkable ability to expand to several times its original dry volume when saturated with water, forming a gelatinous mass.
Field identification & locations
Identify by its soapy or waxy feel and its tendency to swell and become sticky when wet. Found commonly in layers within sedimentary basins, particularly in the western United States (Wyoming).
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