Montmorillonite identification and geology

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner

GeoMiner

Last updated

2026-03-30T14:36:48.964331+00:00

Review status

Published; not independently peer-reviewed

• IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
• Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.

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Common questions

What is Montmorillonite?

Swelling clay mineral of the smectite group. Absorbs water and expands dramatically, used in drilling muds and cat litter.

How can you identify Montmorillonite?

Compare several properties rather than relying on colour alone. This entry records colour: White, gray, yellowish, greenish; lustre: Earthy to dull; streak: White; Mohs hardness: 1-2; cleavage: Perfect basal; crystal system: Monoclinic; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.

How does Montmorillonite form?

Forms from weathering and hydrothermal alteration of volcanic ash and mafic igneous rocks.

Where is Montmorillonite commonly found?

Worldwide; Montmorillon France , Wyoming bentonite , India.

What is Montmorillonite commonly confused with?

Montmorillonite may be confused with Kaolinite, Illite, Vermiculite. Compare multiple diagnostic properties because colour and surface appearance can overlap.