What is Montmorillonite?
Montmorillonite turns microscopic layer chemistry into a visible material property: it absorbs water, expands and changes consistency. A labelled bentonite or clay specimen connects mineral structure with soils, drilling and environmental geology.
Mineralogy and crystal structure
Reference formula: Na0.3(Al,Mg)2Si4O10(OH)2·8H2O. Montmorillonite is a swelling smectite clay with variable interlayer cations and water. No single ideal composition describes every natural sample; the displayed structure is a representative layered model, not a claim that all montmorillonite has identical occupancy or hydration. Montmorillonite is classified with silicates and has a monoclinic crystal system. Typical hardness is 1–2 on the Mohs scale and specific gravity is approximately 2.0–2.7.
Colour, lustre and habit
Typical colours include white, grey, cream, green, pink. The usual earthy, massive, micaceous habit and dull, earthy, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Montmorillonite forms in or is associated with alteration of volcanic ash and glass, bentonite beds, soils and hydrothermal environments. Important documented localities include the United States, France, Italy, Japan, Turkey and Greece.
The swelling clay behind bentonite
Montmorillonite turns microscopic layer chemistry into a visible material property: it absorbs water, expands and changes consistency. A labelled bentonite or clay specimen connects mineral structure with soils, drilling and environmental geology.
Collecting and care
Keep dry and avoid inhaling dust; humidity changes can expand the material and alter its texture.
