Geology Home Page
Roger Weller, geology instructor
Chemical Group: silicate- a clay mineral
Chemical Formula: (Mg,Ca)O.Al2O3.5SiO2.nH2O
Color: gray, greenish gray, white, yellow, yellow green, pink, brown Streak: white
Luster: greasy or dull
Hardness: 2 to
Specific Gravity: 2.0 to 2.7
Crystal Forms: Monoclinic system
A clay mineral; crystals are exceedingly tiny.
Mineral Associations: Bentonite is a rock made of montmorillonite
Identifying Characteristics: soapy feeling and expanding when wet
Uses: drilling mud
Occurrences: Wyoming, Texas, and Mississippi
Toxicity: when-swallowed- low when inhaled- low to moderate
Additional Information: Montmorillonite is responsible for expanding soils which affect buildings.