Bentonite clay
Image: Helgi (CC BY-SA 3.0)
Mineral NameBentonite clay
Chemical Formula(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O
Mohs Hardness1
Crystal Systemmonoclinic
Lusterdull
Streak Colorwhite to light brown
CleavageNot applicable in bulk clay form
Fractureearthy
Specific Gravity2
Colorslight brown, tan, beige
Transparencyopaque
Type LocalityLviv (Lemberg), Ukraine
Mineral GroupPhyllosilicates
Usesdrilling mud, adsorbent, cat litter, cosmetics, pharmaceuticals, binder
Associated Mineralsmontmorillonite, kaolinite, illite, quartz, feldspar
Raritycommon
Description
The image displays dried bentonite clay, light brown in color, which has extensively cracked into numerous polygonal fragments, revealing a lighter surface beneath.
Geological Context
Bentonite is an absorbent clay rock primarily composed of montmorillonite, formed from the alteration of volcanic ash, typically tuff, in the presence of water in marine or freshwater environments.
