Montmorillonite
Mineral (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2·nH2O
Also called Smectite and Bentonite
Take care.
- Damaged by water: Keep it dry: don't wash it, and keep it out of damp places.
About it
A clay that swells and turns slippery when wet; the main mineral of bentonite, mined in Wyoming. Pink massive material was first described from Montmorillon, France.
- Type
- Mineral
- Group
- Silicate (phyllosilicate), smectite group
- Formula
- (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2·nH2O
- Hardness (Mohs)
- 1–2
- Specific gravity
- 2–3
- Streak
- white
- Lustre
- dull, earthy
- Crystal system
- Monoclinic
- Colours
- white, pink, buff, yellow, green, red
- Transparency
- opaque
- Cleavage and fracture
- perfect in one direction (microscopic)
Typical values: real specimens vary. For more, see mindat.org.