Mineral description : Montmorillonite

Montmorillonite from Varuträsk.

Mineral class Silicates : Phyllosilicates : Kaolinite - Montmorillonite group.
Chemical formula (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2.nH2O
Crystal system Orthorombic.
Habitus Earthy.
Hardness 1
Density 1.7-2.7
Color White to gray, also as pinkish white, reddish white or brownish white.
Streak White
Luster Vitreous to resinous, translucent to transparent.
Occurance As a weathering product from silica poor rocks.
Locations A rare mineral in Sweden.
  • Varuträsk, Västerbotten. As pink aggregates and fracture fillings. created by weathering of petalite.
  • Ultevis, Jokkmokk, Lappland. On weathered scapolite.
  • Alnön, Sundsvall, Medelpad.
  • Kinekulle, Västergötland. In weathered bentonite (volcanic ash).
  • Boda, Dalarna. In weathered bentonite (volcanic ash).

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Last changed : 1998-09-17