Mineral description : Biotite

Biotite book from Umeå.

Mineral class Silicates : Phyllosilicates : Mica group.
Chemical formula K(Mg,Fe)3(OH,F)2(AlSi3O10)
Crystal system Monoclinic.
Habitus Rarely as small hexagonal crystals. Often as books of mica.
Cleavage Basally perfect.
Hardness 2.5-3
Density 2.8-3.2
Color Black, dark brown, reddish brown, green and rarely white.
Streak Colorless.
Luster Vitreous.
Description  
Occurance Common in both igneous and metamorphic rocks.
Associates  
Notes Soluble in concentrated sulfuric acid.
Locations A very common mineral with big crystal books at many places, for instance :
  • Kolsva, Västmanland.
  • Derome, Halland. Up to 1m crystal books.
  • Brännland quarry, Umeå, Västerbotten. As up to 40cm crystal books in a pegmatite.

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If you have some questions, suggestions or comments you are welcome to write me a line or two.


axelsson@acc.umu.se
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Last changed : 1998-08-26