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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