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Mineralpedia Details for Annite

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Annite

Annite

Formula
KFe2+3(Si3Al)O10(OH)2 
Crystal System
Monoclinic 
Cleavage
Perfect, None, None 
Luster
Sub Metallic 
Color
reddish brown, black 
Streak
brownish white 
Class
Monoclinic - Prismatic 
Hardness
2.5-3 
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Mindat
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Annite from Poudrette quarry, Mont Saint-Hilaire, Montérégie, Québec, Canada

Annite
            from Poudrette quarry, Mont Saint-Hilaire, Montérégie, Québec, Canada

Dark black crystals to 1.7cm, which would usually be called biotite. Most "biotites" are in fact Annite. The crystal on the second photo is pseudohexagonal.

Annite is the iron rich, OH end member, of the Biotite- Phlogopite series. Common in schists, worldwide, occuring up to 3meters (!!) as crystals in granites of Cape Ann near Rockport, Mass. USA, and crystals up to 15cm from MSH (Bernard & Hrysl). Sometimes forming pseudohexagonal outlines, and foliated masses, in Mg poor igneous and metamorphc rocks.

Phyllosilicate Mica group member. Ordinary (True or Common) Mica - Trioctahderal. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

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