Annite
Chemical compound
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Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe₃²⁺AlSi₃O₁₀(OH)₂. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Annite is monoclinic and... Wikipedia
Color: Brown to black
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal system: Monoclinic
Formula (repeating unit): KFe32+AlSi3O10(OH,F)2
Fracture: Uneven
Luster: Submetallic to vitreous; pearly on cleavage surfaces
Optical properties: Biaxial (−)