Annite

Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe₃AlSi₃O₁₀(OH,F)₂. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines. There are contact twins with composition surface {001} and twin axis {310}.