Annite is a
phyllosilicate mineral in the
mica family. It has a chemical formula of KFe
32+AlSi
3O
10(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}.