Annite
Annite
Phyllosilicate mineral in the mica family
Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe32+AlSi3O10(OH)2.[8] Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite.[9] Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines.[6] There are contact twins with composition surface {001} and twin axis {310}.[10]
Annite was first described in 1868 for the first noted occurrence in Cape Ann, Rockport, Essex County, Massachusetts, US.[7] It also occurs on Pikes Peak, El Paso County, Colorado.[8] It occurs in igneous and metamorphic rocks that are deficient in magnesium and is associated with fluorite and zircon in the type locality.[8]