Category Sulfate minerals Strunz classification 7.CB.85 Space group P21/c | Formula
(repeating unit) FeAl2(SO4)4·22H2O Crystal system Monoclinic | |
 | ||
Crystal class Prismatic (2m)
(same H-M symbol) | ||
Halotrichite, also known as feather alum, is a highly hydrated sulfate of aluminium and iron. Its chemical formula is FeAl2(SO4)4·22H2O. It forms fibrous monoclinic crystals. The crystals are water-soluble.
It is formed by the weathering and decomposition of pyrite commonly near or in volcanic vents. The locations of natural occurrences include: the Atacama Desert, Chile; Dresden in Saxony, Germany; San Juan County, Utah; Iceland and Mont Saint-Hilaire, Canada.
The name is from Latin: halotrichum for salt hair which accurately describes the precipitate/evaporite mineral.
References
Halotrichite Wikipedia(Text) CC BY-SA