Halotrichite
（重定向自Feather Alum）
![](/Images/godic/202501/12/Mineraly.sk_-_halotrichit5920.jpg")
![Halotrichite from California](/Images/godic/202501/12/Halotrichite_Hydrous_iron_aluminum_sulfate_Corral,_California_30095920.jpg")
![Halotrichite from the abandoned Golden Queen mine on Soledad Mountain south of Mojave, California](/Images/godic/202501/12/Halotrichite-1796345920.jpg")
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.