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Halotrichite
Chemical Formula	FeAl2(SO4)4·22H2O.
Species	Sulfates
Crystal System	Monoclinic
Mohs Scale	1-2
Specific Gravity	1.89
Color	colourless to white, yellowish, greenish
Luster	vitreous
Diaphaneity	transparent, translucent
Cleavage	poor/indistinct
Fracture	conchoidal

Halotrichite, also known as feather alum, is a highly hydrated sulfate of aluminium and iron. It is formed by the weathering and decomposition of pyrite commonly near or in volcanic vents. Its chemical formula is FeAl₂(SO₄)₄·22H₂O. It forms fibrous monoclinic crystals. The crystals are water soluble. Occurrences include the Atacama Desert, Chile, Dresden, Saxony, Germany, San Juan County, Utah, and Mont Saint-Hilaire, Canada.

The name is from Latin: halotrichum for salt hair.