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.

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.

This article about a specific sulfate mineral is a stub.