A sample of Halotrichite

Halotrichite from California

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.

[edit] References

• Webmineral
• Saint-Hilaire
• Mineral Atlas