From Open Energy Information

A hydrated aluminum, potassium, sulfate mineral often found around fumaroles
Other definitions:Wikipedia Reegle

Alunite crystals from the Zemplén Mtns, Hungary. Photo by Harold Moritz 2012.

Alunite is a potassium sulfate mineral that forms in acid-vapor dominated hydrothermal systems. It is commonly encountered as an alteration mineral in high sulfidation epithermal gold deposits formed from acid-sulfate solutions and in areas with past fumarolic activity.


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