Class : Sulfates, chromates, molybdates
    Subclass : Anhydrous sulfates
    Crystal system : Trigonal
    Chemistry : KFe₃(SO₄)₂(OH)₆
    Rarity : Common

Jarosite is a secondary mineral very common in the oxidation zone of deposits containing iron, in an arid climate. With other iron sulfates (copiapite, voltaite, römerite, amarantite, botryogen, fibroferrite, etc...), it belongs to a classic mineralogical procession resulting like it from precipitation from concentrated acid solutions (natural sulfuric acid from of the reaction of surface water with iron sulfides). By changing environmental conditions (temperature, pH, redox potential, etc...) these sulfates are easily hydrolyzed into ferric hydroxides (goethite and limonite). Jarosite, sulfates, and iron hydroxides are particularly common in gossans of pyrite clusters and pyrite-rich hydrothermal veins. It is also found in certain industrial slags. Its name derives from its place of discovery : Barranco Jaroso (Spain). Jarosite occurs quite often in encrustations, in compact granular, concretionary or earthy masses, rarely in flattened and very small rhombohedral crystals (3 mm maximum). It is ocher-yellow to dark brown in color, rarely gray-yellow.

Main photo : Jarosite from Grand Central Mine, Arizona, USA © Stephan Wolfsried

No twin known for this mineral species.

No fakes recorded for this mineral species.