Jarosite
Image: Andrew Silver (Public domain)
Mineral NameJarosite
Chemical FormulaKFe3(SO4)2(OH)6
Mohs Hardness2.5
Crystal Systemtrigonal
Lustervitreous
Streak Colorpale yellow to brownish-yellow
Cleavagedistinct on {0001}, but rarely observed due to fine grain size
Fractureuneven to splintery
Specific Gravity3.16
Colorsyellow, yellowish-brown, brown, reddish-brown
Transparencytranslucent to opaque
Type LocalityCommon in oxidized sulfide deposits worldwide, including various acid mine drainage sites.
Mineral GroupSulfates
Usesindicator mineral for acid sulfate soils and acid mine drainage, minor source of iron, collector's specimen
Associated Mineralspyrite, goethite, limonite, other iron oxides and hydroxides
Raritycommon
Description
This specimen displays jarosite as a yellowish-brown, earthy to finely crystalline mass, exhibiting a dull to somewhat vitreous luster.
Geological Context
Jarosite is a secondary mineral that forms in the oxidized zones of sulfide ore deposits, particularly in acid mine drainage environments, where iron sulfides like pyrite are weathered in the presence of potassium and sulfate.
