Mineral Species: Jarosite

Chemical Formula: KFe3(SO4)2(OH)6

Chemical Name: Potassium Iron Sulfate Hydroxide

Mineral Class: Sulphate

Mineral Notes: Jarosite is a rare mineral closely related to the mineral Natrojarosite. Both are isostructural which means that they have the same crystal structure but different chemistries. In this case, Jarosite contains potassium instead of Natrojarosite's sodium. In addition, both minerals are isostructural with Alunite, with a formula of KAl3(SO4)2(OH)6, who lends its name to the Alunite Group of which all three minerals belong. The symmetry of Jarosite is the same as the members of the Tourmaline Group. Crystals of Jarosite however do not form prismatic crystals like those of the typical tourmaline mineral. Jarosite's crystals are more flattened and resemble nearly cubic rhombohedrons. These are actually a combination of two trigonal pyramids.  

Description: Large, lustrous crystals of red-brown Jarosite nestling a matrix cavity. Others are scattered over the surface of the specimen. A particularly attractive feature is crystalline mass of white Clacite to one side of the cavity which provides a very striking contrast.

Location: Barranco Jaroso Mine, Aquilas, Sierra Almagrera, Murcia, Spain.