Jarosite

  Jarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe³⁺₃(OH)₆(SO₄)₂. This mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct during the purification and refining of Zinc and is also commonly associated with AMD (acid mine drainage) environments.

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Physical Properties

Jarosite is hexagonal and brittle, with basal cleavage, a hardness of 2.5-3.5, and a specific gravity of 3.15-3.26. It is translucent to opaque with a vitreous to dull lustre, and is coloured dark yellow to yellowish-brown. It can sometimes be confused with limonite or goethite with which it commonly occurs in the gossan (oxidized cap over an ore body). Jarosite is an iron analogue of the potassium aluminium sulfate, alunite.

History

Jarosite was first described in 1852 by August Breithaupt in the Barranco del Jaroso in the Sierra Almagrera (near Los Lobos, Cuevas del Almanzora, Almería, Spain).

In 2004 Jarosite was detected by the rover's Mössbauer spectrometer on Mars by the MER-B rover, which has been interpreted as strong evidence that Mars once possessed large amounts of liquid water.

Use in materials science

Jarosite is also a more generic term denoting an extensive family of compounds of the form AM₃(OH)₆(SO₄)₂, where A⁺ = Na, K, Rb, NH₄, H₃O, Ag, Tl and M³⁺ = Fe, Cr, V. In condensed matter physics and materials science they are renowned for containing layers with kagome lattice structure, relating to geometrically frustrated magnets^{[1], [2]}.

References

• Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, 560–562
• Mindat
• Webmineral data
• Mineral Data PDF
• Cornell University (2004) How an obscure mineral provided a vital clue to Martian water