Jarosite
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Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe 3 (SO 4 ) 2 (OH) 6 . This sulfate 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 acid mine drainage and acid sulfate soil environments.
Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe 3 (SO 4 ) 2 (OH) 6 . This sulfate 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 acid mine drainage and acid sulfate soil environments.
Physical properties
Jarosite has a trigonal crystal structure and is 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 luster, and is colored 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. In the jarosite-natrojarosite series Na substitutes for K to at least Na/K = 1:2.4 but the pure sodium end member NaFe 3 (SO 4 ) 2 (OH) 6 is not known in nature. Minerals with Na > K are known as natrojarosite. End member formation (jarosite and natrojarosite) is favoured by a low temperature environment, less than 100 °C, and is illustrated by the oscillatory zoning of jarosite and natrojarosite found in samples from the Apex Mine, Arizona, and Gold Hill, Utah. This indicates that there is a wide miscibility gap between the two end members, and it is doubtful whether a complete series exists between jarosite and natrojarosite. In hydroniumjarosite the hydronium ion H 3 O + can also substitute for K + , with increased hydronium ion content causing a marked decrease in the lattice parameter c, although there is little change in a. Hydroniumjarosite will only form from alkali-deficient solutions, as alkali-rich jarosite forms preferentially. Divalent cations may also substitute for the monovalent cation K + in the A site. Charge balance may be achieved in three ways. Firstly by replacing two monovalent cations by one divalent cation, and leaving an A site vacancy, as in plumbogummite, Pb 2+ Al 3 (PO 4 ) 2 (OH) 5 .H 2 O, which is a member of the crandallite subgroup. Secondly by incorporating divalent ions in the B sites, as in osarizawaite, Pb 2+ Cu 2+ Al 2 (SO 4 ) 2 (OH) 6 , alunite subgroup, and beaverite, Pb 2+ Cu 2+ (Fe 3+ ,Al) 2 (SO 4 ) 2 (OH) 6 , jarosite subgroup. Thirdly by replacing divalent anions with trivalent anions, as in beudantite, PbFe 3+ 3 (AsO 4 ) 3− (SO 4 )(OH) 6 , beudantite subgroup. Jarosite is also a more generic term denoting an extensive family of compounds of the form AM 3 (OH) 6 (SO 4 ) 2 , where A + = Na, K, Rb, NH 4 , H 3 O, Ag, Tl and M 3+ = 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.
See also
Alunite Iron(III) sulfate Spirit Mars rover final embedding event
External links
Further information about the Jaros Hydrothermal system
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