- Schwertmannite
Schwertmannite is an iron-oxyhydroxysulfate
mineral with an ideal chemical formula of Iron8Oxygen8(Hydroxide)6(Sulfate)·nH2O or Fe3+16O16(OH,SO4)12-13·10-12H2O. [http://www.mindat.org/min-7281.html Mindat] It is an opaquetetragonal mineral typically occurring as brownish yellow encrustations. It has aMohs hardness of 2.5 - 3.5 and aspecific gravity of 3.77 - 3.99. [http://webmineral.com/data/Schwertmannite.shtml Webmineral]It was first described for an occurrence in
Finland in 1994 and named for Udo Schwertmann (1922 - ) soil scientist, Technical University of Munich,Munich, Germany . [http://rruff.geo.arizona.edu/doclib/hom/schwertmannite.pdf Mineral Handbook]Schwertmannite (with a distinct "pin cushion" morphology) commonly forms in iron-rich, acid sulfate waters in the pH-range of 2 - 4.. The mineral was first recognised officially as a new mineral from a natural acid-sulfate spring occurrence at Pyhasalmi, Finland. [Bigham, JM, Carlson, L, Murad, E (1994) Schwertmannite, a new iron oxyhydroxysulfate from Pyhasalmi, Finland, and other localities. "Mineral Mag" 58, 641-664] However, it is more commonly reported as an orange precipitate in streams and lakes affected by acid-mine drainage. [Bigham, JM, Schwertmann, U, Carlson, L, Murad, E (1996) Schwertmannite and the chemical modeling of iron in acid sulfate waters. "Geochimica et Cosmochimica Acta" 54, 2743-2758.] Schwertmannite is also known to be central to iron-sulfur geochemistry in acid-sulfate soils associated with coastal lowlands. [Burton, ED, Bush, RT, Sullivan, LA (2007) Reductive transformation of iron and sulfur in schwertmannite-rich accumulations associated with acidified coastal lowlands. "Geochimica et Cosmochimica Acta" 71, 4456-4473]
References
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