Schwertmannite

Schwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of Fe8O8(OH)6(SO4)·nH2O or Fe3+16O16(OH,SO4)12-13·10-12H2O.[1] It is an opaque tetragonal mineral typically occurring as brownish yellow encrustations. It has a Mohs hardness of 2.5 - 3.5 and a specific gravity of 3.77 - 3.99.[2]

Schwertmannite
Schwertmannite
General
CategorySulfate minerals
Formula
(repeating unit)		Fe8O8(OH)6(SO4)·nH2O
Strunz classification7.DE.15
Crystal systemTetragonal
Dipyramidal class
Space groupTetragonal
H-M symbol: (4/m)
Space group: P4/m
Identification
Colorbrownish yellow
Lusterearthy
Streakyellow
Diaphaneityopaque
References[1][2]

It was first described for an occurrence in Finland in 1994 and named for Udo Schwertmann (born 1927) soil scientist, Technical University of Munich, Munich, Germany.[3]

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 Pyhäsalmi, Finland.[4] However, it is more commonly reported as an orange precipitate in streams and lakes affected by acid mine drainage.[5] Schwertmannite is also known to be central to iron-sulfur geochemistry in acid sulfate soils associated with coastal lowlands.[6]

References
  1. Mindat
  2. http://webmineral.com/data/Schwertmannite.shtml Webmineral
  3. http://rruff.geo.arizona.edu/doclib/hom/schwertmannite.pdf Mineral Handbook
  4. Bigham, JM, Carlson, L, Murad, E (1994) Schwertmannite, a new iron oxyhydroxysulfate from Pyhasalmi, Finland, and other localities. Mineral Mag 58, 641-664
  5. 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.
  6. 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
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