Schwertmannite

Schwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of Fe8O8(OH)6(SO4) · n H2O or Fe3+
16O
16(OH,SO4)
12–13·10-12H
2O.[2] 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.[3]

Schwertmannite
General
CategorySulfate minerals
Formula
(repeating unit)		Fe8O8(OH)6(SO4) · n H2O
IMA symbolSwm[1]
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[2][3]

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.[4]

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.[5] However, it is more commonly reported as an orange precipitate in streams and lakes affected by acid mine drainage.[6] Schwertmannite is also known to be central to iron-sulfur geochemistry in acid sulfate soils associated with coastal lowlands.[7]

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mindat
  3. http://webmineral.com/data/Schwertmannite.shtml Webmineral
  4. http://rruff.geo.arizona.edu/doclib/hom/schwertmannite.pdf Mineral Handbook
  5. Bigham, JM, Carlson, L, Murad, E (1994) Schwertmannite, a new iron oxyhydroxysulfate from Pyhasalmi, Finland, and other localities. Mineral Mag 58, 641-664
  6. 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.
  7. 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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