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]
It was first described for an occurrence in Finland in 1994 and named for Udo Schwertmann (born 1927), a soil scientist at the Technical University of Munich, Munich, Germany.[4]
Schwertmannite (with a distinct "pin cushion" morphology) commonly forms in iron-rich, acidic 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]
^Bigham, JM, Carlson, L, Murad, E (1994) Schwertmannite, a new iron oxyhydroxysulfate from Pyhasalmi, Finland, and other localities. Mineral Mag 58, 641-664
^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.
^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
