| Schwertmannite | |
| Category: | Sulfate minerals |
| Imasymbol: | Swm[1] |
| Strunz: | 7.DE.15 |
| System: | Tetragonal Dipyramidal class |
| Symmetry: | Tetragonal H-M symbol: (4/m) Space group: P4/m |
| Color: | brownish yellow |
| Luster: | earthy |
| Streak: | yellow |
| Diaphaneity: | opaque |
| References: | [2] [3] |
Schwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of or .[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]