Schwertmannite
A brownish-yellow iron oxyhydroxy-sulfate — the hallmark crust of acid mine drainage.
Intro adapted from Wikipedia (CC BY-SA).
Schwertmannite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Fe³⁺₁₆O₁₆(OH)₉.₆(SO₄)₃.₂·10H₂O.
It crystallizes in the triclinic crystal system (space group P4/m). It is a member of the Coronadite structural group.
Key properties: Ocher-yellow streak.
IMA symbol Swm, IMA status: approved, named in 1990.
A secondary mineral precipitated by waters of pH 3–4.5 and high in iron sulfate content from the surface oxidation of metal sulfides.
It is found associated with Goethite, jarosite, natrojarosite, ferrihydrite, sulfides.
The name refers to Udo Schwertmann (1927–), Professor of Soil Science, Technical University of Munich, Munich, Germany, who has worked on poorly crystalline products of weathering.