Group of colourless rösslerite crystals on white brassite from the famous locality of Jachymov (Bohemia, Czech Republic). — Photo: David Hospital · CC BY-SA 4.0
Rösslerite
Rösslerite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Mg(AsO₃OH)·7H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 2–3; specific gravity 1.943; Vitreous to dull luster; optically biaxial.
IMA symbol Rö, grandfathered status — known before the IMA’s founding, named in 1861.
Found as a secondary mineral in the oxidized zone of arsenic-bearing ore deposits.
It is found associated with Pharmacolite, haidingerite, picropharmacolite, erythrite.
The mineral was named to honor Karl Rössler, Hanau, Germany.