Brandtite Locality: Fuchs Quarry, Hartkoppe Mt., Sailauf, Hösbach, Spessart Mts, Franconia, Bavaria, Germany Field of view 5 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Brandtite
Brandtite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂Mn²⁺(AsO₄)₂·2H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Roselite structural group.
Key properties: Mohs hardness 3.5; specific gravity 3.61–3.67; Vitreous luster; optically biaxial.
IMA symbol Bdt, grandfathered status — known before the IMA’s founding, named in 1888.
Found in metamorphosed Fe–Mn orebody (Harstigen mine and Långban, Sweden); in a metamorphosed stratiform zinc orebody (Sterling Hill, New Jersey, USA).
It is found associated with Lead, sarkinite, flinkite, caryopilite, galena, barite, calcite (Harstigen mine, Sweden); sarkinite, rhodochrosite, sphalerite, franklinite, willemite, barite.
The mineral was named to honor George Brandt (1694–1768), Swedish chemist.