Blue crystals of the extremely rare mineral mahnertite from the type locality for the mineral (Cap Garonne, Var, Provence-Alpes-Cote d'Azur, France). — Photo: David Hospital · CC BY-SA 4.0
Mahnertite
Mahnertite is an IMA-recognized mineral species in the arsenate class, with the chemical formula (Na,Ca,K)Cu₃(AsO₄)₂Cl·5H₂O.
It crystallizes in the tetragonal crystal system (space group I4/mmm).
Key properties: Mohs hardness 2–3; specific gravity 3.33; Pale blue streak; Vitreous luster; optically uniaxial.
IMA symbol Mah, IMA status: approved, named in 1994.
Found in the oxidized zone of an arsenic-rich copper deposit (Cap Garonne mine, France).
It is found associated with Tennantite, covellite, geminite, pushcharovskite, quartz (Cap Garonne mine, France).
The mineral was named to honor Dr. Volker Mahnert (b. 1943), Director, Natural History Museum, Geneva, Switzerland.