Brownish grey single crystal group of the extremely rare Cu-As selenide mgriite from the type and only known locality worldwide in Saxony: Schlema-Hartenstein, Erzgebirge, Saxony, Germany. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Mgriite
Mgriite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Cu₃AsSe₃.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Diamond structural group.
Key properties: specific gravity 4.9; Metallic. R: (420) 27.1, (460) 26.7, (500) 26.4, (540) 26.9, (580) 27.0, (620) 26.8, (660) 26.4, (700) 26.0 luster.
IMA symbol Mgi, IMA status: approved, named in 1980.
Found in hydrothermal veins.
It is found associated with Clausthalite, berzelianite, umangite, ankerite, calcite.
The name comes from the first letters of Moscow Geological Exploration Institute [Moskovskogo Geologro Razvedounogo Instituta (MGRI)] the laboratory in which the mineral was discovered.