Bronze brown metallic crystals of the very rare Ag-Fe-Ni sulphide mineral argentopentlandite from a locality in Michigan (Silver City, Ontonagon County, Michigan, United States of America) in a partially polished specimen that was analyzed by the former owner of the specimen (the Vandenbroucke Museum, but the analysis is no longer available). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Argentopentlandite
Argentopentlandite is an IMA-recognized mineral species in the sulfide class, with the chemical formula Ag(Fe,Ni)₈S₈.
It crystallizes in the cubic crystal system (space group Fm3m). It is a member of the Pentlandite structural group.
Key properties: specific gravity 4.66; Metallic. R: (400) 20.4, (420) 21.0, (440) 21.9, (460) 22.9, (480) 24.2, (500) 25.6, (520) 27.2, (540) 28.8 luster.
IMA symbol Apn, IMA status: approved, named in 1970.
Found in pyrite and cubanite-chalcopyrite hydrothermal veins in ultramafic rocks and in skarn; in hydrothermal veins in acidic volcanics; rare in carbonatites.
It is found associated with Pyrite, pyrrhotite, mackinawite, cubanite, chalcopyrite, stannite, galena, sphalerite, calcite, quartz.
The name refers to the similarity in composition to pentlandite.