White single crystal of the extremely rare Mn-Mg-Zn mineral gerstmannite from the type and only known locality worldwide in Sterling Hill mine, Ogdensburg, New Jersey. The sample is from the original find of the mineral at Sterling Hill in 1970 when the only two known specimens were found. This is a fragment of one of these two larger specimens, so it is a cotype specimen Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Gerstmannite
Gerstmannite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mn²⁺MgZn(SiO₄)(OH)₂.
It crystallizes in the orthorhombic crystal system (space group Bbcm).
Key properties: Mohs hardness 4.5; specific gravity 3.68; White streak; Vitreous to subadamantine, silky when matted luster; optically biaxial.
IMA symbol Gmn, IMA status: approved, named in 1975.
Found in a hydrothermal vein cutting franklinite-willemite ore in a metamorphosed stratiform zinc orebody.
It is found associated with Calcite, manganpyrosmalite, sphalerite.
The name refers to Ewald Gerstmann (1918{), mineral collector of Franklin, New Jersey, USA.