Mcgovernite Locality: Sterling Mine, Sterling Hill , Ogdensburg , Franklin Mining District, Sussex County, New Jersey , USA ( Locality at mindat.org ) Size: 3.5 x 2.7 x 1.9 cm. Mcgovernite is a very rare arsenate, unique in the world to the Sterling Mine of New Jersey. Mcgovernite is also the mineral species with the largest number of atoms in the unit cell. This specimen is extremely rare and exceptional, in that much of the piece consists of lustrous, bronzy-brown crystal plates, along with aggregates of mcgovernite. Crystals reach 5 mm. Mcgovernite usually occurs as thin coatings or as radiating spherical sprays of crystals. This extreme rarity is very well crystallized for the species. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Mcgovernite
Mcgovernite is an IMA-recognized mineral species in the silicate class, with the chemical formula Zn₃(Mn²⁺,Mg,Fe³⁺,Al)₄₂(As³⁺O₃)₂(As⁵⁺O₄)₄[(Si,As⁵⁺)O₄]₈(OH)₄₂.
It crystallizes in the hexagonal crystal system (space group R-32/c). It is a member of the Hematolite structural group.
Key properties: Mohs hardness 3; specific gravity 3.719; Pearly luster; optically uniaxial.
IMA symbol Mgv, grandfathered status — known before the IMA’s founding, named in 1927.
Occurs as the principal filling of a vein in massive zinc ore in a metamorphosed stratiform Zn-Mn deposit.
It is found associated with Franklinite, willemite, zincite, calcite.
The name refers to J.J. McGovern (?{1915), of Franklin, New Jersey, USA, prominent collector of Franklin minerals.