Hodgkinsonite Locality: Franklin Mine , Franklin , Franklin Mining District, Sussex County, New Jersey , USA ( Locality at mindat.org ) Size: 4.9 x 4.4 x 3.2 cm. Hodgkinsonite is a very rare manganese, zinc silicate found only in the Franklin Mining District of New Jersey. The sculptural franklinite with a vein of willemite matrix hosts a vein and vugs filled with sharply crystallized, pink hodgkinsonite crystals. The translucent and lustrous crystals reach 8 mm and the main crystal here is doubly terminated. These are large crystals and this is a very rich example for the species and locality. Moreover, it is a good display specimen instead of the typical chunk of ugly rock. Rarely available, this is one from an old collection sold at the Rochester Sypmosium last year (2008). Ex. Ranstrom Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Hodgkinsonite
A rare pink-to-red zinc-manganese silicate forming radiating monoclinic prisms at Franklin, New Jersey.
Intro adapted from Wikipedia (CC BY-SA).
Hodgkinsonite is an IMA-recognized mineral species in the silicate class, with the chemical formula Zn₂Mn²⁺(SiO₄)(OH)₂.
It crystallizes in the monoclinic crystal system (space group P2_1/a).
Key properties: Mohs hardness 5; specific gravity 4.06–4.08; refractive index 1.736; optically biaxial.
IMA symbol Hgk, grandfathered status — known before the IMA’s founding, named in 1913.
Occurs as seams in massive willemite-franklinite granular ore in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA).
It is found associated with Barite, willemite, franklinite, tephroite, pyrochroite, calcite, manganoan garnet, copper.
The name refers to H.H. Hodgkinson, Assistant Underground Superintendent of the Franklin mine, who discovered the mineral.