White silky spherules composed of acicular crystals of the extremely rare Mn arsenate mineral sterlinghillite from the TL in Sterling Hill mine (Sterling Mine, Ogdensburg, Sussex County, New Jersey, United States of America) and only one of the three known localities worldwide. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Sterlinghillite
Sterlinghillite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Mn²⁺₃(AsO₄)₂·3H₂O.
It crystallizes in the monoclinic crystal system.
Key properties: Mohs hardness 3; specific gravity 2.95; White streak; Dull to silky luster; optically biaxial.
IMA symbol Slg, IMA status: approved, named in 1980.
Found as a very rare mineral in seams in franklinite ore from a metamorphosed stratiform zinc orebody.
It is found associated with Franklinite, sphalerite, löllingite, calcite.
The name refers to the Sterling Hill mine, New Jersey, USA.