Formula: Mn7Si6O15(OH)8 (oxidation state of manganese is Mn2+)
Unclassified silicate, manganese-bearing mineral
Specific gravity: 2.9 to 3.1
Colour: Brown, dark brown, golden brown, greyish-yellow
Common impurities: Al,Fe,Zn,Mg,Ca
Bementite is found in low-grade metamorphic manganese silicate deposits
The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. Bementite is a primary silicate found in small amounts in altered granite, intimately associated with hausmannite and tephroite (AJM 22.1.33).
At the Hale Creek Mine, Mad River Rock, Coastal Range, Trinity county, California, USA, bementite is associated with hausmannite, rhodochrosite and inesite (HOM).
At the type locality, the Trotter Mine, Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA, bementite was found layered parallel to the walls of secondary veins of calcite in a zinc-iron oxide ore deposit hosted in marble, associated with calcite and willemite (HOM, Mindat).
On the Olympic Peninsula at a number of small deposits in Clallan, Jefferson, and Mason counties, Washington, USA, bementite is associated with hausmannite, jacobsite, braunite, alleghanyite, baryte, grossular, johannsenite and calcite (HOM).
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