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Formula: Mn7Si6O15(OH)8 (oxidation state of manganese is Mn2+)
Phyllosilicate, manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.9 to 3.1 measured
Hardness: 6
Streak: White
Colour: Brown, dark brown, golden brown, greyish-yellow
Common impurities: Al,Fe,Zn,Mg,Ca
Environments
Bementite is found in low-grade metamorphic manganese silicate deposits
(Mindat).
Localities
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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