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Formula: Mn2+Fe3+2O4
Multiple oxide, spinel subgroup,
manganese-bearing mineral
Jacobsite forms a series with magnetite
Crystal System: Isometric
Specific gravity: 4.76 measured, 5.03 calculated
Hardness: 5½ to 6½
Streak: Reddish black or brownish black
Colour: Black, gray in reflected light
Epitaxy: Jacobsite forms oriented intergrowths with hausmannite.
Common impurities: Zn
Environments:
Sedimentary environments
Metamorphic environments
Jacobsite is a primary mineral or a
secondary alteration product of other
manganese-bearing minerals in some metamorphosed
manganese deposits, associated with
hausmannite,
galaxite, braunite,
pyrolusite, coronadite,
hematite or magnetite
(HOM).
In Sweden jacobite occurs in crystalline limestone with
native copper at the Jakobsberg mine, and with
tephroite and
calcite at Långban
(Dana).
The Hutter Mine locality, Pittsylvania County, Virginia, is a metamorphosed
magnetite deposit, with subsidiary
manganoan marble, that
occurs in schist.
Manganese oxides and
spinel group minerals at the Hutter Mine include
hausmannite, magnetite,
galaxite and jacobite. It seems that the maximum temperature
developed here was 550 to 600oC
(AM87.690).
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