Gahnite

gahnite

pyrrhotite

spinel

hercynite

Images

Formula: ZnAl2O4 Multiple oxide, spinel group, forms a series with hercynite and with spinel
Specific gravity: 4.57
Hardness: 7½ to 8
Streak: Grey
Colour: Dark blue-green, yellow, brown, black
Common impurities: Fe,Mg
Environments:

Pegmatites
Metamorphic environments

Gahnite occurs in crystalline schist, in granite pegmatites especially those rich in lithium, and in contact metamorphosed limestone. It also occurs in high temperature replacement ore deposits in schist or marble (Dana).
It is formed by the low-grade metamorphism of bauxite (HOM).

Localities

At the Geco Mine, Gemmell Township, Thunder Bay District, Ontario, Canada, gahnite is associated with corundum, pyrrhotite, ferronigerite, phlogopite, staurolite, cordierite, pyrite and chalcopyrite (HOM).

The type locality is the Falun mine, Falun, Dalarna County, Sweden.

At Franklin, Franklin Mining District, Sussex County, New Jersey, USA, gahnite is associated with rhodonite, franklinite, calcite, andradite and willemite (HOM).

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