Formula: ZnAl2O4 multiple oxide, spinel group, forms a series with hercynite and with spinel
Specific gravity: 4.57
Hardness: 7½ to 8
Colour: Dark blue-green, yellow, brown, black
Common impurities: Fe,Mg
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
It is formed by the low-grade metamorphism of bauxite (HOM).
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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