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Franklinite (black) with Zincite (red)
Category Oxide minerals
Spinel group
Spinel structural group
(repeating unit)
Strunz classification 4.BB.05
Crystal system Cubic
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Color black
Crystal habit octahedral
Fracture irregular/uneven, conchoidal
Mohs scale hardness 5 12-6
Luster metallic, often dull
Streak reddish brown to black
Diaphaneity opaque
Specific gravity 5.07 - 5.22
Solubility HCl soluble
Other characteristics magnetic

Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula ZnFe3+2O4.

As with another spinel member magnetite, both ferrous (2+) and ferric (3+) iron may be present in Franklinite samples. Divalent iron and/or manganese (Mn) may commonly accompany zinc (Zn) and trivalent manganese may substitute for some ferric iron.

At its type locality, Franklinite can be found with a wide array of minerals, many of which are fluorescent. More commonly, it occurs with willemite, calcite, and red zincite. In these rocks, it forms as disseminated small black crystals with their octahedral faces visible at times. It may rarely be found as a single large euhedral crystal.

Franklinite was a minor ore of zinc, manganese, and iron. It is named after its local discovery at the Franklin Mine and Sterling Hill Mines in New Jersey.

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External links[edit]

Media related to Franklinite at Wikimedia Commons