Franklinite

Franklinite
240px Franklinite (black) with Zincite (red)
General
Category	Oxide minerals Spinel group Spinel structural group
Formula (repeating unit)	ZnFe2O4
Strunz classification	04.BB.05
Identification
Color	black
Crystal habit	octahedral
Crystal system	isometric/cubic
Fracture	irregular/uneven, conchoidal
Mohs scale hardness	5½-6
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.

See also

• Spinel
• Classification of minerals
• List of minerals

References

• Mindat page for franklinite

External links

Media related to at Wikimedia Commons