Franklinite

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Franklinite
Franklinite-Willemite-Zincite-103826.jpg
Franklinite (black) with Zincite (red)
General
Category Oxide minerals
Spinel group
Spinel structural group
Formula ZnFe2O4
IMA symbol Frk [1]
Strunz classification 4.BB.05
Crystal system Cubic
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Identification
Colorblack
Crystal habit octahedral
Cleavage None; indistinct octahedral parting in four directions
Fracture irregular/uneven, conchoidal
Tenacity Brittle
Mohs scale hardness5.5–6
Luster metallic, often dull
Streak reddish brown to black
Diaphaneity opaque
Specific gravity 5.07–5.22
Ultraviolet fluorescence None
Solubility HCl soluble
Other characteristicsmagnetic
References [2]

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

Contents

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 uranium, sulfuric acid, and mercury. It is named after its local discovery at the Franklin Mine and Sterling Hill Mines in New Jersey.

In 2023, Franklinite was designated the state mineral of New Jersey. [3]

A microscopic picture of Franklinite Frankelinite Zincate red (Normal and Polarized).jpg
A microscopic picture of Franklinite

See also

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. Chesterman, Charles W. (1978). The Audubon Society field guide to North American rocks and minerals. New York: Alfred A. Knopf. p. 418. ISBN   0394502698.
  3. "Office of the Governor | Governor Murphy Signs Legislation Designating Franklinite as State Mineral". www.nj.gov. Retrieved 2023-07-20.

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