Franklinite
Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula Zn2+Fe23+O4.
| Franklinite | |
|---|---|
 Franklinite (black) with willemite (red) and calcite (white) | |
| General | |
| Category | Oxide minerals Spinel group Spinel structural group |
| Formula (repeating unit) | 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 | |
| Color | black |
| Crystal habit | octahedral |
| Cleavage | None; indistinct octahedral parting in four directions |
| Fracture | irregular/uneven, conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5+1⁄2-6 |
| Luster | metallic, often dull |
| Streak | reddish brown to black |
| Diaphaneity | opaque |
| Specific gravity | 5.07 - 5.22 |
| Ultraviolet fluorescence | None |
| Solubility | HCl soluble |
| Other characteristics | magnetic |
| References | [2] |
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 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 is a major ore of the element zinc. 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]
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References
- 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.
- Chesterman, Charles W. (1978). The Audubon Society field guide to North American rocks and minerals. New York: Alfred A. Knopf. p. 418. ISBN 0394502698.
- "Office of the Governor | Governor Murphy Signs Legislation Designating Franklinite as State Mineral". www.nj.gov. Retrieved 2023-07-20.
