| Franklinite | |
| Category: | Oxide minerals Spinel group Spinel structural group |
| Formula: | ZnFe2O4 |
| Imasymbol: | Frk[1] |
| Strunz: | 4.BB.05 |
| System: | Cubic |
| Class: | Hexoctahedral (mm) H-M symbol: (4/m 2/m) |
| Symmetry: | Fdm |
| Color: | black |
| Habit: | octahedral |
| Cleavage: | None; indistinct octahedral parting in four directions |
| Fracture: | irregular/uneven, conchoidal |
| Tenacity: | Brittle |
| Mohs: | 5.5–6 |
| Luster: | metallic, often dull |
| Streak: | reddish brown to black |
| Diaphaneity: | opaque |
| Gravity: | 5.07–5.22 |
| Fluorescence: | None |
| Solubility: | HCl soluble |
| Other: | magnetic |
| References: | [2] |
Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula Zn2+Fe23+O4.
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]