Gahnite
Gahnite is one associated with the rarer people of the Spinel group of minerals. It is available at many zinc deposits worldwide. Crystals are typically very small, included and just translucent to opaque, but faceted gems are collectable due to their color and rarity. Present sources are Australia, Brazil, Germany, Italy, Namibia, Nigeria, Sweden, as well as in the united states in Sussex County, NJ-new jersey, Carroll County, Maryland, Mitchell County, North Carolina and Fremont County, Colorado.
| Category: | Oxide minerals Spinel group Spinel structural group |
| Chemical Formula: | ZnAl2O4 |
| Crystallography: | Isometric – Hexoctahedral |
| Crystal Habit: | Crystals typically octahedra, rarely as dodecahedra, may be modified, to 12 cm; also as exsolution lamellae in other minerals; granular, massive. |
| Twinning: | On [111] as both twin and composition plane, common |
| Cleavage: | [111] Indistinct |
| Fracture: | Conchoidal also Irregular, Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 7.5 – 8.0 |
| Density: | 4.00 – 4.64 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Dark Bluish Green, Grayish Green, Deep Green, Greenish Black, Bluish Black |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous (glassy) |
| Refractive Index: | 1.82 Isotropic (1.790 – 1.820 due to impurities) |
| Birefringence: | 0.00 Isotropic |
| Dispersion: | n/a |
| Pleochroism: | n/a |
