| Gahnite | |
|---|---|
| General | |
| Category | Oxide mineral - spinel group |
| Chemical formula | ZnAl2O4 |
| Strunz classification | 04.BB.05 |
| Identification | |
| Color | Dark green, bluish green, blue to indigo, yellow to brown |
| Crystal habit | Typically octahedra, rarely as dodecahedra also assive to granular |
| Crystal system | Isometric |
| Twinning | Common on [111] produces striations |
| Cleavage | Indistinct parting on [111] |
| Fracture | Conchoidal, uneven |
| Mohs scale hardness | 7.5–8.0 |
| Luster | Vitreous |
| Streak | Grey |
| Diaphaneity | Translucent to nearly opaque |
| Specific gravity | 4.38–4.60 |
| Optical properties | Isotropic |
| Refractive index | n = 1.79–1.80 |
| References | [1][2][3] |
Gahnite, ZnAl2O4, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It occurs in Falun, Sweden where it is found in pegmatites and skarns, contact metamorphic rocks. Other occurrences include Charlemont, Massachusetts; Spruce Pine, North Carolina; White Picacho district, Arizona; Topsham, Maine; and Franklin, New Jersey in the United States.[1][2]
It was first described in 1807 for an occurrence in the Falu mine, Falun, Dalarna, Sweden, and named after the Swedish chemist, Johan Gottlieb Gahn (1745-1818), the discoverer of the element manganese.[3][2] It is sometimes called zinc spinel.