Gahnite
Mineral ZnAl2O4
Also called Zinc spinel and Automolite
About it
Dark green to blue-black octahedrons, harder than quartz, in granite pegmatites and zinc ore bodies. Known from Franklin, New Jersey, Broken Hill, Australia, and the pegmatites of Brazil.
- Type
- Mineral
- Group
- Oxide, spinel group
- Formula
- ZnAl2O4
- Hardness (Mohs)
- 7.5–8
- Specific gravity
- 4–4.6
- Streak
- grey
- Lustre
- vitreous (glassy)
- Crystal system
- Isometric (cubic)
- Colours
- dark green, blue-green, blue, black, yellow-brown
- Transparency
- translucent, opaque
- Cleavage and fracture
- indistinct octahedral; conchoidal to uneven fracture
Typical values: real specimens vary. For more, see mindat.org.