Hercynite
Mineral FeAl2O4
About it
Black to dark green octahedral grains of iron spinel, very hard, in metamorphic rocks and emery. Named for the Hercynian Forest of Bohemia, where it was first found.
- Type
- Mineral
- Group
- Oxide, spinel group
- Formula
- FeAl2O4
- Hardness (Mohs)
- 7.5–8
- Specific gravity
- 3.95–4.4
- Streak
- dark green
- Lustre
- vitreous (glassy)
- Crystal system
- Isometric (cubic)
- Colours
- black, dark green, dark brown
- Transparency
- opaque, translucent
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.