Spinel
Mineral MgAl2O4
Also called Balas ruby, Pleonaste, and Ceylonite
About it
Hard octahedrons, often twinned flat, in marble and gem gravels. Red spinel was long mistaken for ruby; fine crystals come from Myanmar, Sri Lanka, Tajikistan, and Luc Yen in Vietnam.
- Type
- Mineral
- Group
- Oxide, spinel group
- Formula
- MgAl2O4
- Hardness (Mohs)
- 7.5–8
- Specific gravity
- 3.55–4.1
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Isometric (cubic)
- Colours
- red, pink, blue, violet, black, green, grey
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- none; octahedral parting, conchoidal fracture
- Under UV light
- red and pink stones glow red under longwave UV
Typical values: real specimens vary. For more, see mindat.org.