Ruby
Variety Al2O3
About it
Red corundum coloured by chromium, second only to diamond in hardness. Myanmar (Mogok), Mozambique, and Thailand are famous sources; most rubies are heated, and some are glass-filled.
- Type
- Variety
- Group
- Corundum variety
- Formula
- Al2O3
- Hardness (Mohs)
- 9
- Specific gravity
- 3.95–4.05
- Streak
- white
- Lustre
- adamantine (diamond-like), vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- red, pinkish red, purplish red
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- none; parting common; conchoidal to uneven fracture
- Under UV light
- often strong red under longwave UV; iron-rich rubies glow less
Typical values: real specimens vary. For more, see mindat.org.