Star sapphire
Variety Al2O3
About it
Sapphire cut as a dome to show a six-rayed star (asterism) from aligned rutile needles. Sri Lanka, Myanmar, and Thailand are known sources; flawless, very sharp stars often mean a synthetic.
- 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
- blue, grey, black, purple, yellow
- Transparency
- translucent, opaque
- Cleavage and fracture
- none; parting common; conchoidal to uneven fracture
Typical values: real specimens vary. For more, see mindat.org.