Precious opal
Variety SiO2·nH2O
Also called Noble opal
Take care.
- Sensitive to heat: Keep it away from heat and sudden changes of temperature, including hot lights and ultrasonic cleaners.
About it
Opal that flashes spectral colours (play-of-colour) from an orderly stack of tiny silica spheres. Australia supplies most, from Coober Pedy, Lightning Ridge, and Queensland; keep it from heat and sudden drying.
- Type
- Variety
- Group
- Opal variety
- Formula
- SiO2·nH2O
- Hardness (Mohs)
- 5.5–6.5
- Specific gravity
- 1.98–2.25
- Streak
- white
- Lustre
- vitreous (glassy), resinous
- Crystal system
- Amorphous (no crystal structure)
- Colours
- white, grey, black, colourless, with play-of-colour
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.