Black opal
Variety SiO2·nH2O
Take care.
- Sensitive to heat: Keep it away from heat and sudden changes of temperature, including hot lights and ultrasonic cleaners.
About it
Precious opal with a dark body that makes its play-of-colour glow; the most valuable kind. Lightning Ridge in New South Wales is the classic source; doublets and triplets imitate it with a dark backing.
- 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
- black, dark grey, dark blue, with play-of-colour
- Transparency
- translucent, opaque
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.