Boulder 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 filling seams and cracks in brown ironstone boulders from western Queensland, Australia, cut with the ironstone left as a natural backing. Yowah nuts are a small, nut-shaped form.
- 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
- blue, green, and red flashes on brown ironstone
- Transparency
- opaque
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.