Definition
A hydrated silica prized for play-of-color that flashes spectral hues.
Key Features
- Mohs hardness about 5.5 to 6.5 with fair toughness
- Types include white, black, crystal, and boulder opal
- Play-of-color arises from silica sphere diffraction
- Often cut as cabochons to showcase color
Origin and History
Major sources include Australia and Ethiopia with Mexico known for fire opal. Black opals from Lightning Ridge are especially prized.
Buying Guide
Evaluate body tone, brightness, pattern, and coverage of play-of-color. Avoid dryness and obvious cracks.
- Seek strong brightness visible across the face
- Check for crazing or cracks especially in some hydrophane opals
- Prefer stable material with reputable disclosure
Care and Maintenance
Avoid ultrasonic cleaners, heat, and prolonged dehydration. Clean gently with soft cloth and mild soap.
Related Comparisons
FAQs
Why does opal show rainbow colors
Regular arrays of silica spheres diffract light to produce play-of-color.
Can opal dry out and crack
Some opals are sensitive to dehydration. Store in stable environments and avoid extremes.
Is Ethiopian opal hydrophane
Many are. They can absorb water temporarily changing appearance.