Opal
Nature's kaleidoscope — a play of spectral fire locked in hydrated silica.
Opal is a hydrated amorphous form of silica, distinguished by its unique 'play of color' — a phenomenon caused by the diffraction of light through microscopic spheres of silica within the stone's structure. Unlike crystalline gemstones, opal contains 3–21% water, which contributes to both its beauty and its fragility. Black opal from Lightning Ridge, Australia, is the most valuable variety, while Ethiopian opal has disrupted the market with stunning material at more accessible prices. Opal is one of the few gemstones that cannot be reliably synthesized with the same optical properties as natural material.
Physical Properties
| Hardness (Mohs) | 5.5–6.5 |
| Refractive Index | 1.37–1.47 |
| Specific Gravity | 1.98–2.50 |
| Crystal System | Amorphous |
| Chemical Formula | SiO₂·nH₂O |
Color Varieties
Major Sources
Australia (90%+ of world supply) · Ethiopia · Mexico · Brazil · USA (Nevada)
Pricing Factors
Body Tone
Black opals are the most valuable because the dark body tone makes the play of color more vivid. Light/white opals are more common and affordable.
Play of Color
The range, intensity, and pattern of spectral colors determine value. Red play of color is the rarest and most valuable, followed by orange, then green and blue.
Pattern
Harlequin (large mosaic patches) is the most prized pattern. Broad flash, pinfire, and rolling flash are also valued. Random or weak patterns are discounted.
Origin
Lightning Ridge black opals are the benchmark. Ethiopian opals are more affordable but can be hydrophane (absorb water), which affects stability.
Care Instructions
Do
- Clean with a damp soft cloth only
- Store with a damp cotton ball in an airtight container in dry climates
- Wear regularly — body oil helps maintain moisture content
Don't
- Never use ultrasonic or steam cleaners
- Don't soak in water (especially Ethiopian opal)
- Don't store in direct sunlight or heat — dehydration causes crazing (cracking)
Cleaning Method
A damp soft cloth only. Opal is extremely sensitive to heat, chemicals, and dehydration. Never submerge, especially Ethiopian varieties.
Insider Buying Tips
Australian black opal from Lightning Ridge is the gold standard — pay the premium if you can.
Ethiopian opal offers incredible play of color at a fraction of Australian prices, but be aware of hydrophane behavior.
Avoid opal doublets and triplets unless deliberately buying for budget — they're assembled stones, not solid opal.
View opals from multiple angles and in different lighting to assess the full play of color.
For rings, choose a protective bezel setting rather than prongs to shield the soft stone.
Did You Know?
Australia produces over 90% of the world's opals, mostly from the Outback mining towns of Lightning Ridge, Coober Pedy, and Andamooka.
The 'Olympic Australis,' found in 1956, is the largest and most valuable opal ever discovered at 17,000 carats.
In the Middle Ages, opal was considered lucky — the superstition of it being unlucky originated from a Walter Scott novel in 1829.