Opal

Opal is hydrated silica — silicon dioxide with up to 21 % water locked in its structure. The play-of-color (the flashing rainbow effect) comes from microscopic silica spheres diffracting light, the same physics as a butterfly wing or a peacock feather.

Opal is soft, water-bearing, and the most temperamental of the commonly-worn gemstones. Sudden temperature change can crack it; dry storage can craze it; humidity is its natural state. It’s also unlike any other stone you can buy.

Precious vs common opal

The trade splits opal into two grades by whether it shows play-of-color:

• Precious opal — shows distinct color flashes that move as the stone is rotated.
• Common opal — solid body color, no play-of-color. Usually called “potch” in the trade.

Within precious opal, three main body-color categories:

Doublets and triplets

Because precious opal is often found as thin seams in rock, the trade developed assemblies that turn small slices into wearable stones:

• Solid opal — one continuous piece. The premium choice. Worth the most, doesn’t degrade over time.
• Doublet — a thin opal slice glued to a dark backing (usually black potch or onyx) to enhance the play-of-color.
• Triplet — opal slice sandwiched between a dark backing and a clear quartz or glass top cap. Cheapest, most fragile, can fog if it contacts water at the seam.

A reputable seller discloses doublet/triplet construction in writing. Don’t buy a doublet/triplet as a solid stone — the price gap is 3–10×.

Care

The single most important rule: don’t shock it.

• No sudden temperature changes. Cold-to-hot or hot-to-cold can fracture the silica matrix.
• No ultrasonic or steam cleaners. Ever. They’ll destroy any opal, solid or assembled.
• Solid opal can tolerate brief contact with water; doublets and triplets generally cannot.
• Ethiopian opal is “hydrophane” — it absorbs water, becomes translucent and loses play-of-color until it dries. Recovers fully when dry, but startling on first encounter.

Store opal away from extreme heat (direct sun on a windowsill cracks it) and direct dry environments (a desert hotel safe will craze it over a week).

Buying

A working buyer checks three things:

1. Construction — solid? Doublet? Triplet? Insist on disclosure.
2. Play-of-color quality — broad flashes are more prized than pinfire (tiny dots). Patterns called “harlequin” (square mosaic) and “rolling flash” (sheets of color that move as you tilt) command premiums.
3. Body color saturation — for black opal, darker is better. Test by viewing the stone face-up against a neutral background; the darker the “floor” behind the colors, the more dramatic the stone.