Opal is hydrated silica, famous for flashes of color that move as the stone turns. Precious opal shows play-of-color; common opal does not. A warm orange fire opal may be attractive for its body color even when it has no play-of-color, so those names describe different features.
Structure creates the changing color
Opal does not have the regular crystal structure of quartz. In precious opal, an ordered internal arrangement can diffract visible light into changing colors. Body color, pattern, brightness, and the area over which the effect remains visible all matter. A spectacular patch in one photograph may disappear at another angle. Opal is not ordinarily described by the birefringence and pleochroism of crystalline gems. Its hardness is roughly 5–6½, and water content and behavior vary between materials.
Solid stone, assembly, and care
A solid opal, a doublet, and a triplet are different constructions. An assembled stone can place a thin opal layer over a backing or beneath a protective cap; ask for a clear description. Synthetic opal and imitations also require accurate naming. Some opal receives smoking, dyeing, impregnation, or other treatment, and porous hydrophane material needs particular care around liquids. Avoid sudden temperature changes and harsh cleaning. Do not assume every opal should be soaked or oiled. Compare the entire face in a moving view, inspect edges and any cracking, and obtain care advice for the actual stone and mounting.
Opal is hydrated silica and does not have the regular crystal structure of quartz. Precious opal’s play-of-color is distinct from the iridescence of fire agate. Ask whether a piece is solid opal, an assembled doublet or triplet, or another product: construction and treatment can change care and comparison.
For a purchase involving a consequential identity or treatment claim, the natural gemstone buying guide explains evidence and comparison. Our treatment disclosure guide distinguishes a known treatment from an assumption.
Gems Jewelry specializes mainly in natural faceted sapphires and rubies. For the stones currently offered, explore the collections. Availability of another gemstone type should be confirmed directly.