Blue Opal

Extended geology

Blue opal is a hydrated form of silica with the general formula SiO2 nH2O, where n represents the variable amount of water in the structure. Unlike crystalline quartz, opal is amorphous, meaning its silica molecules are arranged randomly rather than in a repeating geometric pattern. This randomness is why opal feels different from quartz and why it can be worked so smoothly.

In Peruvian blue opal, the blue comes from tiny inclusions of chrysocolla or other copper silicates spread through the silica; copper can reach about one percent of the stone. The amount of water in blue opal ranges from about 3 to 21 percent by weight, usually 6 to 10 percent, and this water is not loosely bound but rather integrated into the mineral structure. This is crucial for understanding why blue opal can develop crazing if it loses water gradually over years, and why extreme dryness is a concern.

Blue opal forms in weathered volcanic rock, in zones where silica-rich groundwater moves slowly through fractures and porous zones, depositing silica as the water evaporates or reacts with surrounding material. This process takes thousands to millions of years. The result is massive opal, never as distinct crystals, and always worked from larger rough material into finished pieces.

Water content and preservation

The water in blue opal is not a flaw, it's structural. This water keeps the stone soft and slightly translucent. However, if opal is stored in extremely dry conditions for extended periods, it can lose water and develop fine surface cracks called crazing. This does not mean the stone is broken, but it does affect appearance and can make the piece feel less smooth to the touch. Conversely, soaking opal in water does not restore crazing, and extended water immersion can soften the stone further.

For long-term care, store blue opal in a normal humidity environment. A velvet pouch or soft cloth pouch kept in a drawer, shelf, or display case at room humidity is ideal. Avoid storing it in plastic bags sealed for months, in dry rooms heated intensely in winter, or exposed to direct sun which can gradually fade the color.

Extended sourcing

Peru's Andean blue opal comes from weathered volcanic deposits in the Andes mountains, accessed through small-scale hand-mining operations. The color tends toward pale, cool blue with a milky translucence. Material is sorted by hand before it leaves the mining zone, and finished pieces are typically tumbled or cabochon-cut. Sourcing relationships with our primary source have been established over years, allowing us to confirm mining practices and labor conditions with reasonable confidence.

Oregon's blue opal comes from high desert deposits in the state's interior. The material tends toward slightly warmer or more saturated blue compared to Peruvian opal, and it's less common in the commercial market. Oregon mining is similarly small-scale and hand-sorted. For our secondary source, documentation of labor practices and environmental oversight is less robust than we prefer, and we continue working to deepen that sourcing relationship.

Authentication and testing

Genuine blue opal is softer than quartz but will not scratch under fingernail or copper coin pressure. Opalite, the glass substitute, has about the same hardness, so scratching will not tell them apart. Opalite shows a very even color without the natural color variation of genuine opal. Dyed chalcedony, another market substitute, is harder than opal and usually shows more intense, obviously artificial color.

Genuine blue opal is translucent when held to light, showing a subtle glow. Opalite is translucent too, but its glow is very even: blue against a dark background and milky orange or pink against a light one. True opal also has a waxy feel, not a cold glassy feel. An acid test will not help: opal is silica and does not fizz in vinegar.

Pricing and market notes

Tumbled blue opal sits at the entry level, and price rises with size and polish quality. Hand-polished pieces and raw chunks cost a little more, and larger specimens, special forms, or pieces selected for exceptional color command a premium. Price alone will not separate genuine opal from opalite; the tells are opalite's very even color, its blue or orange glow against dark and light backgrounds, and its cold, glassy feel, as described above.

Warning signs: blue opal sold without origin disclosure, material claimed to be "museum quality" or "rare" when blue opal is commercially available, and pieces showing zero color variation or translucence despite claims of natural status. Reputable sellers can discuss their sourcing relationship and testing methods without defensiveness.