No faceted gemstone produces play-of-colour. Opal does not refract light — it diffracts it, through a three-dimensional array of silica spheres stacked with extraordinary regularity. The result is spectral colour that moves, shifts, and changes with every degree of rotation. Every opal is unrepeatable.
Opal's colour is structural, not chemical. Inside the stone, spheres of amorphous silica — each between 150 and 300 nanometres in diameter — stack in regular, three-dimensional arrays during formation from silica-rich groundwater percolating through rock. When light enters the stone, it diffracts off these arrays at wavelengths that correspond to the sphere size and spacing. Large spheres produce red and orange. Smaller spheres produce blue and violet. A stone with irregular sphere sizes produces the full spectrum simultaneously — the phenomenon known as play-of-colour.
No two opals are identical because no two silica sphere arrays form identically. The pattern, the colour distribution, the directionality of the play — these are unique to each stone. You cannot replicate an opal. You can only find it.
The black opal from Lightning Ridge in New South Wales, Australia, is the most prized opal in the world, and my personal favourite. The "black" refers not to the colour of the play-of-colour — which can include every spectral hue — but to the body tone of the stone: a dark grey to black potch background that makes the spectral colours appear with extraordinary vividness. Against a dark body, red, orange, and violet flash with an intensity that a white or crystal opal cannot match.
Fine Lightning Ridge black opal is genuinely rare material. The Lightning Ridge field is a small area, the mining is artisanal and unpredictable, and stones with strong red play-of-colour across a true black body are among the most expensive coloured stones by weight in existence. A fine black opal with dominant red flash commands prices that rival fine ruby and alexandrite.
What draws me to black opal specifically is that it rewards sustained attention. A casual glance gives you one stone. A minute of looking — moving the stone through different angles, different light sources — gives you dozens of stones. The pattern of colour shifts, new colours appear, directions of flash change. No other gem behaves this way.
Boulder opal forms within ironstone boulders in Queensland, Australia. Thin veins of opal run through the host rock, and cutters often leave the ironstone matrix intact as backing — producing stones with a natural dark body tone similar to black opal, but with the matrix visible as part of the composition. Boulder opal frequently shows strong colour and distinctive patterns, and it is significantly more affordable than Lightning Ridge black opal while sharing much of its visual intensity.
Crystal opal is transparent to semi-transparent with play-of-colour visible through the body. Fine crystal opal can be spectacular — the transparency adds a depth to the colour play that is different from the surface flash of black opal. White opal has a milky or white body tone; the colour play tends to be pastel and softer. Both are primarily from South Australia's Coober Pedy fields.
Opal demands the most careful setting design of any stone I work with. Its hardness (5.5–6.5) is significantly lower than corundum or diamond, making it vulnerable to impact and abrasion. Settings must protect the stone — closed bezels, recessed crowns, or designs that limit the stone's exposure to lateral impact. The water content of opal (3–21%) also means it can craze — develop fine surface cracks — if allowed to dehydrate rapidly, particularly in very dry environments or under sustained heat from jeweller's tools.
For these reasons, opal is not a stone for every client or every application. But for a client who understands the material and wants something genuinely irreplaceable — a stone that will never exist again in exactly the same form — nothing else compares.
Stones whose character goes beyond colour
Fine black opal from Lightning Ridge is among the rarest materials I work with. When I find something exceptional, I bring it home.
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