The facts
What precious Opal actually is
Mineralogically, precious Opal is opal — SiO₂·nH₂O, crystallising in the amorphous system.
The colour is caused by body colour near-colourless to milky; play-of-colour is diffraction from an ordered array of silica spheres. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.37–1.47 (usually 1.44–1.46), and the specific gravity sits near 1.98–2.25; cleavage is none (conchoidal fracture).
Where precious Opal comes from
The recognised sources are Coober Pedy, South Australia, Mintabie, South Australia and White Cliffs, New South Wales, Australia.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How precious Opal is treated
Australian sedimentary opal is normally untreated. Doublets and triplets (thin opal on a dark backing, sometimes with a quartz cap) are legitimate but must be disclosed. Sugar/smoke treatments are applied to some material to darken the base. Crazing is a stability risk, not a treatment.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What precious Opal is confused with
The usual confusions are Opal doublets and triplets, Synthetic (Gilson) opal, Opalescent glass and resin and Slocum stone.
The separation is rarely a matter of opinion: refractive index 1.37–1.47 (usually 1.44–1.46) and specific gravity 1.98–2.25 settle most of it in a minute, and magnification settles the rest.
What precious Opal is used for
Precious Opal is bought by jewellery, mineral collecting and decorative objects — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the carat, by the specimen or by the piece.
Durability and care
Hardness 5–6.5; cleavage none (conchoidal fracture). That combination decides what it can safely be set into.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What precious Opal costs
Indicative pricing for precious Opal is $10–500/ct depending on play-of-colour.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is precious Opal treated, and how?
Australian sedimentary opal is normally untreated. Doublets and triplets (thin opal on a dark backing, sometimes with a quartz cap) are legitimate but must be disclosed. Sugar/smoke treatments are applied to some material to darken the base. Crazing is a stability risk, not a treatment.
Where does precious Opal come from?
Coober Pedy, South Australia, Mintabie, South Australia and White Cliffs, New South Wales, Australia. Origin affects price, so we name the locality rather than the country on every quote.
Is precious Opal hard enough to wear every day?
Not really. At 5–6.5 on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does precious Opal cost?
Indicatively $10–500/ct depending on play-of-colour. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is precious Opal confused with?
Most often Opal doublets and triplets, Synthetic (Gilson) opal, Opalescent glass and resin and Slocum stone. A refractive index of 1.37–1.47 (usually 1.44–1.46) and a specific gravity near 1.98–2.25 separate it quickly.
What is precious Opal used for besides jewellery?
mineral collecting and decorative objects. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for precious opal?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about precious opal