The facts
What matrix Opal actually is
Matrix Opal is classified as precious opal within a porous host rock, with the composition SiO₂·nH₂O in ironstone or porous sandstone. It crystallises in the amorphous in a rock matrix system.
Colour comes from play-of-colour from ordered silica spheres; the black background is carbon or iron deposited in the host, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.44–1.47. Specific gravity around 2.0–2.5. Cleavage: none. Those three numbers separate it from most of what imitates it.
Where matrix Opal comes from
Matrix Opal is produced at Andamooka, South Australia, Yowah, Queensland, Australia and Wello, Ethiopia.
The locality is part of the description, not a footnote — two stones of the same weight from two of these places are not the same stone.
How matrix Opal is treated
Andamooka matrix opal is almost always treated: soaked in sugar solution then boiled in sulphuric acid to deposit carbon in the pores, or smoke-treated. This is an accepted trade practice but must be disclosed — untreated matrix opal is pale and far less valuable, and the treatment is permanent.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What matrix Opal is confused with
In the trade matrix Opal is most often mistaken for, or substituted by, Black opal, Boulder opal or Doublets and triplets.
The separation is rarely a matter of opinion: refractive index 1.44–1.47 and specific gravity 2.0–2.5 settle most of it in a minute, and magnification settles the rest.
What matrix Opal is used for
Demand for matrix Opal comes from jewellery and mineral collecting, which is why one price per carat never covers it.
We quote each application in the unit that trade actually buys in, by the carat or by the specimen.
Durability and care
Matrix Opal is 5.5–6.5 on the Mohs scale, with none cleavage.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What matrix Opal costs
As a guide, matrix Opal trades around Treated matrix 10–150 USD/ct; untreated far less.
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 matrix Opal treated, and how?
Andamooka matrix opal is almost always treated: soaked in sugar solution then boiled in sulphuric acid to deposit carbon in the pores, or smoke-treated. This is an accepted trade practice but must be disclosed — untreated matrix opal is pale and far less valuable, and the treatment is permanent.
Where does matrix Opal come from?
Andamooka, South Australia, Yowah, Queensland, Australia and Wello, Ethiopia. Origin affects price, so we name the locality rather than the country on every quote.
Is matrix Opal hard enough to wear every day?
Yes. At 5.5–6.5 on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does matrix Opal cost?
Indicatively Treated matrix 10–150 USD/ct; untreated far less. 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 matrix Opal confused with?
Most often Black opal, Boulder opal and Doublets and triplets. A refractive index of 1.44–1.47 and a specific gravity near 2.0–2.5 separate it quickly.
Related stones
Looking for matrix 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 matrix opal