The facts
What black opal actually is
Black opal is classified as hydrated silica, with the composition SiO₂·nH₂O. It crystallises in the amorphous system.
Colour comes from diffraction over a dark body tone, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.37–1.52. Specific gravity around 1.98–2.25. Cleavage: none. Those three numbers separate it from most of what imitates it.
Where black opal comes from
Black opal is produced at Lightning Ridge, New South Wales, Australia.
That is the whole list. A single source makes supply fragile and makes any claim of a second origin worth questioning.
How black opal is treated
Smoke and sugar treatment darken lesser material. Doublets are common.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What black opal is confused with
In the trade black opal is most often mistaken for, or substituted by, Treated opal, Doublets or Synthetic opal.
The separation is rarely a matter of opinion: refractive index 1.37–1.52 and specific gravity 1.98–2.25 settle most of it in a minute, and magnification settles the rest.
What black opal is used for
Demand for black 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
Black 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 black opal costs
As a guide, black opal trades around $100–20,000/ct.
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 black opal treated, and how?
Smoke and sugar treatment darken lesser material. Doublets are common.
Where does black opal come from?
Lightning Ridge, New South Wales, Australia. That is the only commercial source.
Is black 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 black opal cost?
Indicatively $100–20,000/ct. 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 black opal confused with?
Most often Treated opal, Doublets and Synthetic opal. A refractive index of 1.37–1.52 and a specific gravity near 1.98–2.25 separate it quickly.
Related stones
Looking for black 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 black opal