The facts
What onyx actually is
The species behind onyx is chalcedony (banded) / calcite (architectural), SiO₂ or CaCO₃; it forms in the trigonal system.
Iron and manganese in banding; architectural "onyx" is banded calcite, a different material entirely is responsible for the colour — and the chromophore, not the name, is what decides whether a colour is stable.
On the instruments it reads a refractive index of 1.530–1.540 or 1.486–1.658 and a specific gravity of about 2.58–2.64 or 2.71, with none in chalcedony; perfect rhombohedral in calcite cleavage.
Where onyx comes from
Commercial material comes from Puebla, Mexico, Iran, Pakistan, Turkey and Brazil.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How onyx is treated
Black onyx is almost always dyed chalcedony. This is a centuries-old accepted practice, not a fraud — but it is a treatment.
We state the treatment on every stone, including when the honest answer is that it cannot be determined. A treatment disclosed is a fact; a treatment discovered later is a refund.
What onyx is confused with
Watch for Dyed chalcedony, Obsidian, Black spinel and Glass — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.530–1.540 or 1.486–1.658 and specific gravity 2.58–2.64 or 2.71 settle most of it in a minute, and magnification settles the rest.
What onyx is used for
The trades that buy onyx are jewellery, architecture and interiors, lighting, furniture, prayer beads, awards and corporate gifts and memorials. They do not want the same thing, and they do not pay in the same unit.
We quote each application in the unit that trade actually buys in, by the carat, by the square metre or by the panel.
Durability and care
Onyx is 6.5–7 or 3–4 on the Mohs scale, with none in chalcedony; perfect rhombohedral in calcite cleavage.
Hardness is not the whole story. Perfect cleavage means the stone can split cleanly if struck along the wrong plane, whatever its Mohs number, so a protective setting matters more here than the hardness suggests.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What onyx costs
Expect roughly $0.50–10/ct; slabs $80–600/m², depending on quality.
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 onyx treated, and how?
Black onyx is almost always dyed chalcedony. This is a centuries-old accepted practice, not a fraud — but it is a treatment.
Where does onyx come from?
Puebla, Mexico, Iran, Pakistan, Turkey and Brazil. Origin affects price, so we name the locality rather than the country on every quote.
Is onyx hard enough to wear every day?
With care. It is 6.5–7 or 3–4 on the Mohs scale, which is hard enough, but none in chalcedony; perfect rhombohedral in calcite cleavage means it can split if struck at the wrong angle. Use a protective setting and avoid ultrasonic cleaning.
How much does onyx cost?
Indicatively $0.50–10/ct; slabs $80–600/m². 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 onyx confused with?
Most often Dyed chalcedony, Obsidian, Black spinel and Glass. A refractive index of 1.530–1.540 or 1.486–1.658 and a specific gravity near 2.58–2.64 or 2.71 separate it quickly.
What is onyx used for besides jewellery?
architecture and interiors, lighting, furniture, prayer beads, awards and corporate gifts and memorials. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for onyx?
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 onyx