The facts
What operculum actually is
Mineralogically, operculum is calcareous trapdoor (operculum) of the turban snail Turbo petholatus and related species — Aragonite / calcite CaCO3 with organic matrix, crystallising in the aggregate system.
The colour is caused by natural banded pigment forming the green-brown spiral on the flat face against a white domed face. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.52-1.68, and the specific gravity sits near 2.6-2.9; cleavage is none.
Where operculum comes from
The recognised sources are Philippines and eastern Indonesia, Solomon Islands and Papua New Guinea and Queensland coast, 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 operculum is treated
Normally untreated, sometimes polished and backed. Not CITES. A food-industry by-product, so supply is plentiful and cheap; the main misrepresentation is metaphysical marketing rather than material fraud. Plastic and resin copies exist for the cheap souvenir trade.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What operculum is confused with
The usual confusions are Resin and plastic copies and Shell cabochons.
The separation is rarely a matter of opinion: refractive index 1.52-1.68 and specific gravity 2.6-2.9 settle most of it in a minute, and magnification settles the rest.
What operculum is used for
Operculum is bought by jewellery, decorative objects and mineral collecting — 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 piece or by the specimen.
Durability and care
Operculum is 3.5-4.5 on the Mohs scale, with none cleavage.
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 operculum costs
Indicative pricing for operculum is $0.50-10 each depending on size and pattern.
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 operculum treated, and how?
Normally untreated, sometimes polished and backed. Not CITES. A food-industry by-product, so supply is plentiful and cheap; the main misrepresentation is metaphysical marketing rather than material fraud. Plastic and resin copies exist for the cheap souvenir trade.
Where does operculum come from?
Philippines and eastern Indonesia, Solomon Islands and Papua New Guinea and Queensland coast, Australia. Origin affects price, so we name the locality rather than the country on every quote.
Is operculum hard enough to wear every day?
Not really. At 3.5-4.5 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 operculum cost?
Indicatively $0.50-10 each depending on size and pattern. 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 operculum confused with?
Most often Resin and plastic copies and Shell cabochons. A refractive index of 1.52-1.68 and a specific gravity near 2.6-2.9 separate it quickly.
What is operculum used for besides jewellery?
decorative objects and mineral collecting. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for operculum?
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 operculum