The facts
What sponge Coral actually is
Sponge Coral is classified as porous calcareous skeleton of melithaeid gorgonians and similar reef corals, with the composition Calcite / aragonite CaCO3 with organic matrix. It crystallises in the aggregate system.
Colour comes from weak natural carotenoids; commercial colour is dye, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.486-1.658. Specific gravity around 2.3-2.7 (lower where porous or resin-filled). Cleavage: none; visibly porous, spongy texture. Those three numbers separate it from most of what imitates it.
Where sponge Coral comes from
Sponge Coral is produced at Taiwan and the South China Sea, Indonesia and the Philippines and Mediterranean (historic).
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 sponge Coral is treated
Almost always dyed and resin- or wax-impregnated to fill the porosity; the pore structure is visible at 10x and is the giveaway. Not CITES-listed as a group, but reef Scleractinia are on Appendix II, so material harvested from stony reef corals does require permits - vendors are often vague about which organism it came from. Sold constantly as 'coral' without qualification.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What sponge Coral is confused with
In the trade sponge Coral is most often mistaken for, or substituted by, Precious coral, Bamboo coral or Dyed and stabilised turquoise-style composites.
The separation is rarely a matter of opinion: refractive index 1.486-1.658 and specific gravity 2.3-2.7 (lower where porous or resin-filled) settle most of it in a minute, and magnification settles the rest.
What sponge Coral is used for
Demand for sponge Coral comes from jewellery and decorative objects, 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 piece.
Durability and care
Sponge Coral is 3-4 on the Mohs scale, with none; visibly porous, spongy texture 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 sponge Coral costs
As a guide, sponge Coral trades around $0.10-3 per gram.
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 sponge Coral treated, and how?
Almost always dyed and resin- or wax-impregnated to fill the porosity; the pore structure is visible at 10x and is the giveaway. Not CITES-listed as a group, but reef Scleractinia are on Appendix II, so material harvested from stony reef corals does require permits - vendors are often vague about which organism it came from. Sold constantly as 'coral' without qualification.
Where does sponge Coral come from?
Taiwan and the South China Sea, Indonesia and the Philippines and Mediterranean (historic). Origin affects price, so we name the locality rather than the country on every quote.
Is sponge Coral hard enough to wear every day?
Not really. At 3-4 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 sponge Coral cost?
Indicatively $0.10-3 per gram. 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 sponge Coral confused with?
Most often Precious coral, Bamboo coral and Dyed and stabilised turquoise-style composites. A refractive index of 1.486-1.658 and a specific gravity near 2.3-2.7 (lower where porous or resin-filled) separate it quickly.
Related stones
Looking for sponge coral?
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 sponge coral