The group
The trade word "coral" covers animals that are not closely related and materials that are not comparable in value. Mediterranean red coral, Corallium rubrum, is the historic and most valuable one, fished off Sardinia, Sicily, Spain and Tunisia and cut for centuries at Torre del Greco. The Pacific species — aka, momo, shiro — come from Japan and Taiwan.
Black coral is a different order entirely, Antipatharia, and is horn-like protein rather than carbonate. Blue coral, Heliopora, is another. Bamboo coral is cheap, pale and almost always dyed red to imitate the precious species — it is the dominant fake.
The legal position is widely misunderstood and worth getting right. Corallium rubrum is not on CITES Appendix I or II — proposals to list it were defeated. Four Pacific Corallium species are on Appendix III at China's request. Antipatharia, Helioporidae and Tridacnidae are on Appendix II. So some coral moves freely and some needs paperwork, and the species name decides which.
At 3 to 4 on the Mohs scale coral is soft, and being carbonate it is dissolved by acid — including perfume, vinegar and perspiration. It is a material for occasional wear, and it should never go near an ultrasonic cleaner.
Every coral compared
The whole group side by side. Where the constants overlap, the species cannot be named from a refractometer alone — which is exactly why the trade names mislead.
| Variety | Species | Colour | Mohs | RI | SG | Guide price |
|---|---|---|---|---|---|---|
| Agatized Coral | Oligocene-Miocene scleractinian coral colonies in which the aragonite skeleton has been replaced by chalcedony - a fossil, and silica, not carbonate | colourless | 6.5-7 | 1.53-1.54 (spot) | 2.55-2.65 | $1-15 per carat cut; display slabs and heads $30-400 each |
| Aka Coral | Calcareous skeleton of the deep-water octocoral Corallium japonicum | red | 3-4 | 1.486-1.658 | 2.60-2.70 | $500-5,000 per gram for fine undyed oxblood; top Japanese cabochons exceed $10,000 per gram |
| Angel Skin Coral | The pale, evenly-coloured pink to near-white grade of Pleurocorallium elatius and related species | pink | 3-4 | 1.486-1.658 | 2.60-2.70 | $200-2,000 per gram for genuine even-toned undyed material |
| Aragonite | Aragonite | colourless | 3.5–4 | 1.530–1.685 | 2.94 | Specimens $10–$800; fine Austrian flos ferri $200–$3,000 |
| Bamboo Coral | Calcitic internodes of deep-sea isidid gorgonians, alternating with dark horny nodes - hence the bamboo look | colourless | 3-4 | 1.486-1.658 | 2.60-2.70 | $0.20-5 per gram; sold at Corallium prices when undisclosed |
| Black Coral | Horny proteinaceous skeleton of antipatharian corals - not carbonate at all | black | 2.5-3.5 | 1.56 (spot) | 1.34-1.46 | $5-80 per gram worked; Hawaiian licensed material commands a substantial premium |
| Blue Coral | Aragonitic skeleton of Heliopora coerulea, the only octocoral with a massive aragonite skeleton | blue | 3-4 | 1.53-1.68 (spot around 1.65) | 2.1-2.5 | $5-60 per gram worked |
| Golden Coral | Proteinaceous skeleton of Kulamanamana haumeaae, a zoanthid that overgrows black coral, plus some bleached Antipatharia sold under the same name | yellow | 2.5-3.5 | 1.56 (spot) | 1.34-1.46 | $20-200 per gram for documented natural Hawaiian material |
| Mediterranean Red Coral | Calcareous axial skeleton of the gorgonian octocoral Corallium rubrum | red | 3-4 | 1.486-1.658 (calcite birefringence; spot reading around 1.49-1.65) | 2.60-2.70 | $100-1,500 per gram finished for fine untreated Mediterranean red; branches and rough $50-400 per gram |
| Momo Coral | Calcareous skeleton of the octocoral Pleurocorallium (Corallium) elatius | pink | 3-4 | 1.486-1.658 | 2.60-2.70 | $50-600 per gram finished depending on saturation and size |
| Petoskey Stone | Fossil rugose coral in limestone | colourless | 3.5–4 | Opaque | 2.6–2.8 | Tumbled stones 5–30 USD; large polished pieces 50–400 USD |
| Sponge Coral | Porous calcareous skeleton of melithaeid gorgonians and similar reef corals | red | 3-4 | 1.486-1.658 | 2.3-2.7 (lower where porous or resin-filled) | $0.10-3 per gram |
| White Precious Coral | Calcareous skeleton of the white precious coral Pleurocorallium (Corallium) konojoi | colourless | 3-4 | 1.486-1.658 | 2.60-2.70 | $3-40 per gram undyed |
Questions
Is red coral CITES protected?
It depends on the species, and the trade routinely gets this wrong. Mediterranean Corallium rubrum is not on CITES Appendix I or II — listing proposals were defeated. Four Pacific Corallium species are on Appendix III. Black coral (Antipatharia) and blue coral (Helioporidae) are on Appendix II and do need permits.
How do I know if coral is dyed?
Most cheap red coral is dyed bamboo coral. Dye concentrates in fissures and in the porous growth rings, and an acetone swab often lifts colour. Natural precious coral shows fine concentric and radial structure under magnification that dyed bamboo coral does not.
What is reconstituted coral?
Coral powder or fragments bound with resin and pressed into shape. It is sold as coral and is legally a manufactured product, not a gem. It is usually detectable by its uniform texture and the absence of natural growth structure.
Can I wear coral every day?
Not really. At 3 to 4 on the Mohs scale it scratches easily, and as a carbonate it is attacked by acids — perfume, perspiration and household cleaners all damage it. Wear it occasionally, put it on last, and never clean it ultrasonically.
Looking for coral?
Tell us which variety, what size and what it is for. We source it, photograph it and quote it, with the locality named.
Ask about coral