Red coral, also called precious coral, is the hard skeleton of small colonial sea animals in the genus Corallium and related genera. It ranges from deep red through orange and pink to white. The Mediterranean species, Corallium rubrum, has been carved into beads and ornaments since ancient times, and the town of Torre del Greco near Naples is the best-known center for coral carving. Some corals are subject to trade rules, and dyed and imitation coral is common.
What precious coral is
Coral colonies are made of many tiny animals called polyps. Each polyp builds a hard skeleton beneath itself, and over time the colony grows into a branching, tree-like shape. Precious coral differs from the reef-building corals of shallow tropical seas. It grows slowly, often in deeper water, and its skeleton is a solid, fine-grained material that takes a good polish.
The skeleton is made of calcite, a form of calcium carbonate, with a small amount of organic matter. Red and pink colors come from carotenoid pigments. Polished coral shows fine parallel lines along the length of each branch, and cross-sections often show faint concentric rings and a wavy, radial pattern. This structure helps separate natural coral from imitations.
Coral is one of the organic gems, produced by living animals. It is soft, about 3 to 4 on the Mohs hardness scale, and sensitive to acids.
Sources and species
The Mediterranean red coral, Corallium rubrum, grows on rocky seabeds and in caves along the coasts of Italy, France, Spain, Tunisia, Algeria and other Mediterranean countries. It also occurs in nearby Atlantic waters. Branches are usually small, and the color ranges from orange-red to deep red.
Several Pacific species grow in deeper water near Japan, Taiwan and the Midway area. Trade names describe the colors:
- Aka: deep red coral from Japanese waters, often with a white center.
- Momo: pink to orange-pink coral.
- Angel skin: pale pink coral with an even, soft color.
- White coral: also used in jewelry, though less valued.
Pacific coral branches can be much larger than Mediterranean coral, which allows bigger beads and carvings.
History and Torre del Greco
Mediterranean coral appears in jewelry and amulets from the ancient world. Romans prized it, and coral was traded east to India and beyond, where it was valued highly. In Europe, coral was carved into beads and amulets and was often given to children. These protective uses rest on folk belief, not established fact.
Torre del Greco, on the Bay of Naples, has been a center for coral fishing and carving for centuries. In the 19th century the town developed a large coral industry, with workshops turning out cameos, carved beads, figures and jewelry. Torre del Greco carvers also work shell cameos, and the town is still known for both. Coral was also popular in Victorian jewelry, and the page on Victorian jewelry describes that period.
Coral has long been important in other traditions too. It appears in Tibetan and Himalayan jewelry, Native American jewelry of the Southwest, and as one of the nine gems in the Indian navaratna arrangement, covered on the page about jewelry of India.
Harvesting
In the past, coral was dragged from the seabed with weighted nets or crosses, a method that damaged coral beds and has been banned in many places. Today, Mediterranean coral is mostly collected by divers working in deep water, and Pacific coral by submersibles or other gear under national rules. Precious coral grows slowly, often less than a millimeter in diameter per year, so overharvested beds take a long time to recover.
Trade rules and conservation
Because precious coral grows slowly, its harvest is regulated in many countries through permits, size limits, closed areas and quotas. Several Corallium species found in Chinese waters are listed on Appendix III of CITES at China's request, which means international trade in those species needs documentation. Black coral and the stony reef-building corals are listed on Appendix II.
Proposals to list more precious coral species on Appendix II have been debated at CITES meetings. Rules differ by country and change over time. Anyone buying or traveling with coral, especially antique pieces or pieces of unclear origin, should check the current rules in each country involved.
Dyed coral and imitations
Because fine red coral is costly, many materials imitate it.
- Dyed bamboo coral: bamboo coral, from the family Isididae, has white calcareous segments joined by dark organic nodes. It is often dyed red and sold as coral. Its color may look uneven, and dye can gather in cracks.
- Dyed pale coral: lighter natural coral is sometimes dyed to deepen its color.
- Filled or coated coral: porous coral may be filled with resin or coated to improve its surface.
- Reconstituted coral: coral powder bound with resin.
- Glass, plastic and dyed shell or bone: all have been used as imitations.
- Gilson coral: an imitation material made from calcite and pigment.
A cotton swab dampened with acetone can pick up dye from some dyed coral, but this test can damage treated pieces and is not conclusive. A gem lab can identify dyes and imitations using magnification and spectroscopy. The page on gemstone treatments covers dyeing and filling, and the page on identifying gemstones explains when to use a lab.
Care
Coral is soft, porous and sensitive to acids, heat and chemicals. Perfume, hairspray, lotions and cleaning products can dull or etch it. Put coral jewelry on last and wipe it with a soft, damp cloth after wear. Avoid ultrasonic and steam cleaners. Strong light and heat may fade some coral over time. Store it apart from harder gems. The guide to cleaning jewelry safely covers coral and other organic materials such as pearls.
Frequently asked questions
What is precious coral made of?
It is made of calcite, a form of calcium carbonate, with a small amount of organic matter. Carotenoid pigments give red and pink coral their color.
Where does red coral come from?
The classic red coral, Corallium rubrum, comes from the Mediterranean Sea. Other precious corals come from deep Pacific waters near Japan and Taiwan.
How can you spot dyed coral?
Dyed coral may show color gathered in cracks or uneven color, and dyed bamboo coral shows segmented joints. A gem lab can confirm dye and imitations.
Is it legal to buy coral jewelry?
Rules depend on the species and on the countries involved. Some species are listed by CITES, and many countries regulate harvest, so check the current rules before buying or traveling.