Coral is the external skeleton of a tiny, plant-like marine animal called the coral polyp. The structures that result from generations of these creatures growing as colonies on top of each other can be quite massive. Since time immemorial, coral has been used for carvings, cabochons, and other jewelry pieces.
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Top values for calcareous coral go to red, pink, and orange pieces. Other colors are graded separately. Highest values for conchiolin coral go to black, then brown. Gold color has additional value, especially if it shows a sheen. When polished, the color may shimmer through a transparent layer.
Coral growths come in many shapes. The coral commonly used to make gems is branched and treelike. The largest sections of a coral’s trunk are used for carvings, which can be quite valuable. The determining value factors are the size and color of the piece as well as the skill of the artist.
This Nigerian bead work is called “Coral Highness,” since the necklace combines red corals, marble stones, and a gold pendant, and it’s also very suitable for a lady of royal lineage. Photo and description by Benita Nnachortam. Licensed under CC By-SA 4.0.
The gem use of coral began before recorded history. The Ancient Greeks, Romans, and Native Americans used red, pink, and white corals extensively. Deep red, bright pink, and clear white corals were highly prized. Inland cultures far from the undersea sources of coral would trade for these objects.
Tibetan tobacco pouch made from leather, silver, bronze, coral, and turquoises. Photo by Vassil. Public Domain.
Although relative newcomers to the cultures of the Northern Hemisphere, black and gold coral have a long history of use as gem material in their native territories, primarily off the coasts of Hawaii and Cameroon. Akori corals from Cameroon were highly prized before the 18th century.
The rarest gem coral variety, Hawaiian gold coral is also harder than other varieties. It was first described scientifically in the 1970s. The harvesting of this gem material, however, is currently restricted and cost prohibitive due to environmental considerations.
The best red corals come from the Mediterranean. Italy works most of the Mediterranean corals, but Hong Kong also receives a great deal of this material for cutting. Conversely, Italy is also a major buyer of Taiwanese material.
China and Taiwan cut large quantities of white, pink, mottled, and ox-blood corals from the South China Sea.
Calcareous corals: composed primarily of calcite and come in whites, reds, and pinks.
Conchiolin corals: composed of conchiolin, the same substance found in pearls and other shells, and come in black, brown, and gold colors.
The conchiolin type is tougher and less brittle than the calcareous type.
A close relative of conchiolin corals is the rare blue coral. The hues are very nice, but the saturation is low, so these pieces tend towards gray shades.
Calcareous corals have wavy, fibrous structure, cavities from polyps, and high spot birefringence.
Conchiolin corals have a concentric, circular growth pattern (“tree rings”) and show white crescents in cross sections of branches.
In the 1970s, Pierre Gilson developed “created corals” to help protect the natural variety from destructive harvesting. This imitation red and pink coral has a specific gravity (SG) of 2.44. This is always lower than natural red and pink material. This synthetic has weak birefringence and lacks natural structure. Under high magnification, you can see a fine granular texture.
Although dyeing can improve or even change a piece’s color, the new color may fade. This process can be identified by magnification or a solvent test. The addition of dyes may produce phosphorescence.
Bleaching produces gold coral from black. This is a stable treatment. This process can be identified by magnification (which reveals a different texture) and lower SG and refractive index values.
The Mediterranean and Red Sea areas are the principal producers of gem-quality coral. Although more commonly found in tropical regions, in shallow waters with a temperature from 13-16°C, coral reefs can also occur in colder, deeper waters, such as those found to the west of Ireland.
Other notable producers include the ocean waters off the following areas:
Australia; Cameroon; Hawaii; Japan; Malaysia; Mauritius; South Africa; Spain; Taiwan.
The corals used to make jewelry were once the exoskeletons and homes of living creatures, coral polyps, that come out at night. Photo by Derek Keats. Licensed under CC By 2.0.
Branches may be several inches to several feet long but aren’t always thick.
Coral Trade Names
Akori, from Cameroon
Algerian, low quality
African Star, from South Africa, red, pink, violet and yellow/orange
Angel skin, light pink
Arciscuro, darkest red
Carbonetto, darkest red
Italian, good quality, white or pink
Japanese, pink with white center
Moro, high quality, light purplish red Japanese coral
Tosa, average quality Japanese coral
Ox blood, dark red
Pelle d’angelo, light pink
Rosa pallido, light pink
Rosa vivo, medium pink
Rosso scuro, dark red
Salmon, light pink
Sardinian, high quality, very hard
Sicilian, low quality
Black, black to dark brown
Blue, light to medium dark blue
Gold, yellow to brownish yellow, may have sheen
Corals are sensitive to heat and should be cleaned only with a damp cloth and dried carefully. Mechanical cleaning methods, such as ultrasonic, aren’t recommended. Consult our gemstone jewelry cleaning guide for more recommendations.