Chemical Formula Mostly calcium carbonate
Color White, Red, Orange, Pink, Gray, Black
Hardness 3 – 4
Crystal System Amorphous
Refractive Index 1.48 – 1.65
SG 2.6 – 2.7
Transparency Translucent to opaque
Double Refraction -.172
Luster Vitreous, waxy
Cleavage None

Coral is an ancient gemstone, and has been used for thousands of years. Aside from the lovely solid colors found in Coral, it can also have color zones or swirls, with white, pink, orange, and red being the most prevalent. Coral is naturally dull; polishing is required to bring out its glassy luster. Coral gemstones can be either solid or porous, depending on the polyp formation. Despite Coral’s pretty colors, it is very soft and brittle, and does not make a durable gemstone. It is prone to both scratches and chipping. Due to environmental protection laws worldwide, production of Coral for the gemstone trade is on the decline.


Coral is used as cabochons and beads. It is also sculpted into small carvings such as flowers for pins and brooches. Small branches of Coral are sometimes stranded into spiky, dangling necklaces.


Black Coral – Marine coral species of the antipatharia family with a black color.
Precious Coral – Also known as Red Coral, describes the marine coral species corallium rubrum (or several related species of marine coral). Precious coral has a natural pink to red color and is the most desirable jewelry form of Coral.
Red Coral – Marine coral species corallium rubrum (or several related species) with a naturally colored light pink to deep red color.Most gemstone Coral is natural, but caution should be taken as some Coral, especially with a deep red color, may be dyed.Coral is found only in tropical to subtropical saltwater environments. Regions producing coral include the Red Sea, the Midway Islands, the Canary Islands, the Taiwan and Malaysian Coast, the coast of Australia, Italy, (Sardinia), and Hawaii.Red Coral may be confused with Carnelian, which is much harder. White Coral may be confused with Ivory.
Danburite is primarily a collectors gemstone. It is usually colorless; yellow and light pink gems are seldom cut. Danburite is named after the city of Danbury, Connecticut, where this mineral was first described, though no gem grade material has come from Danbury. Danburite has good hardness and facets well, but its lack of fire in colorless stones limits its use as a mainstream gemstone.

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