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Coral

Unlike most other gemstones which are of mineral origin, Coral is organic, formed by living organisms. It forms from branching, antler-like structures created from coral polyps in tropical and subtropical ocean waters. When the coral polyps die, the hardened skeleton remains, and this material is what is used as a gemstone. Most coral is white, but nature can create coral in several other colors, including the popular orange to red forms. This Red Coral, or Precious Coral as it is often known by, is the most used gemstone form of Coral. In fact, the color known as coral is derived from the typical pinkish-orange color of many red Coral gemstones.

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 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.

Sources:

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.

Similar Gemstones:

Red Coral may be confused with Carnelian, which is much harder. White Coral may be confused with Ivory.