Corals are marine invertebrates typically living in compact colonies of many identical individual "polyps." The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.

Corals can be major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not have associated algae and can live in much deeper water. They live on the Darwin Mounds, north-west of Cape Wrath, Scotland. Corals have also been found off the coast of the U.S. in Washington State and the Aleutian Islands in Alaska.

Used for adornment since prehistoric times, coral inlays and ornaments have been found in Celtic tombs from the Iron Age. An organic gemstone from the sea, coral was believed to bestow wisdom, protect from evil, heal wounds and calm the soul.

White is the most common color in coral, but a variety of other shades can be found, including pink, orange, red and black. The rarest color is a deep red.

Coral is commonly enhanced to improve its color and durability. White coral is bleached. Pink coral is permeated with a colorless wax and orange coral is stabilized with plastic. Black coral is sometimes bleached to create gold coral. Occasionally, red coral is dyed to deepen or uniform its color. All commonly used forms of coral enhancement are stable.

Special care is required for coral regardless of whether or not it is enhanced. A soft and porous gemstone, coral scratches and abrades easily and chlorine, alcohol, ammonia, nail polish remover and other chemicals can damage it.

Here is a photo of a silver ring with Momo coral and Madeira citrine:

Check out more jewelry with coral.