Sponge coral is known scientifically as melithaea ochracea, and despite its name, it is not a sponge at all. Instead, it is a type of coral that has a spongelike appearance. Sponge coral is imported to the United States from Asia, and it is popularly used in jewelry. Sponge coral may be rough or it may be polished smooth into beads or pendents.
Sponge coral is primarily found in the South China Sea, in waters close to Taiwan and stretching south to Indonesia. According to JCK, a jewelry industry website, since sponge coral is not endangered, it may be imported to the United States with an import-export license/federal fish and wildlife permit from the U.S. Department of the Interior's Fish and Wildlife Service.
Sponge coral is formed by polyps that create housings for themselves out of calcium carbonate. In the wild, before processing, sponge coral has a treelike structure, but unlike other coral, it is pocked with holes. These holes result from the fact that the polyps that create sponge coral do not close the coral structure entirely. These openings create the spongelike appearance in this coral.
Good sponge coral has a vibrant orange-red color. The coral often has streaks or tinges of yellow in it, with lower-quality specimens having a brownish tint or larger areas of yellow. While the lower-quality specimens are less valuable, they do have a varied visual appearance that can still be valuable in jewelry. Sponge coral also comes in blue with a gray tinge. Sponge coral is fairly soft. It ranks as a 3.5 on the Mohs hardness scale, which measures a stone's resistance to abrasion.
Due to its softness and its porous nature, sponge coral requires special care. Do not use chemical cleaners on coral and prevent sponge coral jewelry from receiving sharp blows. To clean sponge coral, wipe it down with a damp cloth and allow it to air dry before you put it away. Sponge coral should be stored in cloth bag or in its own box to prevent it from getting scratched by other pieces of jewelry.
According to JCK, about 95 percent of all sponge coral on the market has been stabilized. Because of the pocked structure of sponge coral, it is delicate and inclined to breakage unless it has been treated in some way. Very glossy or sleek specimens of sponge coral have had the pocks filled with a polymer or a resin. Some sponge coral also has to be dyed to enhance the natural color. Natural, untreated sponge coral is always rough.
References and ResourcesJCK Online: Sponge Coral; Gary Roskin; JCK Magazine; July 2004
BJ Bead: How to Care for Coral Jewelry