Guam Territorial Gemstone
Coral, like pearl, is of organic origin, a product of marine invertebrates, and composed of more than 90 percent calcium carbonate. The species of coral that is used as a gemstone is calledcorallium rubrum, commonly known as precious coral or red coral. However, corals are not always red, pink, or salmon in color; they grow in a wide range of colors from red to white, blue, and even black.
A TERRITORY SYMBOL
The northern part of Guam is a forested coralline limestone plateau, and a coral reef surrounds most of the island. Human activity, such as urban development and unregulated use of off-road vehicles, as well as natural occurrences like typhoons and wildfires, have greatly affected Guam’s coral. Several coral reef conservation projects aim to protect this precious natural resource. Coral is an excellent representative of the island’s geography, geology, wildlife, and culture.
The word coral may come from the Greek κορáλλιον (korallion), which denotes the hard, calcareous skeleton of the coral animals, or from an ancient Greek word pronounced kura-halos, meaning "mermaid," since the fine branches of the coral sometimes look like small figures. Alternatively, the word may be derived from the Hebrew גורל (goral), meaning lot or destiny, originally referring to objects used in the drawing of lots. Coral branches may well have been used in this way, since they were once used in oracles in Palestine, Asia Minor, and around the Mediterranean.
FORMATION AND OCCURRENCE
Coral is created from a protein secreted from tiny, cylindrical, underwater polyps that have tentacles and stinging cells. Corals live in colonies up to 6 feet (1.8 m) high. They grow into branches up to a height of 16 inches (40 cm), which are harvested by divers. Coral colonies create a habitat for crustaceans, bivalves, and fish.
Corals grow all over the world at all depths, but the finest quality specimens are usually found in warmer waters. In Hawaii, they grow at depths of about 100–300 feet (30–91 m), shallow enough to harvest using scuba equipment. Many harvesters, however, have died in pursuit of coral trees at the deep end of this range.
For centuries, coral has been harvested for a variety of uses, including idols, beads, cameos, medicine, and talismans.
Coral is often full of holes and cracks, but rare, high-quality coral is of an even color and lacks holes, cracks, blotches, and striations. Red coral, sometimes called fire coral, is the rarest and most valuable. The intense pink or red color of this species make it prized as a gem. To be used in jewelry, coral branches are cleaned, sorted, cut or filed, and polished from their natural matte finish to a high luster. It can take a few years for coral to grow large enough to be used in jewelry.
The Romans believed coral had the power to protect children and heal wounds. In many cultures, coral is still worn to protect the wearer from evil spirits. The mineral is said to relieve tension, decrease fear, and improve one’s social life. Hawaiians traditionally ground black coral into a powder for medicinal purposes.
Artificial coral is made of glass, plastic, and porcelain.
Crystal Structure: trigonal
Hardness (Mohs): 3-4
Color: Multiple colors, commonly white, red and black
Refractive Index: 1.486-1.658
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press