For centuries, coral-- like pearl, a gift of the sea-- was classed among the precious gems valued by man. Not strictly a mineral, coral is an organic substance, composed of the skeletons of millions of tiny marine animals. In its natural state, coral is plantlike in appearance and grows in warm water at depths of up to ninety feet. It must be harvested live to retain its color. Though white coral is quite common, and forms the great reefs of the world, the rarer hues of red, orange, pink and black are much sought after as jewelry and amulets. Pink coral is particularly flattering to the complexion of the wearer and is called "angel skin". According to ancient sources, Assyrian glassmakers creating opaque colored glass in imitation of precious gems, were trying -to form red glass to resemble coral, rather than ruby. Examples of coral set in precious metals are known from the Biblical, Egyptian and Classical cultures, and its popularity has continued unbroken through the ages. The native jewelry of the Arabian peninsula makes excellent use of bright corals combined with silver. The therapeutic effects of coral have long been understood: it is used as a heart stimulant, an antidote for fevers and toxins in the system, a cure for colic and vomiting and a prevention for childhood diseases. In addition, it is believed to avert sterility. As with the pearl, coral's mysterious strength seems to derive from its organic source material, the accumulated energy of living things.