The true origin of coral was a source of speculation for many centuries. Theophrastus, Dioscorides, and Pliny all considered that it was a plant, and it was not until the Eighteenth Century that Reaumur and Peyssoull proved that coral was nothing mote than an aggregation of animal matter and the calcareous, skeleton like deposit of a polyp.
Some carving in coral is still done, but very little is really fine work. The best specimens are in old works, for the demand today is mostly for quantity and not quality. The Chinese carve coral, as do the Italians; it is said that the Italian royal family possesses a carved coral handle of a sunshade which was once valued at $1,000 (£360.) Large beads are unusual; a diamond jewelry necklace shown at the International Fisheries Exhibition held at Berlin in 1880 was valued at $16,800 (£6,000). But “chip” coral necklaces may be bought for a few pence, despite that each piece must be drilled by hand, even if no shaping is necessary. Old corals may be recognized by their dull and scratched surfaces; stained coral which has faded often leaves a stain of a deeper color in surface cracks.
A bluish coral which was found off the West African coast and which was occasionally marketed is now seldom seen. It is highly prized by the natives, who wear it in the form of necklaces. It is distinguished by a slightly superior hardness to the ordinary coral, being about 3 1/2 to  3 3/4 on Mohs’ scale.
A black coral, fished in the Indian Ocean, is not really a true coral, being of a horny nature. Its shining black color appeals to the local natives, who call it akabar, and they use it in the form of bracelets and head ornaments. This material is also found in  the  Mediterranean, and it is called giojetto.
The distinction between natural coral and its imitations is generally obvious. Color and hardness are generally sufficient tests, but the application of any acid, which will cause a visible effervescence with coral, is absent with almost all its substitutes. Probably the best imitation is a dyed gypsum, which is very similar in color but heavier and colder to the touch than coral. It may Also be scratched with a fingernail, and it does not effervesce when touched by an acid.