The oldest known findings of red coral date from the Mesopotamia civilization, i.e. from about 3000BC. For centuries, this was the coral par excellence, and at the time of Pliny the Elder it was apparently much appreciated in India, even more than in Europe. The name is derived from the Latin corallium, related to the Greek korallion.



Appearance:
The red coral from the Mediterranean (Corallium rub rum) has very faint concentric rings. It is easier to see the longitudinal structures. The type from the seas near Japan has more clearly visible organic structures. The thin branches were and still are polished, pierced, and threaded, unaltered, into necklace. Larger pieces are cut en spherical or faceted necklace beads, pear shape or pendent jewellery, or cabochons. This coral is very compact and easily acquires a good polish, although this may deteriorate in time as the material is not very durable. It is also used for carved pieces and small figurines, in both oriental and western art styles.

The most highly priced varieties of coral are those that of a uniform, strong, brighter. Specimens that are too light or too dark, or have an orange tinge or unevenly distributed color, are less valuable. Some basically red Japanese corals have a white axial portion. This is, of course regarded as a defect, where is not eliminated in the cutting process.



Distinctive features:
Two basic facts must be remembered in distinguishing corals from its imitations: the specimen should have the organic structure characteristic of coral; on contact with the drop of hydrochloric acid(the readily available muriatic acid), the piece should display the strong effervescence characteristic of calcite. The most frequent imitation is of glass. These have longitudinal striation similar to those of coral, but do not react to hydrochloric acid. Another common stimulant is made from a compact, artificial agglomerate mainly of calcite, which lacks any trace of organic structure. As mentioned, the hardness is about 3.5, therefore well below that of glass. The organic substance in coral also gives it very good tenacity, far superior to that of the constituent mineral alone. Because of its organic content, the density varies quite widely but is usually about 2.60-2.66 g/cm3



Occurrence:
Red coral is gathered in the Mediterranean (mainly near Sardinia and Sicily), the eastern Mediterranean, the red sea, and the seas around Japan.



Value:
When made into polished and / or faceted necklace beads, it has roughly the same value as that of certain priced ornamental stones, such as good quality turquoise and lapis lazuli, the color, homogeneity of each piece(individually and as part of the necklace) and polish are very important. When the coral is made into carved pieces and figurines, the quality of work is obviously very important. Furthermore, it should be remembered that large pieces are hard to find.



Simulants and Synthetics:
Very small pieces of coral or branching twigs are imitated by special glass which simulates the typical longitudinal structures; but clearly fused surfaces, the presence of air bubbles, and immunity to attack from hydrochloric acid uncover these imitations quite easily, especially if they are viewed through a lens or binocular microscope. Nowadays coral/colored agglomerate consisting mainly of calcite and called synthetic coral is also manufactured.