Precious coral

Precious coral

Habitat

Red corals grow on rocky seabottom with low sedimentation, typically in dark environments–either in the depths or in dark caverns or crevices. The original species, C. rubrum, is found mainly in the Mediterranean Sea. It grows at depths from 10 to 300 m, although the shallower of these habitats have been largely depleted by harvesting. In the underwater caves of Alghero, Sardinia (the “Coral Riviera”) it grows at the depth of 4 m. The same species is also found at Atlantic sites near the Strait of Gibraltar and at the Cape Verde Islands. Other Corallium species are native to the western Pacific, notably around Japan (Corallium japonicum) and Taiwan; these occur at depths of 350 to 1500 m in areas with strong currents.

Anatomy

In common with other Gorgonacea, red corals have the shape of small leafless bushes and grow up to a meter in height. Their valuable skeleton is composed of intermeshed spicules of hard calcium carbonate, colored in shades of red by carotenoid pigments. In living specimens, the skeletal branches are overlaid with soft bright red integument, from which numerous retractable white polyps protrude. The polyps exhibit octameric radial symmetry.

Coral as a gemstone

Polished fragments of fake dyed red bamboo coral

Chinese coral sculpture

Non precious red dyed sponge coral earrings

The hard skeleton of red coral branches is naturally matte, but can be polished to a glassy shine. It exhibits a range of warm reddish pink colors from pale pink to deep red; the word coral is also used to name such colors. Owing to its intense and permanent coloration and glossiness, precious coral skeletons have been harvested since antiquity for decorative use. Coral jewelry has been found in ancient Egyptian and prehistoric European burials, and continues to be made to the present day.

Precious coral has relative density of 3.86 and hardness 3.5 on the Mohs scale. Due to its softness and opacity, coral is usually cut en cabochon, or used to make beads.

History of trade in coral

At the beginning of the Christian era, there was a great trade carried on in coral between the Mediterranean and India, where it was highly esteemed as a substance endowed with mysterious sacred properties. It is remarked by Pliny that, previous to the existence of the Indian demand, the Gauls were in the habit of using it for the ornamentation of their weapons of war and helmets; but in his day, so great was the Eastern demand, that it was very rarely seen even in the regions which produced it. Among the Romans branches of coral were hung around children’s necks to preserve them from danger, and the substance had many medicinal virtues attributed to it. A belief in its potency as a charm continued to be entertained throughout medieval times; and even early in the 20th century in Italy was worn as a preservative from the evil eye, and by females as a cure for sterility.

From the middle ages upwards the securing of the right to the coral fisheries on the African coasts was an object of considerable rivalry among the Mediterranean communities of Europe. Previous to the 16th century they were controlled by the Italian republics. For a short period the Tunisian fisheries were secured by Charles V to Spain; but the monopoly soon fell into the hands of the French, who held the right till the Revolutionary government in 1793 threw the trade open. For a short period (about 1806) the British government controlled the fisheries, but later returned to the hands of the French authorities. Previous to the French Revolution much of the coral trade centred in Marseilles; but since that period, both the procuring of the raw material and the working of it up into the various forms in which it is used became peculiarly Italian industries, centering largely in Naples, Rome and Genoa.

Coral in mythology

The origin of coral is explained in Greek mythology by the story of Perseus. Having petrified Cetus, the sea monster threatening Andromeda, Perseus placed Medusa’s head on the riverbank while he washed his hands. When he recovered her head, he saw that her blood had turned the seaweed (in some variants the reeds) into red coral. Thus, the Greek word for coral is ‘Gorgeia’, as Medusa was one of the three Gorgons.

Poseidon resided in a palace made of coral and gems, and Hephaestus first crafted his work from coral.

The Romans believed coral could protect children from harm, as well as cure wounds made by snakes and scorpions and diagnose diseases by changing colour.

Trivia

The two biogenic precious gemstones, coral and pearl, although drastically different in appearance, are chemically very similar. Both are mostly calcium carbonate deposited by marine invertebrates.

Another unrelated species, the Hawaiian black coral is sometimes used as an ornamental material. Its skeleton is not mineralized, consisting mostly of conchiolin.

In Vedic astrology red coral is associated with the planet Mars.

A branch of red coral figures prominently in the civic coat of arms of the town of Alghero, Italy.

References

^ a b c d “Corallium species”. ARKive. http://www.arkive.org/coral/Coral/corallium_more.html. Retrieved 2007-02-15. 

^ a b c “Gemstones: Coral”. http://www.gemstone.org/gem-by-gem/english/coral.html. Retrieved 2007-02-15. 

^ a b “Red Coral”. Marenostrum. http://marenostrum.org/vidamarina/animalia/invertebrados/cnidarios/corales/rojoi.htm. Retrieved 2007-02-15. 

^ “Jewelry Central”. http://www.jewelrycentral.com/Target_Coral.asp. Retrieved 2007-02-15. 

^  ”Coral”. Encyclopdia Britannica (11th ed.). 1911. 

^ “Passage from Ovid’s Metamorphoses about the origin of coral”. http://findarticles.com/p/articles/mi_m0422/is_2_81/ai_55174794/pg_34. Retrieved 2007-03-18. 

External links

www.arkive.org Photos of living red corals and skeletons (Accessed 02 February 2007)

International Colored Gemstone Association Extensive info on gemstone coral and jewelry photos (Accessed 02 February 2007)

American Gem Trade Association Information on coral as a gemstone (Accessed 02 February 2007)

Organic Gems: Red Coral Jewelry Photos of raw coral material and coral jewelry (Accessed 02 February 2007)

Mediterranean red coral: research team International Research Team on Mediterranean red coral (Accessed 15 March 2007)

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Jewellery

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Corals and coral reefs

Stony corals

Scleractinia  Hermatypic coral  Blue coral  Brain coral  Pillar coral  Staghorn coral  Table coral

Soft corals

Alcyonacea  Black coral  Bamboo coral  Organ pipe coral  Sea fans  Sea pens

Coral diseases

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Coral reefs

Atoll reef  Cay  Fringing reef  Microatoll  Coral reef fish  The Structure and Distribution of Coral Reefs

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Protection

Coral reef protection  Project AWARE  Reef Check  Reef Ball  Coral Reef Alliance  International Society for Reef Studies

Other

Coral biology  Coral dermatitis  Coral (precious)  Coral rag  Coral sand  Coralline algae  Fire coral  Rugosa (extinct)  Tabulate (extinct)  Zooxanthella

Categories: Anthozoa | Gemstones

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