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Coral (precious)

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Coral (precious)

For the red coral mushroom, see Ramaria araiospora.
Precious coral
Corallium rubrum
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Subclass: Alcyonaria
Order: Gorgonacea
Family: Coralliidae
Genus: Corallium
Species

About 25 species, see below.

Precious coral or red coral is the common name given to Corallium rubrum and several related species of marine coral. The distinguishing characteristic of precious corals is their durable and intensely colored red or pink skeleton, which is used for making jewelry.

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 (formerly Gorgonia nobilis), is found mainly in the Mediterranean Sea. It grows at depths from 10 to 300 meters below sea level, although the shallower of these habitats have been largely depleted by harvesting.[1] In the underwater caves of Alghero, Sardinia (the "Coral Riviera") it grows at depth from -4 mt to -35 mt. The same species is also found at Atlantic sites near the Strait of Gibraltar and at the Cape Verde Islands.[1] Other Corallium species are native to the western Pacific, notably around Japan (Corallium japonicum) and Taiwan;[2] these occur at depths of 350 to 1500 meters below sea level in areas with strong currents.[1]

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.[1] In living specimens, the skeletal branches are overlaid with soft bright red integument, from which numerous retractable white polyps protrude.[3] The polyps exhibit octameric radial symmetry.

Another precious marine material, pearl, although drastically different in appearance, chemically is very similar, also being mostly calcium carbonate deposited by marine invertebrates.[2]

Species

The following are known species in the genus:[4]

  • Corallium abyssale Bayer, 1956
  • Corallium borneanse Bayer
  • Corallium boshuense Kishinouye, 1903
  • Corallium ducale Bayer
  • Corallium elatius Ridley, 1882
  • Corallium halmaheirense Hickson, 1907
  • Corallium imperiale Bayer
  • Corallium johnsoni Gray, 1860
  • Corallium kishinouyei Bayer, 1996
  • Corallium konojoi Kishinouye, 1903
  • Corallium laauense Bayer, 1956
  • Corallium maderense (Johnson, 1899)
  • Corallium medea Bayer, 1964
  • Corallium niobe Bayer, 1964
  • Corallium niveum Bayer, 1956
  • Corallium porcellanum Pasternak, 1981
  • Corallium pusillum Kishinouye, 1903
  • Corallium regale Bayer, 1956
  • Corallium reginae Hickson, 1907
  • Corallium rubrum (Linnaeus, 1758)
  • Corallium secundum Dana, 1846
  • Corallium sulcatum Kishinouye, 1903
  • Corallium tricolor (Johnson, 1899)
  • Corallium vanderbilti Boone, 1933
  • Corallium variabile (Thomson & Henderson, 1906)

Coral as a gemstone



The hard skeleton of red coral branches is naturally matte, but can be polished to a glassy shine.[2] 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 jewellery has been found in ancient Egyptian and prehistoric European burials,[3] and continues to be made to the present day. It was especially popular during the Victorian age.[5]

Precious coral has relative density of 3.86 and hardness 3.5 on the Mohs scale.[6] 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 1st millennium, there was significant trade in coral between the Mediterranean and India, where it was highly prized as a substance believed to be endowed with mysterious sacred properties. Pliny the Elder remarks that, before the great demand from India, the Gauls used it for the ornamentation of their weapons and helmets; but by his period, 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. The belief in Coral's potency as a charm continued throughout the Middle Ages and even early in 20th century Italy it was worn as a protection from the Evil eye, and by women as a cure for Infertility.

From the Middle Ages onwards, the securing of the right to the coral fisheries off the African coasts was the object of considerable rivalry among the Mediterranean communities of Europe. Before the 16th century they were controlled by the Italian republics. For a short period the Tunisian fisheries were secured by Charles V for Spain; but the monopoly soon fell into the hands of the French, who held the right until the Revolutionary government in 1793 threw the trade open. For a short period (about 1806) the British government controlled the fisheries, but this later returned to the hands of the French authorities. Before the French Revolution much of the coral trade was centred in Marseille, but then largely moved to Italy, where the procuring of the raw material and the working of it was centring in Naples, Rome and Genoa.[7]

Coral in culture

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.[8]

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.

  • In Hindu astrology red coral is associated with the planet Mars or Graha-Mangala and used for pleasing Mars. It should be worn on the ring finger.
  • A branch of red coral figures prominently in the civic coat of arms of the town of Alghero, Italy.

Conservation

Intensive fishing, particularly in shallow waters, has damaged this species along the Mediterranean coastline, where colonies at depths of less than 50 metres are much diminished. Fishing and now climate change threaten their persistence. The three oldest Mediterranean Marine Protected Areas—Banyuls, Carry-le-Rouet and Scandola, off the island of Corsica—all host substantial populations of C. rubrum. Since protection was established, colonies have grown in size and number at shallow and deeper depths.[9][10]

See also

References

External links

  • International Colored Gemstone Association Extensive info on gemstone coral and jewelry photos (Accessed 2 February 2007)
  • American Gem Trade Association Information on coral as a gemstone (Accessed 2 February 2007)
  • Organic Gems: Red Coral Jewelry Photos of raw coral material and coral jewelry (Accessed 2 February 2007)
  • Mediterranean red coral: research team International Research Team on Mediterranean red coral (Accessed 15 March 2007)
  • The state of red coral (Corallium rubrum) populations in the N.W. Sardinian fishing grounds(Accessed 16 September 2010)
  • FAO
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