Red coral is the common name for Corallium rubrum and several related species of marine coral. The distinguishing characteristic of precious corals is their durable and intensely red or pink skeleton that is often used for making jewelry.
Red corals grow on rocky seabed with low sedimentation, typically in dark environments-either in the depths or in dark caves and gorges. The original species, C. rubrum (formerly Gorgonia nobilis), is found mainly in the Mediterranean. It grows at a depth of 10 to 300 meters below sea level, although the shallow parts of these habitats have largely been “fished out”. In the underwater caves of Alghero, Sardinia (the “Riviera del Corallo”) grows at a depth of 4 to 35 meters. The same species is also found at Atlantic sites near the Strait of Gibraltar and the Cape Verde Islands. Other Corallium species are native to the western Pacific, especially around Japan (Corallium japonicum) and Taiwan. These are located at a depth of 350 to 1500 meters below sea level in areas with strong currents.
As with other Gorgonacea, blood corals have the shape of small leafless bushes and grow up to a meter long. Their valuable skeleton is composed of interlocking spicules of hard calcium carbonate, colored in red by carotenoid pigments. In living specimens, the skeletal branches covered with a soft, bright red shell, from which numerous retractable white polyps protrude. The polyps exhibit octameric radial symmetry. Another precious marine product pearls, totally different in appearance, but chemically very similar.
Coral as a gemstone
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 dark red, the word coral is also used to call such colors. Because of its intense and permanent color and shine, the precious coral skeletons since ancient times from the sea removed for decorative use. At that time it was for traders who were looking coral customary to say to shop owners: “I must have the precious”. Include coral jewelry found in ancient Egyptian tombs and prehistoric Europe, and are still made today. It was especially popular during the Victorian era.
Blood Coral has a specific gravity of 3.86 and hardness of 3.5 on the Mohs scale. Due to its softness and opacity, coral is usually ‘and cabochon’ cut, or used to make beads.