Organic Gemstone (Sedimentary classification)
Red Coral
Corallium rubrum (Calcium Carbonate, CaCO3)
Hardness: 3.5 - 4 on the Mohs scale; Color: Ranges from pale pink to deep oxblood red; Luster: Dull/matte in natural state, vitreous/glassy when polished; Structure: Amorphous/microcrystalline; Cleavage: None; Specific Gravity: 2.6 - 2.7.
- Hardness
- 3
- Color
- Ranges from pale pink to deep oxblood red
- Luster
- Dull/matte in natural state, vitreous/glassy when polished
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Physical properties
Hardness: 3.5 - 4 on the Mohs scale; Color: Ranges from pale pink to deep oxblood red; Luster: Dull/matte in natural state, vitreous/glassy when polished; Structure: Amorphous/microcrystalline; Cleavage: None; Specific Gravity: 2.6 - 2.7.
Formation & geological history
Formed by biological secretion of calcium carbonate skeletons by marine polyps in deep-sea colonies. Commonly found in tropical and subtropical waters. Geological age: Holocene (Modern), though fossilized varieties can be millions of years old.
Uses & applications
Primary use is in fine jewelry (carvings, beads, cabochons), traditional medicine in some cultures (as an ash or powder), and as a luxury collectible gemstone.
Geological facts
Red coral is known as 'Noble Coral' and is considered one of the seven treasures in Buddhist scripture. Unlike reef-building coral, Corallium rubrum grows in deep, dark caves and on rocky sea floors.
Field identification & locations
Identify in the field by looking for a characteristic fine, wood-grain-like growth structure under magnification. Common locations include the Mediterranean Sea, Sea of Japan, and the Taiwan Strait. Collectors should beware of 'bamboo coral' which is dyed to mimic this noble species.
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