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

Identified March 24, 2026More organic gemstone (sedimentary classification) →

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Physical properties

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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