gemstone

Red Coral (Sponge Coral / Apple Coral)

Corallium rubrum (calcium carbonate / organic gem)

AI-generated identification · may be incorrect

Hardness: 3.5 to 4 on the Mohs scale, Color: Vivid red, pinkish-red, often stabilized or dyed with web-like patterns, Luster: Vitreous when polished to waxy, Crystal Structure: Amorphous / organic skeletal structure, Specific Gravity: 2.60 to 2.70

Hardness: 3

Identified August 7, 2026More gemstone →

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Physical properties

Formation & geological history

Formed by marine colonial invertebrates (polyps) in warm-water marine environments, precipitating calcium carbonate skeletons over decades to centuries.

Uses & applications

Primarily used in jewelry, cabochons, carvings, and decorative beads.

Geological facts

Many red coral specimens seen in commercial jewelry are stabilized or dyed sea sponge coral or bamboo coral due to protective regulations on precious Mediterranean red coral.

Field identification & locations

Identified by its organic cellular matrix patterns and reactivity to dilute acid due to its calcium carbonate composition. Found in tropical marine regions and deep-sea beds.