Red Coral
Corallium rubrum · Organic Gem
Crystal System
Trigonal crystal system; microcrystalline structure with a branching, tree-like habit
Mineral Group
Carbonates (Organic Gemstone)
Chemical Formula
CaCO3 with MgCO3 and traces of Fe2O3 (Iron oxide) for pigmentation
Formation Process
Biogenic; formed by colonies of marine polyps that secrete a calcium carbonate skeleton over decades in deep-water environments
About This Crystal
Deep red to orange-pink body color, typically polished to a vitreous or waxy luster. The raw specimen shows a matte surface with natural pits and striations. It is opaque to slightly translucent at the edges.
Physical Characteristics
Color: Salmon red to oxblood; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.6 - 2.7; Fluorescence: Usually none, though some may show weak violet under LWUV
Optical Properties
Refractive Index: 1.486 - 1.658; Birefringence: 0.172 (often difficult to measure due to opacity); Uniaxial negative; No pleochroism
Hardness & Durability
Origin Region
Mediterranean Sea (Italy, Tunisia, Algeria), Sea of Japan, and Taiwanese waters
Hardness & Durability
Mohs Hardness: 3.5 - 4. Toughness is relatively good, but it is sensitive to heat and acids. Suitable for beads and cabochons rather than rings.
Care & Maintenance
Extremely sensitive to acids (perfume, sweat, vinegar). Clean with a soft, damp cloth only. Store in a soft pouch away from sunlight to prevent drying and fading.
Rarity & Value
Precious red coral is increasingly rare due to overharvesting. Value is determined by color uniformness (oxblood is most valuable), size, and lack of visible pits/boring holes from marine organisms.
Special Characteristics
Often shows a distinctive longitudinal wood-grain structure or faint concentric circles in cross-section. May contain natural cavities or 'pit marks' left by sponge borings.
Lore & History
Historically used as a protective amulet against the 'evil eye' in Mediterranean cultures. In Vedic astrology, it is associated with Mars (Mangal) and is believed to instill courage and vitality.