Coral
JewelryWiki Editorial·3 sources·Reviewed 2026-08-04
An organic gem. Like pearl, damaged by heat, light and household chemicals rather than by scratching.
Properties
| Property | Value | Authority |
|---|---|---|
| Refractive index | 1.486–1.658 [1] | — |
| Specific gravity | 2.60–2.70 [1] | — |
| Common treatments | Bleached, dyed, and coated — sometimes all three in sequence. GIA describes black or “horn” coral bleached and then coated with relatively thick artificial resin to protect the material and intensify its colour, and shows a coral branch partially dipped in bleach to produce a golden colour before resin coating. Coral is also among the materials dyed since ancient times. [3] | — |
| Care cautions | NEVER use an ultrasonic cleaner. GIA groups this with the organic gem materials — pearls, coral, tortoise shell, ivory, shell cameos, jet and amber — which are porous and can be damaged both by the heat of an ultrasonic and by the chemicals in most cleaning solutions. Warm soapy water only. [2] | — |
Sources
- International Gem Society — reference charts (Mohs hardness, specific gravity, refractive index) — International Gem Society (IGS reference charts)
- GIA — Ultrasonic Cleaners for Gems: What You Need to Know — Gemological Institute of America (GIA 4Cs, Ultrasonic Cleaners for Gems)
- GIA — An Introduction to Gem Treatments — Gemological Institute of America (GIA, An Introduction to Gem Treatments (Robert Weldon))