Coral
Last updated: April 2026
An organic gemstone formed from the skeletal remains of marine polyps.
Coral has a specific gravity of 2.68 and a refractive index of 1.486–1.658, with a Mohs hardness of 3.0–4.0. It is aggregate.
Physical & Optical Properties
RI Range1.486–1.658
SG Range2.60–2.70
SG Typical2.68
Hardness (Mohs)3–4
Crystal SystemAggregate
Optic CharacterAggregate
Dispersion0.000
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsRed Pink, Colorless, Black, Blue Violet
SpeciesOrganic
Related: Organic Varieties
Key Differentiators
- Organic origin (skeletal material)
- Often shows a wood-grain like structure
- Effervesces in acid
Treatments
- Bleaching (to whiten)
- Dyeing (to redden or deepen color)
- Imitation (plastic, dyed bone, dyed howlite)
Price Context
Natural — low ($/ct)$10
Natural — high ($/ct)$200
NotePer piece (not per carat); ox-blood red coral commands highest prices; CITES restrictions apply
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a coral? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Coral is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →