Ivory
Last updated: April 2026
Ivory is dentine from the tusks of elephants, mammoths, walrus, hippopotamus, and other mammals. In gemology, ivory identification is a legal tool: African and Asian elephant ivory is listed on CITES Appendix I (commercial trade illegal in most jurisdictions), while woolly mammoth ivory is legal to trade. Species determination is made by measuring the Schreger angle — the intersection angle of the cross-hatched lines visible on a cross-section under magnification. Elephant ivory: Schreger angle <115° (typically 90–110°). Mammoth ivory: Schreger angle >115° (typically 120–140°). GIA published a definitive comparative study (Gems & Gemology, Spring 2013). Vegetable ivory (tagua nut), bone, antler, and plastic are common imitations — all lack Schreger lines.
Ivory has a specific gravity of 1.85 and a refractive index of 1.535–1.540, with a Mohs hardness of 2.5–3.0. It is aggregate.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Related: Organic Varieties
Key Differentiators
- Schreger lines — cross-hatched pattern visible on cross-section: elephant <115°, mammoth >115°
- Grain pattern visible under magnification — concentric or engine-turned lines on longitudinal section
- Hot point test: burning hair/protein smell (not plastic)
- SG 1.70–1.98 — lower than most gem minerals
- LEGAL NOTE: Elephant ivory is CITES Appendix I (illegal trade); mammoth ivory is legal — species determination requires Schreger angle measurement
Common Simulants
- Howlite (dyed or undyed): White to cream, porous calcium borosilicate. Often dyed cream or stained to mimic ivory. SG 2.45–2.58 (heavier than ivory 1.70–1.98); lacks Schreger lines (cross-hatch UV fluorescence pattern diagnostic for true ivory). Hot point test: resin/plastic smell if fake.
- Serpentine: Light yellowish-green to cream serpentine used in carvings as ivory substitute. SG 2.44–2.62 (heavier than ivory); RI ~1.56–1.57 (higher). Lacks the characteristic Schreger lines seen in ivory under UV or low magnification.
Treatments
- Bleaching (hydrogen peroxide — whitens yellowed ivory)
- Dyeing or staining (may simulate age patina)
Measurement Guides
Identifying an ivory? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Ivory is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →