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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

RI Range1.535–1.540
SG Range1.70–1.98
SG Typical1.85
Hardness (Mohs)2.5–3
Crystal SystemAggregate
Optic CharacterAggregate
Fluorescence LWWeak blue-white
Fluorescence SWInert
Chelsea FilterNot Applicable
PleochroismNone
ColorsColorless, Yellow Orange, Brown
SpeciesOrganic
VarietyIvory (Elephant / Mammoth)
ColorlessYellow OrangeBrown

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

Ivory reads 1.538 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORotate the stone through a full 360°, watching the boundary. SEEOne boundary, at 1.538, and it does not move as you rotate. MEANSThis is an aggregate — a mass of microscopic crystals — andon this instrument it looks exactly like a singly refractivestone. The refractometer cannot tell the two apart. Thepolariscope can: an aggregate stays light through a fullrotation, where a singly refractive stone stays dark. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

Through the polariscope

Ivory No reading ANY POSITION — THE STONE BLOCKS THE LIGHT BETWEEN CROSSED POLARS Ivory is opaque, so no light reaches the analyser. The field stays dark in every position — not because the stone is singly refractive, but because the test cannot be run on it at all. SR, DR and aggregate cannot be separated this way. Computed from optic character and transparency in gems.json. A polariscope separates singly refractive, doubly refractive and aggregate — it does not show the optic sign.

Drawn from the optic character and transparency above. A polariscope separates singly refractive, doubly refractive and aggregate; the optic sign needs a conoscope. How to take this reading.

Specific gravity, and what it rules out

Ivory SG 1.70–1.98 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 3 other species in the table overlap this range, so a reading here narrows the field to 4 rather than naming the stone. Combine it with a refractive index to separate what is left. Ivory is porous: it soaks up water during immersion, which raises the weight in water and makes the SG read HIGH. Heavy liquids damage porous material, so there is no clean fallback — treat any figure here as unreliable. Computed from the specific-gravity range in gems.json. Hydrostatic weighing — the bench method this site recommends; heavy liquids are toxic and regulated. Faint ticks are the other species in the table.

Drawn from the specific-gravity range above, against every other species in the table. How to take this reading.

Through the dichroscope

Ivory No reading NO LIGHT THROUGH THE STONE Ivory is opaque. A dichroscope reads light that has passed THROUGH the stone, so there is nothing to split and no reading to take — the same limit that rules out the polariscope. Computed from pleochroism and pleochroic colours in gems.json. Window tints are derived mechanically from the colour words, not chosen; a neutral pair depicts no colour at all.

Drawn from the pleochroism above. Two windows that match mean either no pleochroism or the wrong angle — turn the instrument to tell. How the dichroscope compares.

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Key Differentiators

Common Simulants

Treatments

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

Identifying an ivory? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

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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.

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