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Emerald

Last updated: April 2026

Emerald is the green to greenish-blue variety of beryl.

Emerald has a specific gravity of 2.72 and a refractive index of 1.565–1.602, with a Mohs hardness of 7.5–8.0. It is uniaxial −.

Physical & Optical Properties

RI Range1.565–1.602
SG Range2.67–2.78
SG Typical2.72
Hardness (Mohs)7.5–8
Crystal SystemHexagonal
Optic CharacterDR Uniaxial (−)
Birefringence0.006
Dispersion0.014
Fluorescence LWVariable
Fluorescence SWInert
Chelsea FilterVariable
PleochroismStrong Dichroic
ColorsGreen
SpeciesBeryl
Green

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

Emerald varies 1.565 – 1.602 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°, reading both edges atevery 45°. SEETwo boundaries 0.006 apart — so close that at this size theyread as one thick line. On the instrument they separate onlywith a steady head and a sharp edge. The pair drawn here isone specimen: this species is published at 1.565 – 1.602,and the two edges slide together anywhere across it, betweenthe dashed marks. MEANSThat gap IS the birefringence — and it is the stable part.Where the pair sits varies by 3 printed divisions from stoneto stone, so the gap identifies and the position onlynarrows. Take max minus min across the whole rotation; asingle position understates it. 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

Emerald Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Emerald blinks light-dark four times in a full turn. That is doubly refractive. It does NOT tell you uniaxial from biaxial — that is the optic figure, which needs a conoscope. 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

Emerald SG 2.67–2.78 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 21 other species in the table overlap this range, so a reading here narrows the field to 22 rather than naming the stone. Combine it with a refractive index to separate what is left. 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

Emerald Two colours (dichroic) BEST ORIENTATION ROTATED 45° — THE NULL At its best orientation Emerald shows bluish-green in one window and yellowish-green in the other. Rotate the instrument 45° and the two windows become IDENTICAL — the null. So "both windows the same" means either the stone is singly refractive or you are holding the instrument at the wrong angle, and the only way to tell is to turn it. 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.

AquamarineGosheniteHeliodorMorganiteRed Beryl

Key Differentiators

Natural vs. Synthetic

Synthetic emerald is commercially available (Flux (Chatham, Gilson), Hydrothermal (Biron, Linde/Regency, Pool), Lechleitner overgrowth). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Emerald.

Common Simulants

Commonly Confused With

Commonly confused with: Tourmaline, Glass, Synthetic Spinel, Tsavorite Garnet, Chrome Diopside, Fluorite, YAG.

Treatments

Related Comparisons

Emerald Vs TsavoriteNatural Vs Synthetic Emerald

Measurement Guides

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

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

Try Loupewise Free →

Studying for the GIA, FGA, or FEEG practical? Emerald 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 →