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Tourmaline

Last updated: April 2026

Elbaite tourmaline occurs in a wide range of colors with strong pleochroism. Named color varieties: Rubellite (red/pink), Indicolite (blue), Verdelite (green), Paraiba (neon blue-green, Cu-bearing), Watermelon (pink core, green rim), Chrome Tourmaline (Cr-green). All share the same species RI/SG and cannot be distinguished by standard measurements alone — color and provenance separate them. No pleochroic colour pair is recorded for tourmaline because the species has no single body colour: the difference is one of DEPTH rather than hue, and the ordinary ray is always the darker of the two whatever the colour (GIA, Pleochroism in Tourmaline). In dark brown stones one dichroscope window can look practically black — a textbook-correct reading, not a fault (Anderson 1958, p. 238).

Tourmaline has a specific gravity of 3.06 and a refractive index of 1.624–1.644, with a Mohs hardness of 7.0–7.5. It is uniaxial −.

Physical & Optical Properties

RI Range1.624–1.644
SG Range3.01–3.26
SG Typical3.06
Hardness (Mohs)7–7.5
Crystal SystemTrigonal
Optic CharacterDR Uniaxial (−)
Birefringence0.020
Dispersion0.017
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterVariable
PleochroismStrong Dichroic
ColorsRed Pink, Green, Blue Violet, Yellow Orange, Brown, Black, Colorless, Multi
SpeciesTourmaline
Red PinkGreenBlue VioletYellow OrangeBrownBlackColorlessMulti

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

Tourmaline reads 1.624 – 1.644 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, 0.020 apart at their widest separation. MEANSThat gap IS the birefringence. Take max minus min across thewhole rotation — a single position understates it, so onereading is an incomplete one. 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

Tourmaline Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Tourmaline 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

Tourmaline SG 3.01–3.26 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 19 other species in the table overlap this range, so a reading here narrows the field to 20 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

Tourmaline strong dichroic — colours not recorded COLOURS NOT IN OUR SOURCE Tourmaline is recorded as showing strong dichroic pleochroism, but our source does not name the two colours, so this figure does not paint them. The windows will differ; which hues they take is not something we hold. 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.

Chrome TourmalineGreen TourmalineIndicoliteParaiba TourmalineRubelliteWatermelon Tourmaline

Key Differentiators

Common Simulants

Commonly Confused With

Commonly confused with: Emerald, Ruby, Sapphire, Glass, Almandine Garnet, Peridot, Tsavorite Garnet.

Treatments

Related Comparisons

Paraiba Tourmaline Vs Apatite

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Tourmaline 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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