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
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: Tourmaline Varieties
Key Differentiators
- Strong pleochroism
- Elongated crystals with striations
- Liquid-filled inclusions (trichites)
Common Simulants
- Emerald: Emerald: uniaxial negative; RI 1.577–1.583; SG 2.72; Chelsea filter red; characteristic jardin inclusions.
- Ruby: Ruby: uniaxial negative; RI 1.762–1.770; SG 4.00; Chelsea filter strongly red; strong UV fluorescence.
- Sapphire: Sapphire: uniaxial negative; RI 1.762–1.770; SG 4.00; much higher RI than tourmaline.
- Glass: Isotropic; gas bubbles under loupe; no pleochroism; conchoidal fracture.
Commonly Confused With
Commonly confused with: Emerald, Ruby, Sapphire, Glass, Almandine Garnet, Peridot, Tsavorite Garnet.
Treatments
- Heat Treatment (to lighten or clarify)
- Irradiation (to deepen color)
- Surface Coating (Paraiba imitation)
Related Comparisons
Measurement Guides
Identifying a tourmaline? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →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.
Practice exams →