Chrome Tourmaline
Last updated: April 2026
Chrome tourmaline is colored by Cr³⁺ rather than iron, producing a rich emerald-like green. The Chelsea filter red reaction is the fastest field diagnostic. Primary sources are Tanzania, Kenya, and Pakistan. Rarer and more valuable than ordinary verdelite.
Chrome Tourmaline has a specific gravity of 3.10 and a refractive index of 1.624–1.660, 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
- Chelsea filter RED — chromium coloring causes strong red reaction, unlike Fe-colored verdelite
- Rich emerald-like green from Cr³⁺; more saturated than Fe-colored green tourmaline
- Chromium absorption bands at ~637nm on spectroscope
- Strong dichroism; growth tubes and two-phase inclusions under loupe
Common Simulants
- Emerald: Beryl RI 1.577–1.583, SG 2.71; also Chelsea red, but much lower RI and SG than tourmaline
- Tsavorite Garnet: Isotropic (SR), RI 1.740, SG 3.61; Chelsea red; no dichroism; much higher RI than tourmaline
- Chrome Diopside: Monoclinic DR_B+, RI 1.664–1.730, birefringence 0.030; may show Chelsea red; different RI and crystal system
- Chromium-Doped Glass: Isotropic, gas bubbles, no natural inclusions; may show Chelsea red if Cr-doped
Treatments
- Heat Treatment
- Irradiation (rare)
Measurement Guides
Identifying a chrome tourmaline? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Chrome 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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