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.
Physical & Optical Properties
RI Range1.624–1.660
SG Range3.00–3.20
SG Typical3.10
Hardness (Mohs)7–7.5
Crystal SystemTrigonal
Optic CharacterDR Uniaxial (−)
Birefringence0.018
Dispersion0.017
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterRed
PleochroismStrong Dichroic
ColorsGreen
SpeciesTourmaline
VarietyChromian Dravite or Chromian Elbaite
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)
Price Context
Natural — low ($/ct)$200
Natural — high ($/ct)$3,000
NoteFine chrome tourmaline $200–3000/ct; Tanzania and Kenya stones with rich emerald green command premiums. Rarer than verdelite.
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a chrome tourmaline? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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