Indicolite
Last updated: April 2026
Blue to greenish-blue elbaite tourmaline. Separated from blue sapphire by much lower RI and strong birefringence producing facet doubling. Differs from aquamarine by stronger dichroism, higher SG, and facet doubling. Generally inert to LW UV. No commercial synthetic.
Physical & Optical Properties
RI Range1.624–1.644
SG Range3.02–3.10
SG Typical3.06
Hardness (Mohs)7–7.5
Crystal SystemTrigonal
Optic CharacterDR Uniaxial (−)
Birefringence0.018
Dispersion0.017
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismStrong Dichroic
ColorsBlue Violet
SpeciesTourmaline
Related: Tourmaline Varieties
Key Differentiators
- Strong dichroism — dark blue vs. light blue/colorless when rotated
- Blue with greenish modifier typical; both ends of dichroscope visible
- Birefringent — facet doubling visible under 10×
- Lower RI than sapphire (1.762) or aquamarine (1.577–1.590)
Common Simulants
- Blue sapphire: Sapphire: uniaxial negative; RI 1.762–1.778; SG 4.00; dichroic; much higher RI; harder (9 Mohs); no facet doubling.
- Aquamarine: Aquamarine: uniaxial negative; RI 1.577–1.590; SG 2.72; weaker pleochroism; lower RI; no facet doubling visible at 10×.
- Iolite: Iolite: biaxial negative; RI 1.542–1.551; SG 2.58–2.66; lower RI; trichroic (blue/yellow-grey/colorless), not dichroic.
- Blue Glass: Isotropic; no dichroism; gas bubbles under loupe; conchoidal fracture; no facet doubling.
Commonly Confused With
Commonly confused with: Sapphire, Aquamarine, Glass.
Treatments
- Heat Treatment (to lighten dark blue or remove brownish modifiers)
- Irradiation (to deepen or alter blue color)
Price Context
Natural — low ($/ct)$50
Natural — high ($/ct)$500
NotePer carat; clean vivid pure blue commands premium; greenish-blue more common; Nigerian and Brazilian material noted
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying an indicolite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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