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.
Indicolite 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 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 (1.577–1.583)
Common Simulants
- Blue sapphire: Sapphire: uniaxial negative; RI 1.762–1.770; SG 4.00; dichroic; much higher RI; harder (9 Mohs); no facet doubling.
- Aquamarine: Aquamarine: uniaxial negative; RI 1.577–1.583; SG 2.72; weaker pleochroism; lower RI; no facet doubling visible at 10×.
- Iolite: Iolite: biaxial negative; RI 1.54–1.56; SG 2.57–2.66; 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)
Measurement Guides
Identifying an indicolite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Indicolite 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 →