Iolite
Famous for its extreme pleochroism, showing different colors when viewed from different directions.
Physical & Optical Properties
RI Range1.542–1.551
SG Range2.57–2.66
SG Typical2.59
Hardness (Mohs)7–7.5
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (−)
Birefringence0.009
Dispersion0.017
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismStrong Trichroic
ColorsBlue Violet, Purple
SpeciesCordierite
Key Differentiators
- Extreme pleochroism
- RI near quartz but DR
- Often has inclusions
Common Simulants
- Blue sapphire: Sapphire: uniaxial negative; RI 1.762–1.778; SG 4.00; dichroic (not trichroic); much harder (9 Mohs).
- Tanzanite: Tanzanite: biaxial positive; RI 1.691–1.700; SG 3.35; trichroism blue-violet-burgundy; softer (6.5 Mohs).
Price Context
Natural — low ($/ct)$20
Natural — high ($/ct)$100
NotePer carat; undervalued gem; strong pleochroism is the key diagnostic feature
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
About Iolite
Famous for its extreme pleochroism, showing different colors when viewed from different directions.
Identifying a iolite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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