Kyanite
Last updated: April 2026
Blue aluminum silicate commonly confused with sapphire or tanzanite. Uniquely among gemstones, kyanite has direction-dependent hardness: 4.5 along the bladed crystal length (c-axis) and 6.5–7.0 across it. This anisotropic hardness is a diagnostic field indicator.
Physical & Optical Properties
RI Range1.712–1.734
SG Range3.53–3.68
SG Typical3.68
Hardness (Mohs)4.5–7
Crystal SystemTriclinic
Optic CharacterDR Biaxial (−)
Birefringence0.016
Dispersion0.020
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismStrong Trichroic
ColorsBlue Violet, Colorless, Green
SpeciesKyanite
Key Differentiators
- Variable hardness by direction — 4.5 along crystal length, 6.5–7.0 across (unique among gemstones)
- RI 1.710–1.734 — distinctly lower than sapphire (1.762–1.778)
- Strong trichroism: colorless / dark blue / violet-blue
- Bladed crystal habit, perfect cleavage in two directions
- SG 3.65–3.70 — heavier than tanzanite (3.35–3.38)
Price Context
Natural — low ($/ct)$10
Natural — high ($/ct)$200
NotePer carat; fine blue specimens command higher prices
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a kyanite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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