Kyanite (Al₂SiO₅) is a triclinic aluminum silicate famous for its bladed habit and intense blue color, ranging from sky-blue to deep sapphire-blue. It is one of three Al₂SiO₅ polymorphs (with andalusite and sillimanite) — each forming at different metamorphic pressure-temperature conditions. Kyanite is the diagnostic high-pressure indicator. Its anisotropic hardness (4.5 along the c-axis, 7 across) is unusual among minerals and earned it the historical name “disthene” (two strengths).
Key Facts
- Mohs hardness 4.5–7 — anisotropic; harder across the blade than along its length.
- Triclinic; bladed and tabular crystal habit.
- Diagnostic blue color from iron substitution; green and orange varieties also exist.
- Forms in regional metamorphic schists and gneisses at high pressure.
- Industrial source of mullite and refractory aluminosilicates.
Notable Localities
Pizzo Forno (Switzerland) and Minas Gerais (Brazil) produce world-class blue blades. Petaca pegmatite (New Mexico) and Yancey Co. (North Carolina, USA) yield classic American material.
Found at these Localities
- Swiss Alps (Alpine-Cleft Province) (瑞士阿尔卑斯高山裂隙矿物产地)
- Eastern Brazilian Pegmatite Province (巴西东部伟晶岩省)
