Kyanite

(Cyanite) (Disthene)
Chemistry: Aluminum silicate.
Crystal system: Triclinic; long flat bladed prisms; fibrous.
Color: Transparent to translucent; blue, colorless, blue/green.
Hardness: 5 – 7 (directional) 7 across the crystal; 5 along its length.
Cleavage: Perfect: 1 direction, parallel to large prism face; Fracture: brittle, fibrous.
Specific gravity: 3.65 – 3.69
Refractive index: 1.715 – 1.732; Biaxial negative; 0.017
Luster: Vitreous.
Dispersion: Low
Dichroism: Distinct: light blue, colorless, dark blue.
Occurrence: urIn schists and gneisses or granite pegmatites; Burma, India, Brazil, Kenya, USA, Pakistan.

Notes
Polymorph with andalusite and sillimanite (fibrolite); fluorescence: variable; spectral line in deep red and 2 lines in deep blue; faceted.