Axinite (calcium aluminum boro-silicate)
Color: blue, violet-blue, brownish and reddish-brown.
Moh’s hardness: 6.5-7
Refractive index: 1.68-1.723
Critical angle: 36.5°
Specific gravity: 3.26-3.41
Cleavage: Perfect in one direction.
Heat sensitivity: None
Pleochroism: Trichroic – Strong (olive-green to reddish-brown to yellowish-brown).
Birefringence (double refraction): Medium (.01)
Crystal structure: Triclinic
Cutting: Can be problematic to cut.
Polishing: Most common polishing laps with alumina or cerium oxide.
Comments: Orient for best color. Expect to deal with inclusions.