Actinolite (calcium magnesium iron silicate)
Color: light to medium green.
Moh’s hardness: 5-6
Refractive index: 1.61
Critical angle: 38°
Specific gravity: 3.03-3.07
Cleavage: Perfect, two directions, cleaves very easily.
Heat sensitivity: Low
Pleochroism: Dichroic. Light to medium green.
Birefringence (double refraction): medium (.026)
Crystal structure: Monoclinic
Cutting: Cut with an extra fine lap. Sharp corners tend to fray. C axis cuts slower and smoother than A/B axis.
Polishing: Alumina on tin or tin/lead at slow speed.