Crystal system: Monoclinic system
Refractive index: 1.715-1.797
Birefringence: 0.015-0.049
Cleavage: one perfect
Twinning: lamellar, not common
Colour in PPL: yellow-green
Pleochroism: colourless to greenish yellow
Relief: high to very high
Distinction: from hornblende and clinopyroxenes by single cleavage, higher birefringence, and characteristic pleochroism
Occurrence: principally regionally-metamorphosed rocks