Clinopyroxene (augite)

Chain silicate

Crystal system: monoclinic (+)

Colour in hand specimen: black 
Cleavage: two at 90° 
Hardness: 5.5-6

Colour in plane polarised light: colourless, pale brown or pale grey 
Pleochroism: variable weak to moderate 
Relief: moderate 
Birefringence: 0.018-0.033; 1^st order pink to 2^nd order orange 
Extinction: inclined 
Twinning: simple, common

L141 Gabbro 
L161 Basalt, amygdaloidal 
L162 Basalt, porphyritic 
L172 Ultramafic cumulate

Clinopyroxene contains calcium. It encompasses a range of solid solutions from (Mg,Fe)₂[Si₂O₆] to Ca(Mg,Fe)[Si₂O₆]. The physical and optical properties detailed above refer to augite, a clinopyroxene common in mafic igneous rocks.