Clinopyroxene

Mineral Name	Diopside	Augite	Pigeonite
Crystal System	Monoclinic	Monoclinic	Monoclinic
Chemical Comp..	CaMgSi2O6	(CaNa,Mg,Fe,Al,Ti)2Si2O6	(Mg,Fe,Ca)2Si2O6
Color	Colorless	Colorless/Pale Green	Colorless
Pleochroism	None	Weak Brown-Green	None/Weak Yellow
Cleavage	2@90˚ in basal	2@90˚ in basal	2@90˚ in basal
Relief	Moderate	Moderate	Moderate
Birefringence	High 1st/Low 2nd Order	High 1st/Low 2nd Order	Moderate-High 1st Order
2V	38˚-48˚	25˚-83˚	0˚-30˚
Optic Sign	Positive	Positive	Positive
Twinning	Simple & Multiple	Simple & Multiple	Simple or Lamellar

The top two photomicrographs show the weak pale green pleochroism of Clinopyroxene. The bottom photomicrograph shows that even though the cleavage planes are vertical (aligned N-S), the crystal is still in illumination under cross polarized light.




Series of photomicrographs showing the weak pleochroism of Clinopyroxene (top two photomicrographs, taken in plane polarized light). The bottom photomicrograph (taken in cross polarized light) demonstrates the higher birefringence of Clinopyroxene compared to Orthopyroxene, as well as the fact that it does not exhibit straight extinction.