Orthopyroxene: Enstatite-Ferrosilite series



General formula of orthopyroxene: (Mg,Fe)2[Si2O6]
Enstatite-Ferrosilite
nα=1.650- 1.768
nβ=1.653 - 1.770
nγ=1.658 - 1.788
δ=0.007 - 0.020
2V:
+(54-84)° - Enstatite
+84 - (-75)° - 'Bronzite'
- (75-55)° - 'Hypersthene'

 Relationship between 2V angle and composition of orthopyroxene.




Thin section pictures:
Orthopyroxene 'hypersthene'' (2V=-60°) in gabbro-diorite, Spencer Butte, Oregon

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