Royal Ontario Museum Polarised-Light Microscopy Laboratory

Orthopyroxene Group


Crystal system: Orthorhombic
Refractive index: 1.650-1.788
Birefringence: 0.007-0.020
Cleavage: 2 good, 88o
Colour in PPL: Mg-rich colourless, Fe-rich reddish or greenish
Pleochroism: Mg-rich none, others weak to strong
Relief: moderate to high
Distinction: from clinopyroxenes by pleochroism, lower birefringence and straight extinction
Occurrence: ultra-mafic rocks and medium to high-grade metamorphic rocks

Minerals in the Orthopyroxene group are:

  • Enstatite
  • Orthoferrosilite


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