| Mineral Name |
Enstatite |
Hypersthene |
| Crystal System |
Orthorhombic | Orthorhombic |
| Chemical Comp.. |
Mg2Si2O6 | Fe2Si2O6 |
| Color |
Colorless |
Pale Pink |
| Pleochroism |
None |
Pale Pink-Green |
| Cleavage |
2@90˚
in basal |
2@90˚ in basal |
| Relief |
Moderate | Moderate |
| Birefringence |
Low 1st order |
Low 1st Order |
| 2V | 55˚-90˚ |
110˚-130˚ |
| Optic Sign | Positive | Negative |
| Twinning |
None | None |
Orthopyroxene is usually a mixture (solid solution) of Enstatite and Hypersthene.
Orthopyroxene exhibits first order birefringence (grey-yellow), cleavage present, orthorhombic = straight/symmetrical extinction.
This sequence of 3 photomicrographs demonstrates the straight extinction of Orthopyroxene (cleavage is aligned vertically or N-S in the first photomicrograph taken in plane polarized light). The second and third photomicrographs are under cross polarized light. The third photomicrograph is rotated slightly to show the low first order birefringence charactersitic of Orthopyroxene.
This sequence of 3 photomicrographs shows symmetrical extinction of Orthopyroxene and also the low first order birefringence. The first photomicrograph is taken under plane polarized light and the last two are under cross polarized light.