Orthopyroxene · Biaxial (±)
Orthopyroxene in thin section
High relief, pyroxene cleavages at about 88°, parallel extinction and 1st-order colors (birefringence about 0.009–0.011). Pink-to-green pleochroism is diagnostic when present. Fine exsolution lamellae are common.
Plane-polarized light
| Color | Colorless, Pink, Green |
|---|---|
| Pleochroism (color change on rotation) | None, Weak |
| Relief | High |
| Cleavage | Two at ~90° |
| Shape | Prismatic, Anhedral / equant |
Cross-polarized light
| Maximum birefringence | about 0.010 |
|---|---|
| Highest interference color | 1st-order gray–white, 1st-order yellow–red |
| Extinction | Parallel, Symmetric to cleavage |
| Twinning | None, Polysynthetic stripes |
Telling it apart
Clinopyroxene has inclined extinction and higher birefringence. Andalusite can look like enstatite but lacks pyroxene cleavage.
Where you'll find it
Gabbro, norite, peridotite, andesite, granulite
Photo examples
Photos open on the source sites.
Identify an unknown grain Read interference colors Practice mineral ID
Sources
OpticMin, ATHENA, Univ. of Geneva (P. Perroud) · Alex Strekeisen thin-section collection · Distinguishing features of minerals (UT Arlington) · MIT OCW 12.109 amphibole lab · SEPM Strata: carbonate staining · Wikipedia mineral pages (infobox optical data) · Athabasca University rocks and minerals · Smith College petrography: perthite