Clinopyroxene · Biaxial (+)
Augite in thin section
High relief. Colorless, gray, pale green or pale brown, with no or weak pleochroism. Two cleavages at about 87°/93°. Extinction 35–48° in elongate sections, symmetrical in basal sections. Colors up to mid 2nd order (birefringence 0.018–0.034). Lamellar twins can combine into a herringbone pattern.
Plane-polarized light
| Color | Colorless, Green, Brown |
|---|---|
| Pleochroism (color change on rotation) | None, Weak |
| Relief | High |
| Cleavage | Two at ~90° |
| Shape | Prismatic, Euhedral, Anhedral / equant |
Cross-polarized light
| Maximum birefringence | about 0.026 |
|---|---|
| Highest interference color | 2nd-order blues, greens |
| Extinction | Inclined, Symmetric to cleavage |
| Twinning | Polysynthetic stripes, None |
Telling it apart
Orthopyroxene has lower birefringence and parallel extinction. Amphiboles have cleavages at 56°/124°. Olivine has no cleavage and higher birefringence.
Where you'll find it
Basalt, gabbro, andesite
Photo examples
Alex Strekeisen (clinopyroxene) · Univ. of Geneva · Search Wikimedia Commons
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