Sorosilicate · Biaxial (+)
Clinozoisite / zoisite in thin section
Colorless, high relief, low birefringence (clinozoisite about 0.004–0.015, zoisite about 0.006–0.018), sometimes with anomalous blue or greenish-yellow colors. One perfect cleavage.
Plane-polarized light
| Color | Colorless |
|---|---|
| Pleochroism (color change on rotation) | None |
| Relief | High |
| Cleavage | One |
| Shape | Prismatic, Anhedral / equant |
Cross-polarized light
| Maximum birefringence | about 0.010 |
|---|---|
| Highest interference color | 1st-order gray–white, 1st-order yellow–red, Anomalous (inky blue / brown) |
| Extinction | Inclined, Parallel |
| Twinning | None, Polysynthetic stripes |
Telling it apart
Epidote is yellow-green with brighter colors.
Where you'll find it
Greenschist, amphibolite, altered plagioclase
Photo examples
Univ. of Geneva (clinozoisite) · Search Wikimedia Commons
Photos open on the source sites.
Identify an unknown grain Read interference colors Practice mineral ID
Related minerals
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