Sorosilicate · Biaxial (−)
Epidote in thin section
Pistachio yellow-green with high relief and bright interference colors (birefringence about 0.019–0.046). One good cleavage.
Plane-polarized light
| Color | Yellow, Green |
|---|---|
| Pleochroism (color change on rotation) | Weak, Strong |
| Relief | High |
| Cleavage | One |
| Shape | Prismatic, Anhedral / equant |
Cross-polarized light
| Maximum birefringence | about 0.035 |
|---|---|
| Highest interference color | 2nd-order blues, greens, 3rd-order |
| Extinction | Parallel, Inclined |
| Twinning | None, Simple (two halves) |
Telling it apart
Zoisite has parallel extinction. Clinozoisite is colorless with low, sometimes anomalous colors. Allanite is usually brown; piemontite is usually pink.
Where you'll find it
Greenschist, altered igneous rocks, skarn
Photo examples
Alex Strekeisen · 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