Clinozoisite-Epidote thin section

Relief: High positive (both clinozoisite and epidote)
Habit/Form: Often found as anhedral grains or granular aggregates. Crystals are columnar, prismatic, bladed, or acicular with the long dimension parallel to the b axis. Columnar or radial aggregates are relatively common. Sections through crystals are usually six-sided or rectangular. Detrital grains are usually rounded or platy parallel to the basal cleavage. Oriented intergrowths with zoisite may be found, as can grains with brown allanite cores and epidote rims.
Color: Clinozoisite is colorless; epidote is colorless, pale yellow, pale green, greenish yellow, yellowish green
Pleochroism: Colourless to yellow and green.
Cleavage: Perfect basal cleavage {001}.

Isotropy/Anisotropy: Anisotropic
Interference color: Clinozoisite – order I gray, white and yellow; often anomalous blue or yellow-brown.
Epidote – order II – III (very bright or ‘fluorescent’); increasing with increase in iron content. The maximum interference colors range from low second-order to upper third-order colors.
Extinction angle: Parallel / 0° / straight to length of elongate crystals and inclined excinction relative to its {001} cleavage (0-25° for the clinozoisite and 25-40° for the epidote).
Twins: Multiple normal twinning on {100} is moderately common.
Uniaxial/Biaxial: Biaxial, Clinozoisite (+) and Epidote (-)
Optic axial angle (2V): Clinozoisite 2V measured: 14 – 90°, calculated: 72 – 86°
Epidote 2V measured: 90 – 116°, calculated: 62 – 84°