Epidote
(calcium aluminum iron silicate)
Color: Pistachio-green, yellow-brown and
blackish-brown.
Types/Color:
-
Clinozoisite - Light green to green-brown. (Contains
less iron.)
-
Piemontite - Opaque, cherry-red. (Contains
manganese.)
Moh’s hardness: 6-7
Refractive index: 1.733-1.768
Critical angle: 35°
Specific gravity: 3.25-3.5
Cleavage: Perfect in two directions.
Fracture: Uneven, brittle.
Dispersion: Moderately high (.03)
Heat sensitivity: Moderate
Pleochroism: Trichroic – Strong (green to
brown to yellow).
Birefringence (double refraction): Strong
(.04)
Crystal structure: Monoclinic
Cutting: Cutting is fairly straightforward.
Polishing: Alumina on standard polishing
laps.
Comments: Cleavage tends to separate with
heat during dopping. The twinning planes are even more susceptible to heat.
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