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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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