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Euclase (beryllium aluminum silicate)
Color: Colorless, light blue, sea green yellow.
Moh’s hardness: 7.5
Refractive index: 1.652-1.672
Critical angle: 36°
Specific gravity: 3.0-3.1
Cleavage: Very perfect in 1 direction.
Fracture: Conchoidal, uneven, brittle.
Dispersion: Medium (.016)
Heat sensitivity: None
Pleochroism: Dichroic - very weak (different depth of green).
Birefringence (double refraction): Medium (.02)
Crystal structure: Monoclinic
Cutting: Cutting is fairly straightforward if you orient away from the cleavage plane.
Polishing: Tin oxide or alumina on common polishing laps.