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Phenacite or Phenakite (beryllium silicate)
Color: colorless, pinkish, wine-yellow.
Moh’s hardness: 7.5-8
Refractive index: 1.6-1.82
Critical angle: 38.5° for low RI and 33.5° for high RI.
Specific gravity: 2.95-2.97
Cleavage: Imperfect, but distinct in two directions.
Dispersion: Medium (.015).
Heat sensitivity: None.
Pleochroism: Dichroic – Definite (colorless, orangish-yellow).
Birefringence (double refraction): Medium (.016)
Crystal structure: hexagonal, trigonal
Cutting: Cuts easily.
Polishing: Slow to polish. Alumina on tin/lead or tin oxide on tin lap.