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Color: Brown, yellow, green, brownish-red.
Moh’s hardness: 5-5.5
Refractive index: 1.995-2.05
Critical angle: 30.5°
Specific gravity: 3.52-3.54
Fracture: conchoidal, brittle
Dispersion: Very strong (.051)
Heat sensitivity: None
Pleochroism: Dichroic - Medium to strong (green to pale-green or colorless and yellow-reddish to brownish-red or colorless).
Birefringence (double refraction): Very strong (.105-.135)
Crystal structure: Monoclinic
Cutting: If a twinning plane is present, orient it just below the girdle and parallel with the table.
Polishing: Alumina on tin/lead or tin oxide on tin lap.
Comments: Clean rough is difficult to find, but cut stones are stunning due to the high RI and dispersion.