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Mohs hardness: 7.5-8
Refractive index: 1.57-1.6
Critical angle: 39.5°
Specific gravity: 2.65-2.75
Fracture: Conchoidal, tough
Dispersion: Medium (.014)
Heat sensitivity: None
Pleochroism: Dichroic Golden: weak (yellow to light-yellow); Goshenite: colorless, no dichroism; Green: distinct (yellow-green to blue-green); Heliodor: weak (gold-yellow to greenish-yellow); Morganite: distinct (pale-pink to lavender-pink); Purple: distinct (purple to colorless); Yellow: (light yellow to medium yellow).
Birefringence (double refraction): Weak (.006-.009)
Crystal structure: Hexagonal
Treatments: Aquamarine is usually heat treated to remove the greenish cast. Morganite may be heat treated to change the peachy coloring to pink and may also be irradiated. Bixbite and heliodor may be heat treated and irradiated. Goshenite may be heat treated. Emerald is almost always treated with some filling agent to reduce the visibility of inclusions. These treatments are controversial and there is no consensus as to which treatment, if any, is appropriate.
Cutting: Emerald and bixbite with heavy inclusions can break apart. Otherwise, beryl is probably the easiest stone to facet.
Polishing: Beryl polishes easily with alumina or cerium oxide.