Species and varieties
Beryl is beryllium aluminum cyclosilicate (Be₃Al₂Si₆O₁₈). The gem varieties are aquamarine (blue to blue-green), morganite (pink to orange-pink), heliodor (yellow), goshenite (colorless), and emerald (green, colored by chromium and vanadium). Red beryl ("bixbite") is a minor variety with very limited commercial production.
Mohs hardness is 7.5 to 8; specific gravity is 2.66 to 2.87 depending on alkali content. Beryl is uniaxial and negative.
Sources
- Brazil — Minas Gerais produces aquamarine, morganite, and heliodor at commercial scale.
- Madagascar — historic and ongoing source of morganite and aquamarine.
- Mozambique — increasingly important since the 2010s for aquamarine and morganite.
- Pakistan — Shigar Valley aquamarine, often elongated crystals.
- Colombia — Muzo, Chivor, Coscuez: the historic and continuing primary source of fine emerald.
- Zambia — Kafubu mining area produces commercially significant emerald with bluish-green tone.
- Ukraine — Volyn region heliodor.
Treatments
- Aquamarine is commonly heat-treated to remove green overtones and shift to a purer blue. Treatment is standard and is rarely declared.
- Morganite is sometimes heat-treated to remove yellow-orange tones; treatment is similarly common.
- Emerald is frequently oiled or resin-filled to fill surface-reaching fractures. The practice is widespread in the trade; higher-end retailers typically declare the treatment and grade the filling.
- Synthetic emerald (hydrothermal, flux-grown) has been produced commercially since the mid-20th century. Identification of synthetic emerald is performed in laboratory under magnification and with spectroscopic analysis.
Lapidary considerations
Aquamarine and morganite cut cleanly with diamond grits and polish well with cerium oxide or fine diamond paste. Emerald presents particular lapidary challenges because of the typical fracturing of natural material and the practice of fracture-filling, which can react with cutting and polishing fluids.
Beryl is dichroic; orientation during preform layout affects the apparent color of the finished stone. The closed-c-axis orientation typically produces stronger color in aquamarine.