Chemistry and Crystallography
Chemical Composition |
Be3Al2SiO6 |
Crystallographic System |
Hexagonal |
Cleavage |
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Fracture |
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Fracture Lustre |
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Habit |
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Physical Characteristics
Hardness |
7.5 to 8 |
Toughness |
poor to good |
Specific Gravity |
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Streak |
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Optical Characteristics
Colour and Cause |
Green; Chromium is the usual element claimed to be responsible for the attractive green colour of emerald. However, some emeralds from Colombia, Russia, Lake Manyara(Tanzania), Afghanistan, Nigeria, Zambia, and Carnaiba(Brazil) are characterised by unusually low contents of chromium. Indeed, some of these emeralds contain up to about 0.3% V2O3, which also may contribute to their emerald green colour(Brown, 1984; Platonov et al., 1984; Wood and Nassau, 1968). The large variation of iron content in emeralds is due to the possibility of incorporating iron, either as Fe2+ and or Fe3+, in different sites in the beryl lattice. Indeed specimens of bluish green Zambian emerald were quite distinct from other emeralds analysed as they have the highest iron content but low concentrations of chromium.
Both colombian emeralds and the synthetic emerald had less FeO than all other emeralds. In addition, the Colombian Emeralds contained considerable amounts of CuO. Bluish green Zambian emerald and emeralds from Carnaiba(Brazil) both had lower chromium contents than emerald from other locations. Some emeralds from Afghanistan and Brazil were slightly enriched in iron as well as vanadium.
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Degree of Transparency |
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Polish Lustre |
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Refractive Index |
1.56 to 1.60 |
Birefringence |
0.003 to 0.010 |
Optic Character |
Uniaxial negative |
Pleochroism |
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Dispersion |
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Phenomena |
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X-Ray Fluorescence |
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Transparency to X-Rays |
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Ultraviolet Fluorescence |
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Chelsea Filter Reaction |
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Absorption Spectra |
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Description
Appearance |
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Variety and Trade Names |
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Misnomers |
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Typical Size Range |
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Typical Cutting Styles |
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Market
Availability |
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Public Recognition |
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Wearability |
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Recommended Disclosures |
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Key Separations, Suggestions for Testing and Evaluation
Emerald imitations can be made from green glass or synthetic spinel triplets.
Synthetic emeralds may be grown using the flux of hydrothermal method.
Emerald alternatives include alexandrite, demantoid garnet, diopside, jadeite, Peridot, sapphire, tourmaline, tsavorite garnet, and zircon.
Possibilities for Confusion
Bibliography and Suggested Further Reading
- Peter G. Read, Gemmology
- http://www.gia.edu/library/4463/emerald.cfm