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Emerald Gemstone Information

Emerald is Greek for 'green stone' (Smaragdos) and has been mined for thousands of years. Gem quality emeralds are transparent stones with an attractive grass green colour and very few inclusions. These stones are very rare and expensive, as emeralds are often heavily included and commonly have surface reaching cavities. Some large faceted emeralds with highly visible dark inclusions appear on the market and command high prices. The most important attribute is again, the highly saturated grass green colour. The quality of emerald available to the gem market is wide, resulting in very cheap to enormously expensive stones.

Source locations for emerald include: Afghanistan, Africa, Australia, Brazil, Columbia, India, Madagascar, Pakistan and the USA.

Physical Properties

Stone type:
A variety of the species beryl.
Crystal System:
Hexagonal.
Chemical Composition:
Beryllium aluminium silicate Be3Al2(SiO3)6.
Colour:
The grass green colour is due to the presence of chromium. In some stones the colour is produced by Vanadium.
Lustre:
Vitreous.
Pleochroism:
Dichroic, seen as blue-green and yellow-green.
Dispersion:
Low.
Hardness:
7½ - 8 on the Mohs' scale of hardness.
Toughness:
Poor: Emerald is a hard but brittle gemstone, therefore the facet edges require protection; the emerald facet cut was designed for that purpose. Toughness is poor when heavily included, whereas a clear stone may have good resistance to damage. Thermal shock (sudden temperature change) may fracture a stone.
Cleavage:
None.
Density in gm/cc:
2.67-2.78
Double refraction:
Yes.
Refractive index:
1.565-1.602

Common Treatments

Emeralds may have been oiled to fill fractures that often go deep within the stone, this improves the clarity and colour. The oil may contain dye to further enhance the colour. This is a normal and accepted practice in some countries and must always be disclosed. Fractures may be filled with polymers and other materials: complete coatings are also applied.

Emeralds are also made synthetically by hydrothermal methods, fortunately detected by the lack of natural inclusions and the presence of wavy growth lines (Chevrons).


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