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Large Square Cut Cornered Emerald
Emerald
Emerald is the grass green variety of the gemstone called beryl.
Beryl occurs in various colours, as follows:
ColourGemstone
Grass greenEmerald
Sea blueAquamarine
YellowHeliodor or Golden Beryl
PinkMorganite
ColourlessGoshenite
VioletBeryl
BlueBeryl
Pale GreenBeryl

All the stones listed in the above table are different varieties of beryl, and share many characteristics.
Although all emeralds are beryl, not all beryls are emerald.

Colouration
Pure beryl is colourless, often called white, and although quite rare, tends not to be valuable because it does not have much brilliance. Colours, as in many gemstones, are caused by small amounts of impurity, usually metallic oxides. This is a another case where impurity is desirable.
Chromium, in the form of chromic oxide, causes the bright grassy green colouring in beryl, thereby producing emeralds.
Vanadium can also affect the exact shade, as may traces of iron.
It is also possible to have green beryl which is not emerald, because the colouring agent is not chromium.

Hardness
Emerald, along with other beryls, is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.

Sources
The earliest known source of emerald was near the Red Sea in Egypt, the so-called Cleopatra's emerald mines. They were probably worked from about 2000 B.C., apparently the location of them was lost in the middle ages, and not rediscovered until 1818. Most emeralds used in ancient jewellery are believed to have come from these mines. They are not worked nowadays because of the low quality of crystals found.
Emeralds have been found in Austria since Roman times, in the Legbach ravine at Habachtal near Salzburg. These are no longer commercially mined.
Columbia is generally recognised as the source of the world's finest quality emeralds, both in the past and the present. The Columbian Indians were using them before 1537, when Quesada conquered Columbia. Later the Spanish discovered that the emrald mines were at Somondoco, which means "god of the green stones", and which is now known as Chivor. The best coloured Columbian emeralds are said to be those from the Muzo mine, although another mine at Cosquez is also highly rated.
Russia has been another important source of emeralds in the past. Most Russian emeralds coming from Sverdlovsk or Ekaterinburg in the Ural Mountains.
Emeralds were discovered in Australia in 1890 in New South Wales.
Emeralds were discovered between1927 and 1929 at Gravelotte in South Africa, followed by other sources.
Another important source of superb quality emeralds, usually only of small size, is Sandawana in Zimbabwe formerly Southern Rhodesia. These were discovered only in 1956.
Emeralds were known in India from antiquity, but their source is not certain. The earliest known Indian source was 1929 at Arawalli in Rajahstan, other sources being discovered since. The quality of Indian emeralds is very variable, but most are of lower quality which are often polished as beads.
Other sources of emerald include Norway, North Carolina, Connecticut, Maine, New Hampshire, although non of these are very important.

Prices
The price range of emeralds is very large, ranging from under 1 pound per carat to many thousands of pounds per carat, depending primarily on colour, but also on brilliance and clarity.
Large, brilliant clear emeralds are very rare and expensive, in fact any clear emerald is quite scarce, regardless of size.
In 2000, auctioneers Christies sold a 10 carat emerald for over $1 million, equal to over $100,000 per carat.

The Best and Most Valuable Colour
Many people seem to believe that the darker the emerald the better, just as many seem to believe the opposite. Neither of these opinions is correct. If you think, even briefly, about this it becomes obvious why. A very dark emerald would appear black, and would not be very attractive or desirable. The darkness often being caused by inclusions. An extremely pale emerald would be colourless, and not particularly attractive or valuable.
As usual, the truth lies between the two extremes. The most desirable emeralds are generally those with an intense grassy green colour, plenty of sparkle and life, and free of any inclusions. Some experts say that a dark velvety green is the most valuable.
Ultimately which is "best" is a subjective matter, and personal preference is important. Our usual advice to potential customers is to buy whichever colour of emerald they personally find the most attractive. We also think it's slightly sad that we need to give this advice. Buy what you like, using your own judgment, rather than allowing yourself to be a slave to fashion and buying what you think will impress other people.
The main choice in the colour of emeralds depends largely whether you prefer lighter but brighter stones, or a deeper more intense colour.

Oiling or Filling The vast majority of emeralds are oiled, that is to say, immersed in oil which fills the many cracks and fissures to which emerald is prone. This has the effect of reducing the visibility of the inclusions, and improving the clarity of the stone. Sometimes oiling also improves the colour. Green coloured oil is sometimes used to enhance the stones natural colour, there are also other fillers used which are more permanent than oil.
Because oil filling of emeralds has become almost universal, it is generally not considered essential to disclose this fact. We suggest that anyone wishing to buy a high quality or expensive emerald should request a gemstone laboratory certificate stating that the stone is natural and not oiled, but be prepared to pay extra for a certificated stone.
Most modern emeralds are likely to be oiled at the mines, and again at the cutters.

Cleaning
Emerald jewellery can be carefully cleaned using warm soapy water, or detergent, rinse thoroughly afterwards as detergents can cause dermatitis and allergic reactions. Enzyme cleaners should be avoided for the same reasons. Brushing with an old tooth brush to remove dirt and grease will also help. Cleaning agents containing chlorine may have a detrimental effect on low carat gold alloys, so are best avoided.
We stress that reasonable care should be taken when cleaning emeralds, as washing with strong detergents could cause any oil to be diluted or removed, requiring the stone to be re-oiled.
Emeralds do not like excessive heat, and although they can tolerate temperatures above 100c (the boioling point of water), it is advisable to use warm water rather than hot water, to reduce the dangers of thermal shock.
It is not advisable to clean emeralds in an ultrasonic tank. We sometimes risk it with our own stock, but we would never clean a large or valuable emerald which did not belong to us, in an ultrasonic machine.

Repair Work
Because of emeralds sensitivity to high temperatures and rapid temperature change, it is somewhat risky to carry out soldering close to emeralds when carrying out jewellery repairs. It is possible for emeralds to be coated with borax, or proprietary heat-shielding material while carrying soldering work on the jewellery in which they are set, but this must be done carefully, and if the emeralds are large or of very high quality, it is better to unset them before carrying out repair work involving heat. Naturally this itself carries some degree of risk. For this reason, it is best to treat emerald jewellery with greater care and respect than for tougher stones such as diamond, sapphire or ruby.
The mounts should be of good quality alloy such as eighteen carat gold or platinum, not nine carat. Expect to pay more for repair work on emerald jewellery than for similar work on other stones.

Technical Data
Chemical Composition and NameBe3Al2(SiO3)6 - Beryllium Aluminium Silicate
Hardness7.5 to 8
Refractive Index1.560 - 1.565 to 1.587 to 1.593
Specific Gravity2.65 to 2.76
Birefringence0.005 to 0.009
Crystalline SystemHexagonal
Optic SignNegative
Other Optical PropertiesUniaxial

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