Emerald: description, properties and photo
Emerald is a green variety of beryl mineral and a popular precious stone. In is the most expensive type of beryl. The name means from various languages ”green stone”. Chromium impurities, presented in its composition, paint this stone in green color. The content in the structure of vanadium is a reason of bluish shades. If the color of beryl is caused by the iron content, then these stones cannot be considered as emeralds. The most valued color is saturated green or bluish-green. The color of the stone can be describe as “grass-green.” Very light or very dark emeralds, as well as with a yellowish tint, are valued less. The best classical green emeralds are mined in Colombia.
Gem-quality emeralds are quite rare in nature. Crystals has the form of columnar hexagonal prisms. Its hardness is very good – 7.5-8 on the Mohs scale. However, the optical properties and characteristics of the stone are such that it rarely has good transparency. Natural stones almost always contain a large amount of cracks and inclusions. That is why almost all volume of mined rough emeralds are treared by oiling or polimer impregnation due to make them less visible. Evaluation of clarity is not very strict. Large amount of cracks, despite high hardness, make this stone very fragile. The stone can be considered as unique if characteristics of color and clarity are very high and it weights more than 5 ct. The cost of such emeralds may exceed $ 10,000 per carat.
In classification you can see description of rare cat’s eye and trapiche varieties of emerald. Trapiche emerald has sectors separated by dark inclusions of graphite in cross section of crystal. This impurities create 6 rays, going from the center of crystal. Emeralds of this type got their name from the word “trapiche” – that means a grinding wheel that was used in South America to process sugar cane. The largest specimens of trapiche with good quality rarely exceed weight of 10 carats. Many collectors and lovers of original jewelry hunt for such stones. Today, green beryl is very popular in Russia. It is believed that the observation of the pleasant green color of this stone has a calming effect. Many owners of jewelry with emeralds notice this property in everyday life.
One of the best color emeralds are mined in Colombia. Colombian emerald is a brand in the world of precious stones, synonymous with high quality. Samples of excellent color also come from other fields. For example, from Afghanistan, Brazil or Zambia. Rough material of not large size is mined in Pakistan. In Russia, the green beryl deposit is located in the Urals near the settlement of Malysheva. Emeralds there are mined together with alexandrites. But uralian emeralds are quite difficult to find in the world market. Today, the majority of crystals comes from Colombia and Zambia, where are find the largest gem-quality stones.
Mohs scale hardness:
very imperfect in one direction
- The more cracks in the emerald go to the surface of the stone, the stronger the degree of oiling will be.
- The most valuable are emeralds with saturated green or bluish-green color.
The history of the stone begins in 330 BC, when the development of emerald mines in Egypt began, which had been lasted until the 1700s. Queen Cleopatra used them to create jewelry. A Roman scientist Pliny the Elder described its physical properties in the 1st century AD, noting that people used green emeralds to relax, relieve stress and eye strain when you look at these stones. The history of the gem is also associated with the Incas, who used emerald jewelry in their religious rites. The Spaniards, on the other hand, exchanged precious metals for Inca emeralds, which they then brought to Europe and Asia. Legend said that the emerald had been one of the four gems given by God to King Solomon. Nowadays, it is one of the most popular gems, their spring green color attracts many of gemstone and jewelry lovers.
More than 90 % of emeralds on the gemstone market are treated with aim of clarity improving. For this, cracks are filled with cedar oil or various polymers. Oiling is a standard classic method of emerald treatment. Filling with colorless oil is allowed as common practice, green oil is not approved by the gemological community. Coloration with various types of dyes is sometimes applied for almost opaque very light green beryls. Treated samples cost significantly less than untreated with the same characteristics. Price also depends on the degree of filling with various substances. Filling can be diagnosed by spectra, when other chemical impurities related to the filling substance, and not included in the formula of emerald, can be seen in the composition. The more filling substance is in the stone, the lower the price is.
In the photo: pear-shaped stone weighted more than 10 ct, Colombian origin
In the photo: rough emeralds (fragment of crystals)
In the image: rare variety «trapiche», cabochons
In the photo: bright emerald in octagon shape of cutting 4.22 ct
Set of faceted emeralds from Afghanistan