Emerald is one of the four recognized precious gemstones along with sapphire, ruby and diamond. The name of this unparalleled gem comes from the Greek word “smaragdos” and the Latin “smaragdus” which mean green gemstone.
Emerald Origin and Formation
Emerald is the green to greenish-blue variety of beryl family gemstones which form in igneous, metamorphic and sedimentary rocks under heat and pressure during hundreds of millions of years.
They are made of 4 elements such as beryllium, aluminium, silicon and oxygen. When the conditions deep in the Earth’s crust are just right these four elements form emerald crystals.
The green colour of emeralds is caused by the presence of chromium, vanadium or iron. If the gemstone is not dark enough and saturated enough it is not considered to be a true emerald. In such a case it is called green beryl.
The most highly valued emeralds have a pure green colour with vivid saturation with no visible colour variations throughout the stone.
Emeralds are mined from many locations around the world, such as the United States, Australia, Russia, Pakistan and Afganistan. However, the three major sources are Colombia, Brazil and Zambia.
Colombia is the most famous source of the finest deep green emeralds and it produces 70-90% of emeralds for the global market today. Brazilian emeralds are valued for their high clarity and slightly yellowish-green colour, while Zambian emeralds are desirable for their slightly bluish-green colour.
Colour is the chief determinant of value when talking about emeralds. It is evaluated by three components: hue, tonal grade and saturation.
Hue describes the type of green the emerald has, for example, bluish-green, yellowish-green etc.
Tonal grade refers to the level of lightness or darkness of the green, while saturation refers to the intensity of the colour.
There are many shades of emeralds from medium to dark green, blue-green and sometimes slightly yellowish or bluish-green. However, the most popular and valuable colour for emerald ranges from slightly bluish-green to pure green in a medium-dark tone with strong or vivid saturation.
Clarity is important for emeralds but inclusions are tolerated more than in any other gem. According to the Gemological Institute of America (GIA), emerald is Type III clarity gemstone, meaning that even good quality emeralds used in fine jewellery today are in I2 to I3 clarity range.
These imperfections are not looked upon as negative attributes as they would be for other gemstones. In opposite, these flaws are considered part of the character of emeralds and lack of any inclusions is often a sign of a fake emerald.
Unlike diamond, emerald clarity is graded by eye. If an emerald has no inclusions that are visible to the naked eye, it’s considered flawless.
Types of Emeralds
Emeralds are differentiated by their place of origin or the presence of a certain type of impurities.
As the name suggests, Colombian emeralds are mined in Colombia. These gems are known for their exceptional quality and high value.
Brazilian emeralds are mined in Brazil. They have a lighter green colour than those mined in Colombia. It is worth mentioning that the term “Brazilian emerald” sometimes refers to green tourmalines.
Zambian emeralds come from mines found in Zambia and they were not that accepted by the high-end market until 1989. But things have changed when Tiffany and Co. began to promote Zambian emeralds for their distinctive characteristics.
Cat’s Eye Emeralds
This type of emeralds got its name due to a cat’s eye effect called chatoyancy which is an optical reflectance effect caused by aligned inclusions in a stone. Cat’s eye emeralds are very rare and can be found only in paler green emeralds.
Star emeralds are extremely rare and most are found in either Brazil or Madagascar. This type of emeralds exhibits the rare occurrence of the asterism, which is the appearance of a rayed star moving inside of a gem.
Trapiche emeralds are the rarest type of emeralds, which are actually a combination of emeralds and lutite found in Colombia. Because of the hexagonal structure of emeralds, these two minerals alternate and form a pattern looking like the spokes on a wheel.
Emerald is one of the most valuable gemstones in the world. Being naturally included gemstones, emeralds are priced in a slightly different way than all other coloured gems.
The price of natural emeralds is mainly determined by their colour.
The most valuable stones have a green hue, vivid and deep tone, and not too dark or light saturation consistent throughout the gem.
Although emeralds can be cut into any shape, the cuts which enhance the gem’s natural colour and sparkle add its price.
Another price determinant is, of course, the size of the gem. Larger emeralds are harder to find so they are much more expensive than smaller ones.
And the final indicator for the price is the source of the emeralds. The gems that come from Colombia are the most valuable with those from Zambia and Brazil just behind.
|Chemical Name||Aluminium beryllium silicate|
|Colours||Emerald-green to green, yellowish-green to bluish-green|
|Hardness||7.5 - 8 on the Mohs scale|
|Refractive Index||1.565 - 1.602|
|Specific Gravity||2.7 - 2.8|
|Transparency||Transparent to opaque|