Almost all-natural emeralds contain distinct characteristic inclusions and almost all are treated with oil or resin to fill tiny fissures and cracks. It is the presence of these flaws and oil which makes it quite easy to identify and distinguish natural emeralds amongst other similar gemstones. Artificial light will expose and amplify inclusions and fractures that prove the stone to be a natural emerald. Emerald color is owed to trace amounts of chromium and vanadium, and color is best admired under natural daylight. One of the easiest methods to identify green emeralds is to test for specific gravity (density) and hardness. Like all forms of beryl, emerald is harder than apatite, quartz and feldspar, but is slightly softer than spinel, topaz and sapphire. However, emerald is generally more fragile than other beryl, owing to its naturally included state.
With emeralds, even more so than other colored gems, it is the color that is the chief determinant of value. By definition, emeralds are a medium to darker green to blue-green and sometimes slightly yellowish-green beryl. Emeralds owe their fine green color to traces of chromium and/or vanadium impurities. The most popular and valuable color is a slightly bluish green in a medium dark tone with strong to vivid saturation, however, too much blue can decrease the value.
The term “Colombian emeralds” is often used to describe vivid, slightly bluish-green stones of a medium to medium dark color, regardless of their geographic origin. Emeralds of a lighter color are sometimes called “Brazilian emeralds”, even if they were mined in Africa.
Emerald Clarity and Luster
Emeralds have a vitreous (glass-like) luster when cut and polished. Although their clarity can occur from translucent to opaque, transparent specimens are most desirable and are much more valuable. Clarity is important, but inclusions are tolerated more in emeralds than virtually any other gem. Unlike other beryl gems, emeralds often contain inclusions and other flaws. These flaws are not looked upon as negative attributes for emeralds, as they would be for other gemstones. Indeed, these flaws are considered part of the character of the stone and are used to assure the purchaser of a natural stone.
Emerald clarity is graded by eye, unlike diamond, where 10x loupe magnification is used to grade clarity. If an emerald has no inclusions that are visible to the naked eye, it is considered flawless. “Eye-clean” stones will command the highest prices, especially those with ideal color grade.
Emerald Cut and Shape
Emeralds are most often cut in a special cut designed just for this gem; “the emerald-cut”. The emerald cut is a step-cut or trap-cut featuring a rectangular or square shape with truncated corners. This cutting style maximizes the beauty and color of the stone, whilst protecting it from mechanical strain and internal stress. Emeralds are also cut into a variety of other traditional shapes such as pear, oval and round. Lower grade materials are often cut in cabochon or into beads. Highly transparent and clear materials are sometimes cut in brilliant-style.
Oiling is a common emerald treatment and, in most cases, it is done right at the mining location. The term ‘oiling’ refers to the practice of immersing emeralds in a colorless oil or resin (most often cedar oil) in order to enhance color, clarity and stability. This is also often done using a vacuum chamber to assist penetration. Non-standard treatments go beyond this by using colored oils and epoxy-like resins.
These treatments dramatically improve the appearance of the gems but necessitate special care in cleaning and setting. Steam cleaners, solvents and ultrasonic cleaners can remove the oils, making inclusions that were barely visible stand out in sharp relief. Since emeralds can be restored through re-oiling, the damage is considered to be only temporary.
Synthetic emeralds have been available since 1848. In the 1950s, synthesizing methods became commercialized and excellent quality synthetics have been made available since. The term ‘Chatham emeralds’ is often used for lab-grown emeralds. There are also numerous emerald doublets available. In many cases, a natural upper-half is cemented to a glass or synthetic pavilion using an emerald-green paste. With the visibility of emerald flaws from the crown down, once these are set into jewelry, they are often sold as natural emeralds.
Emerald Gemological Properties:
|Species:||Emerald – beryl|
|Chemical Formula:||Al2Be3Si6O18 – Aluminum beryllium silicate|
|Crystal Structure:||Hexagonal; hexagonal prisms|
|Color:||Emerald green to green to slightly bluish or yellowish-green|
|Hardness:||7.5 to 8 on the Mohs scale|
|Refractive Index:||1.565 to 1.602|
|Density:||2.67 to 2.78|
|Transparency:||Transparent to opaque|
|Double Refraction or Birefringence:||-0.006|
Emerald: Related or Similar Gemstones:
Emerald belongs to the important group of beryl gemstones. There are quite a few different gemstone-quality varieties of beryl, most of which are classified based on color and coloring agents, such as pink morganite and red bixbite. There are also many other green colored gemstones that can be confused with green emerald, including green aventurine quartz, demantoid garnet, tsavorite, chrome tourmaline, chrome diopside, grossularite garnet, uvarovite garnet, verdelite, fluorite, hiddenite and peridot.
Most Popular Related Gemstones:
Lesser-Known Related Gemstones:
Goshenite, morganite, heliodor, bixbite and ‘trapiche emerald’ are lesser-known related gemstones.