Emerald is the most precious stone in the beryle group. The name emerald comes from the Greek "smaragdos" via the Old French "esmeralde", and really just means 'green gemstone.' The wonderful green color of emerald is unparalleled in the gem world. It is not surprising then that emerald is classified as one of the traditional four precious stones along with sapphire, ruby and diamond. Emerald is the birthstone for May and for commemorating the 20th and 35th wedding anniversaries.
Emerald's precious green color is caused by trace amounts of chromium and vanadium.
Almost all natural emeralds contain characteristic inclusions. For that reason emeralds are generally more fragile than other beryls and must be handled more gently. Almost all emeralds are treated with oil or resins to fill tiny cracks. With emerald, even more than other colored gems, it is color which is the chief determinant of value.
Emerald, by definition, is a medium or darker green to blue green beryl, in which the green color is derived from impurities of chromium, vanadium, or a combination of both. The most popular and valuable color is a slightly bluish green in a medium dark tone with strong to vivid saturation. The term "Colombian" emerald is often been used to describe vivid, slightly bluish green stones of medium, to medium dark color, no matter what their actual geographic origin. Emeralds of lighter color are sometimes called "Brazilian" emerald, even if they were mined in Africa.
Emerald looks best in daylight. Artificial light will expose inclusions and fractures that prove the stone to be a natural emerald.
Clarity is important, but inclusions are tolerated more in emerald than virtually any other gem. Unlike other beryl gems, emeralds often contain inclusions and other flaws. These flaws are not looked on as negative aspects for emerald like 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.
Cutters love this unique gem. Indeed, they have developed a special cut just for this gem: the emerald cut. The clear design of this rectangular or square cut with its oblique corners brings out the beauty of this valuable gemstone to the full, at the same time protecting it from mechanical strain.
Emeralds are also cut in many other, mainly classical shapes, but if the raw material contains a large number of inclusions, it may often be cut into a gently rounded cabochon, or into one of the emerald beads, which are so popular in India. Clear, transparent specimens come sometimes as brilliant cuts.