Mineralogical Properties of Emeralds

  Emeralds belong to the beryl family of minerals, consisting primarily of chemical element beryllium. They obtain their green coloring from trace amounts of other elements, either chromium and vanadium. Since beryllium occurs only in minute amounts in the earth’s crust, and not particularly frequently in combination with chromium or vanadium, emerald formation proves a miraculous and rare event.    

Mineralogical Properties of Emeralds

While pure beryl is colorless, emeralds contain traces of chromium or vanadium, which cast it in hues of green. If the specimen contains trace amounts of iron, the green displays overtones of bluish green or yellow, depending on the level of oxidation. (source) Typically, gem-quality emerald forms in hexagonal prisms. Colors range in hue from yellow-green to blue-green, with green as the primary color. Color is the most important grading factor for emerald. Since two different elements affect coloring, some experts argue whether stones colored by vanadium should be classified differently than those colored by vanadium. Indeed, some gemologists propose that the term emerald should only apply to those colored by chromium. They believe specimens owing their color to vanadium should be classified as green beryl. (source) This distinction carries over into the gemstone industry. To classify as emeralds, specimens must demonstrate a medium-to-dark tone. Indeed, the finest stones must range in tones greater than 75%, with 0% being colorless beryl and 100% being black. Since vanadium tends to produce paler green stones, most gem-quality specimens contain chromium as their coloring agent. (source)    

Grading Factors for Emeralds

As with most colored gemstones, color is the first and most important grading factor. High-quality emeralds display a deep verdant green with slightly blue-green or yellow-green overtones. As I mentioned before, pale specimens fall below emerald status. Experts categorize them as green beryl. Additionally, experts categorize light greenish-blue beryls as aquamarine, and yellow-green beryl is called heliodor. (source) Second only to color, the clarity of an emerald factors into its overall value. Ideally, emeralds should prove highly transparent and unobscured by visible inclusions. Notorious for containing multiple inclusions, including surface fissures, experts refrain from using a loupe to determine clarity. Instead, they use their eyes to ensure that in spite of these imperfections, they shimmer and shine throughout. Of course, cut and size also play their parts in valuation. As a result of the numerous inclusions and general fragility of emeralds, cutters often choose to step cut the best specimens. Emeralds also lend themselves well to the cabochon cut. Indeed, many designers have carved intricate and beautiful designs into emerald cabochons. Due to their miraculous formation and their incredible green color, emeralds remain one of the most popular gemstones around the world.

Which of these emerald jewels do you love best?

~Angela Magnotti Andrews