The emerald is appreciated for its gem varieties ranging from pale green and aquamarine to vivid emerald green and light pink morganite. Its hardness makes the emerald more scratch and damage resistant than other gemstones; however, it is also brittle and full of fissures that make setting the stone a difficult process. These and numerous other characteristics and properties of emeralds make it one the most sought-after and valuable gemstones on the market.
Emeralds contain fine inclusions which are small fractures that form within the crystal as it grows. These inclusions add color and distinction to the emerald and often add value to the stone as a result. According to gemstone specialists at the International Colored Gemstone Association, the inclusions are referred to as 'jardin'--French for garden--because they grow naturally like a garden within the stone.
Emeralds are tough stones with a hardness ranking of 7.5 to 8 on the Mohs Scale where 10 is the hardest. This makes the emerald a durable stone once it's set for jewelry. However, with the hardness comes the drawback of brittleness which makes the emerald easily damaged during the cutting process. A specific cut called the emerald cut is commonly employed to shape the emerald. It features beveled edges and rectangular shapes to keep from destroying the stone. The brittleness of an emerald depends on the amount of inclusions it contains and dictates the type of cut best suited for an emerald in raw form. The harder the stone, the more rounded the cut must be.
Emeralds contain the rare element called beryllium. Beryllium is a metal element with an atomic number of 4 that can only be formed chemically through reactions between granitic rocks and rocks that lack normal amounts of silica. When these rocks contain the elements chromium or vanadium, the beryl reacts through developing different intensities of color in the rocks. These reactions allow for the wide variations in the green, blue, salmon and pink hues specifically associated with emeralds.
The beauty of emeralds is not measured by their clarity but rather their color. Additional minerals, crystals and defects are also considered inclusions that make one emerald different from the next. The more 'defects' an emerald contains, the more intense its depth of color. According to gemstone specialists of the International Colored Gemstone Association, emeralds full of inclusions in deep, lively green hues still have a much higher value than an almost flawless emerald whose colour is clear and pale.
The luster of emeralds is described throughout the industry as vitreous. The term describes the shine of the emerald as glass-like and it varies depending on the emerald's natural refractivity--geometric ratio of the angle at which light hits the crystal--transparency and structure. Emeralds typically rank between 1.5 to 1.6 on the refractive scale. In comparison, the refraction rate of a diamond is 2.4. However, it's the color intensity of the emerald that give it a specific level of of luster and refraction which, in many cases, is more valuable than the price of a diamond.