Emeralds, the birthstone for those born in May, come in many shades of green and bluish green. Emeralds exhibit a wide spectrum of clarity, depending on the inclusions and fractures in the crystal. Clear stones with dark yet vibrant color command the highest prices. Almost all emeralds contain numerous flaws, cracks, and inclusions, which can negatively affect the clarity. As with other gemstones, the value of an emerald depends on cut, color, clarity, and carat. Flawless emeralds are exceptionally rare, and therefore command great prices (in some instances, higher than diamonds).

Most emeralds are oiled as part of the post lapidary process in order to improve their clarity. Cedar oil, having a similar refractive index, is often used in this generally accepted practice. The U.S. Federal Trade Commission requires the disclosure of this treatment when a treated emerald is sold. The use of green-tinted oil is generally not considered acceptable by the gem trade.