One of the most well-known and prized gemstones is the lustrous green emerald. An emerald is the gemstone variety of the mineral beryl whose characteristic deep green color is caused by the presence of chromium during the mineral’s formation. Color, clarity, and transparency are the most important factors when choosing one of these rare gemstones. Emeralds are highly prized when they display a pure, deep rich green fire and have clarity free from impurities visible to the eye. Emerald is the birthstone for May. This treasured gemstone is also a recommended gift for the 20th, 35th and 55th wedding anniversaries.