The emerald gemstone is a variety of the beryl mineral. The beryl turns green due to chromium and vanadium impurities. There are several different types of emeralds, most of which are named for their country of origin.
Columbian emeralds are mined in Columbia. These emeralds are known for their exceptional quality.
Brazilian emeralds are lighter green gemstones that are mined in Brazil. The term "Brazilian emerald" sometimes refers to green tourmalines.
Cat's Eye Emeralds
These emeralds have a cat's eye effect, called a chatoyancy, which looks like a wide slit similar to the pupil in a cat's eye. Cat's eye emeralds are very rare and only found in paler green emeralds.
Trapiche emeralds contain black impurities that form a six-rayed star. This unusual type of emerald is mined only in the Muzo area of Columbia.
The term "star emeralds" typically refers to trapiche emeralds. The term is sometimes used to describe the rare occurrence of asterism, or the appearance of a rayed star moving inside of an emerald.
Emeralds are very sensitive to any type of pressure. The "emerald cut" was designed specifically to reduce the amount of pressure put on emeralds during cutting.