Emerald is the green variety of Beryl and is the most prized and valuable of all the varieties. It is most commonly opaque to translucent, but when it is transparent and gemmy, it is one of the most sought after and precious gems in the gem/jewelry trade. The intense deep green color is the result of trace quantities of Chromium. It often occurs in association with Calcite, Quartz, Pyrite, Biotite, Schorl and Beryl.
The crystal system for Emerald is hexagonal, often forming perfect six-sided hexagons with flat terminations. Other forms include columnar aggregates and massive.
The finest Emeralds generally come from Columbia. Other notable locations include Afghanistan, Brazil, China, the USA (North Carolina) and Zambia.