Emerald is the most valuable variety of the mineral beryl. Primarily green, it may also display tints of yellow or blue. Not enough green, and the stone will be classified as green beryl. Too much blue, and it will be called an aquamarine. Thus, the more pure green color the emerald displays, the more valuable it is. Its color is caused by impurity atoms of either chromium or vanadium, which are incorporated into beryl crystals as they grow. The 858ct Gachala Emerald crystal was found at the Vega de San Juan mine in Gachala, Colombia, in 1967. Rarely are emerald crystals of such size and superb color preserved; they are usually cut into gems. Harry Winston donated the Gachala Emerald to the Smithsonian in 1969.
