The colors in beryls come from trace elements in the crystals.
Beryl is a most alluring and popular mineral. It occurs in a diversity of colors, and has several important gemstone varieties. The green variety, Emerald, is one of the most precious gems. Only green Beryl with a deep green color is called Emerald; light green Beryl is simply "Green Beryl" (or Heliodor if it has a yellowish color.)
Aquamarine, another important gemstone, is the greenish-blue to blue variety of Beryl. Green Beryl from certain localities can be heat treated to produce sky-blue Aquamarine. Other popular gem varieties of Beryl are the pink Morganite, and the yellow Heliodor and Golden Beryl. A deep red variety of Beryl, known as Red Beryl (or Bixbite) is extremely rare, and only comes from two localities in Utah. When in good specimens, Red Beryl commands an outstanding premium and is very difficult to obtain.
Pure Beryl is colorless. However, a wide range of impurities cause the diverse amount of colors and many varieties. The green color in Emerald is usually caused by traces of the elementchromium, and the blue color of Aquamarine usually by iron.
Beryl is naturally transparent, however inclusions and impurities may make it opaque. All gemmytransparent varieties are highly valued, but the other forms of Beryl in opaque crystals are much more common. Some of the largest natural crystals known are of Beryl, with enormous crystals having been found in several pegmatite occurrences.