If polished, such a specimen displays asterism or chatoyancy . Pure Beryl is colorless. However, a wide range of impurities cause the diverse amount of colors. The green in Emeralds are caused by traces of chromium, and the blue in Aquamarines are caused by iron. Huge, opaque, crystallized hunks of Beryl occur, and these are useful for extracting the rare metal beryllium.
Beryllium is a very tough metal, and is used in alloys to strengthen the metal.
Beryl forms some of the most well-known and prized gems. The deep green variety Emerald is one of the most valuable of gems. Aquamarine, a semi-precious gem, is the most popular light blue gem. Other Beryl varieties are also faceted for the gem market. Fine shaped Beryl crystals are very popular among mineral collectors.