Beryl is a family of minerals; they all share the same basic formula and structure, but have diffferent impurites within their structure. The impurities and the concentration of the impurities gives them different colours and different degrees of opacity. All members of the family are a beryllium aluminium silicates and form hexagonal crystals. Beryls are generally a result of metasomatism -- changes to a rock due to the movement of hot fluids. They are is generally found in pegmatites within granitic rocks.