Beryl is composed of beryllium aluminum silicate and is the chief ore of the element beryllium. Crystals of beryl in certain unique rocks called pegmatites can be as large as railroad boxcars. These immense crystals are never transparent, but some pegmatites contain smaller, well formed and transparent beryl crystals; these occur in various colors, and each variety used as a gemstone has its own special name. The blue or blue-green variety is called aquamarine. Large fine aquamarines occur in Brazil, Nigeria, Madagascar and many other places. The hexagonal (6-sided) symmetry of the mineral is evident in this crystal from Brazil.