Beryllium crystal. Coloured scanning electron micrograph (SEM) of cleavage in a beryllium crystal. Beryllium (symbol Be) is an element of group 2A of the periodic table. Cleavage is the splitting, or tendency of a crystal to split, along definite crystalline planes (vertical and diagonal lines) to produce a smooth surface. Beryllium is used in alloys, as a light structural material and in nuclear reactors as a reflector or moderator. This beryllium crystal contains 2. 25 mole percent of copper. Magnification: x126 at 6x7cm size.