Beryllium is a chemical element, typically found as a solid in its elemental form. It has the chemical symbol Be, atomic number (number of protons) Z = 4, and a standard atomic weight of 9.012182 g/mol.
Beryllium is considered to be a member of the "Alkaline Earth Metal" class of elements. At a pressure of 101.325 kPa, it has a boiling point of 2471 °C, and a melting point of 1287 °C. Its density is 1.85 g/cc.
Beryllium is toxic to living organisms.
It is a strategic material in nuclear weapons, specifically acting as a neutron reflector surrounding the fission core, increasing its neutron density, and decreasing the size of the device. A beryllium reflector was first used operationally in the U.S. Mark 12 (nuclear weapon),