The lightest alkaline earth metal is beryllium (Be). It has an atomic number of 4 and a relative atomic mass of 9.0122. Beryllium is a hard, brittle metal with a silvery-white colour. It is the only alkaline earth metal that is not silver in colour. Beryllium is also the strongest of the alkaline earth metals and has a high melting point (1,287 °C) and a high boiling point (2,970 °C).