beryllium
/bəˈrɪljəm/noun
mass noun
- the chemical element of atomic number 4, a hard grey metal. (Symbol: Be)（化学元素）铍（符号： Be）。
Beryllium is the lightest of the alkaline earth metals, and its chief source is the mineral beryl. It is used in the manufacture of light corrosion-resistant alloys and in windows in X-ray equipment.