Beryllium

Beryllium (pronounced /bəˈrɪliəm/) is a chemical element with the symbol Be and atomic number 4. A bivalent element, beryllium is a steel grey, strong, light-weight yet brittle, alkaline earth metal. It is primarily used as a hardening agent in alloys, most notably beryllium copper. Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts.

Beryllium is relatively rare element in both the Earth and the universe, due to the fact that it is not formed in conventional stellar nucleosynthesis. The element is not known to be necessary or useful for either plant or animal life.

The material is used by the Covenant in their ships, notably in their holographic projectors