Beryllium, a grayish-white metallic chemical element, formerly called glucinum, or glucinium. Beryllium is hard, brittle, lightweight, nonmagnetic, and an excellent conductor of heat. It is easily attacked by alkalis or mineral acids with the exception of nitric acid. When exposed to air at ordinary temperatures, the metal forms an oxide coating that protects it from rust. Beryllium is widely used in alloys, especially for imparting hardness and strength to copper. Beryllium-copper alloys are used to make electrical contacts, springs, nonsparking and antimagnetic tools, marine propellers, and many other devices.

Beryllium and many beryllium compounds are toxic. Beryllium metal, which is about two-thirds as heavy as aluminum, is used in structural parts of jet engines, missiles, high-speed aircraft, and spacecraft. It is used as an additive in solid rocket fuels and as a reflector to regulate the flow of neutrons in nuclear reactors. Because it is highly transparent to X rays, the metal is used in X-ray tubes to form a window" through which the rays are emitted.

The most important beryllium compound is beryllium oxide, or beryllia. It is extremely hard, it is strong, and it has high electrical resistance. Beryllium oxide is used as a heat-conducting material in electronic devices, as insulation for electric cable, and to produce high-temperature crucibles. It is also used in structural parts of nuclear reactors and missiles.

The most important beryllium ores are beryl and bertrandite. Bertrandite is the principal beryllium ore mined in the United States; beryl is mined in the rest of the world. Most beryllium is produced by converting the beryllium compounds in the ores to beryllium fluoride, and then reducing the fluoride with magnesium.

Beryllium was discovered in 1798 by the French chemist Louis Vauquelin. The metal was first prepared in pure form in 1828 by the German chemist Friedrich Whler and, independently, the French chemist Antoine Bussy.

Symbol: Be. Atomic number: 4. Atomic weight: 9.01218. Melting point: 2,332 F. (1,278 C.). Boiling point: 5,378 F. (2,970 C.). Specific gravity: 1.85. Beryllium has one stable isotope, Be-9. It belongs to Group II-A of the Periodic Table and has a valence of 2.