Beryllium was identified in 1798 by Louis-Nicolas Vauquelin, who found a new earth common to both beryl and emerald; the metal was isolated independently in 1828 by Friedrich Wohler and Antoine Bussy. Its name derives from beryl, the gemstone (Greek beryllos), the mineral in which it hides. For much of the nineteenth century it bore an alternative name, glucinium, from the Greek glykys, sweet, because its salts taste sweet, a property no longer tested for since beryllium and its compounds are severely toxic. It is a light, stiff, steel-grey metal transparent to X-rays.
Rare in the crust and difficult to work, it is used in springy copper-beryllium alloys, in aerospace parts and in the windows of X-ray tubes, but its dust and fumes are hazardous, causing the chronic lung disease known as berylliosis. Beryllium played a pivotal role in nuclear physics: bombarded with alpha particles in 1932, it released a neutral radiation that James Chadwick identified as the neutron, the discovery that completed the basic model of the atomic nucleus. The same reaction later made beryllium the standard neutron-source material paired with radioactive elements such as radium and polonium, and beryllium components still serve as neutron reflectors in nuclear reactors and weapons.