Beryllium

Light, stiff and unforgiving

Beryllium is a hard, brittle, steel-grey metal. It is light — 1.85 g/cm³, a third less than aluminium — yet it melts at 1287 °C and is stiffer than steel, so stiff for its weight that sound travels through it faster than through any other metal. Its two electrons sit outside a helium core in the smallest atom of any metal, and X-rays pass through it almost as if it were not there. A thin skin of oxide protects it from air and water.

Its small, doubly charged ion holds electrons so tightly that beryllium behaves less like its heavier relatives magnesium and calcium than like aluminium, its diagonal neighbour: its compounds are largely covalent and its oxide dissolves in acids and alkalis alike. Its salts taste sweet, and its dust is dangerous: inhaled, even in small amounts, it can cause berylliosis, a slow scarring of the lungs, so the metal is machined behind extraction hoods.

It has a single stable isotope, ⁹Be. The next, ⁸Be, falls apart into two helium nuclei in less than 10⁻¹⁶ seconds, a fact that shapes the universe: it is the bottleneck through which stars must squeeze to make carbon.

Emeralds and a mountain in Utah

Beryllium is rare, about three parts per million of the crust, and it concentrates in a few minerals. The best known is beryl, Be₃Al₂Si₆O₁₈, which as a clear crystal is a gemstone: emerald when a trace of chromium turns it green, aquamarine when iron turns it blue. The ore that matters is humbler, bertrandite, a hydrated silicate mined at Spor Mountain in Utah, which supplies most of the world; China and Kazakhstan produce most of the rest, and the whole world's output is only a few hundred tonnes of metal a year.

The ore is broken down to beryllium hydroxide, converted to the fluoride and reduced with magnesium at about 1300 °C; the metal is then cast or, more often, pressed from powder and sintered.

Where nothing else will do

Most beryllium goes into copper. An alloy with about 2 % of it can be hardened to the strength of steel while keeping copper's conductivity, and it does not spark when struck: it makes springs, electrical contacts, aircraft bushings and the tools used around explosives. The pure metal is reserved for the extreme. It forms the eighteen mirror segments of the James Webb Space Telescope, coated with gold, chosen because it holds its shape at forty degrees above absolute zero; it makes the gyroscopes of guidance systems and the windows of X-ray tubes and detectors. In reactors and weapons it reflects and multiplies neutrons, and it was a beryllium target, struck by alpha particles, that gave James Chadwick the neutron itself in 1932. Beryllium oxide, unusually, conducts heat like a metal while insulating like a ceramic, and cools electronics.

Discovery and name

Emerald and beryl have been prized since antiquity, but nobody suspected a new element in them until 1798, when the mineralogist René Just Haüy noticed that the two had the same crystal form and asked Louis-Nicolas Vauquelin to compare them. Vauquelin found that both contained an unknown "earth" whose salts tasted sweet. The editors of the Annales de Chimie named it glucine, from the Greek glykys, sweet, and the element was glucinium in France for more than a century; Martin Klaproth objected that yttrium salts were sweet too, and proposed beryllium, after the stone.

The metal came in 1828, when Friedrich Wöhler in Berlin and Antoine Bussy in Paris independently reduced beryllium chloride with potassium and obtained a grey powder. Only in the middle of the twentieth century did beryllium become the one accepted name.