Bill Hovey, of Alexandra, asks :-

Beryllium has many similarities to aluminium so why hasn't it come into general use?

Brian Robinson, a chemist at Otago University, responded.

Many of the properties of beryllium are similar to those of aluminium. Both have high melting temperatures, the same boiling point and similar electrical and hardness and reactivity in air.

Beryllium is much rarer in the Earth's crust so is much more expensive than aluminium. The total annual world production of beryllium is about 400 tonnes. The gemstone beryl consists of beryllium aluminium silicate. Emeralds and aquamarine are varieties of beryl.

The compounds of beryllium are extremely toxic, especially as dust and oxides, as it replaces magnesium in some important enzymes. The average 70kg human body contains about 36 millionths of a gramme of beryllium.

Beryllium is difficult to machine but it is very much lighter than aluminium so is used to produce high-strength, lightweight, alloys, for example in aerospace applications, non-sparking copper alloy tools for the petroleum industry and high temperature electrical connections. It is the first relatively non-reactive element in the periodic table and has only 4 electrons per atom. Because X-rays are scattered by electrons, the fewer electrons per atom the better the element transmits x-rays. Hence beryllium is used as the window material for X-ray tubes.

Neutrons have very little interaction with the nucleus of beryllium so it is used for making containers of fuel rods for nuclear-reactors.