Strontium

Category: alkaline earth metal Atomic number: 38 Colour: silvery grey Melting point: 777°C (1,431°F) Boiling point: 1,377°C (2,511°F) First identified: 1790

In the late eighteenth century, a strange rock was discovered in a lead mine near the village of Strontian, on the shores of Loch Sunart, in Scotland’s western highlands. It was sent to Edinburgh for analysis, where the scientist Thomas Charles Hope proved it must contain a new element and commented on the fact that it causes a candle’s flame to burn red. (Strontium, as it was named, was isolated by Humphry Davy in 1808.)

It is in the form of red flames that you are most likely to be familiar with the element – the red flares often seen at football stadiums are coloured using it, as are red fireworks. As a metal, it is similar to the other elements of group 2, including beryllium, magnesium and calcium: it is soft and reacts easily to form oxides. And it is only found in the form of mineral compounds – one of these is celestite (strontium sulphate), which was discovered in England’s West Country in the eighteenth century (where it was being put to good use by local villagers as an ornamental gravel for their garden paths).

The radioactive isotope strontium-90 was produced by nuclear tests from 1945 onwards – it is a problematic isotope, as it can be absorbed into the food chain via grassland and dairy products, and our bodies mistake it for calcium, collecting it in bones and teeth. It is one of the harmful substances that was released in the 1986 Chernobyl accident and spread across parts of Russia and Europe.

Strontium’s similarity to calcium has also led to its positive medical uses: in cancer therapy it is used as a radioactive tracer (allowing doctors to track cell movements and other processes in the body), and the non-radioactive salt, strontium ranelate, can be used to treat osteoporosis, as it slows the breakdown of old bone tissue and stimulates new bone production.