Strontium

Strontium is best known for producing the brilliant crimson-red colour in fireworks and emergency flares. But it also played a sobering role in the Cold War: the radioactive isotope strontium-90, produced by nuclear weapons tests, was detected in children's teeth worldwide in the 1950s, helping drive public pressure for a nuclear test ban treaty.

  • Atomic Number3838 protons, 38 electrons
  • Atomic Mass87.62 uAbout 88× heavier than hydrogen
  • State at Room TempSolidsoft, silver-yellow metal
  • Density2.64 g/cm³About 2.6× denser than water
  • Melting / Boiling776.9°C / 1381.8°CMelts at 777°C
  • Discovered1790Adair Crawford, 1790

Strontium in Group 2: the alkaline earth metals.

Each alkaline earth metal is significantly heavier than the one above.

Atomic Mass Comparison
Calcium40 u
Strontium87.6 u
Barium137 u
Iron55.8 u
Radium226 u

Strontium (87.6 u) is just over twice the mass of calcium (40 u) and about two thirds the mass of barium (137 u). All alkaline earth metals give away their two outer electrons readily, but strontium's larger atoms make it more reactive than calcium but less than barium.

What is strontium?

Strontium is an alkaline earth metal in Group 2 of the periodic table, sitting below calcium. It has 38 protons and two electrons in its outer shell, which it readily gives away. Pure strontium is a soft, silver-yellow metal that reacts quickly with air (tarnishing immediately) and with water (more vigorously than calcium but less so than barium). Its chemistry closely resembles calcium's, and the two elements behave so similarly in biological systems that the body cannot always tell them apart.

Strontium gets its name from Strontian, a small village in Argyllshire in the Scottish Highlands, where strontianite, a strontium carbonate mineral, was first found in lead mines in the 1780s. The element was isolated from this mineral by the English chemist Humphry Davy in 1808, using electrolysis: the same technique he used for calcium, magnesium and barium in the same productive year.

Fact The radioactive isotope strontium-90, released by nuclear weapons tests during the Cold War, was taken up by plants, eaten by cows, concentrated in milk and deposited in children's growing bones and teeth. When surveys in the late 1950s found strontium-90 in children's baby teeth worldwide, it created huge public pressure for the 1963 Partial Nuclear Test Ban Treaty, which ended atmospheric nuclear weapons testing.

Where you find strontium

On Earth

Strontium is the 15th most abundant element in the Earth's crust at approx. 370 parts per million, relatively common, though never found as a free metal.

  • Celestite (SrSO₄). Strontium sulfate is the main commercial ore of strontium. Large deposits exist in China, Spain, Mexico, Turkey and Morocco.
  • Strontianite (SrCO₃). Strontium carbonate mineral, found in Scotland (where strontium was first identified) and in other locations worldwide.

How we use strontium

  • Fireworks and flares. Strontium salts (particularly strontium nitrate) burn with a brilliant crimson-red flame. Almost every red firework, signal flare and emergency flare owes its colour to strontium.
  • Ferrite magnets. Strontium ferrite (SrFe₁₂O₁₉) is the cheap magnetic material used in fridge magnets, electric motors in household appliances, and loudspeaker magnets.
  • Cathode ray tubes (historical). Strontium oxide was added to the glass of old TV screens to absorb X-rays produced by the electron beam and prevent them reaching viewers. Digital screens have made this use obsolete.
  • Medicine. Strontium ranelate was used to treat osteoporosis, because the body incorporates strontium into bone in place of calcium. Strontium-89 is used in treating bone cancer pain.
Did you know? The element strontium is named after the tiny village of Strontian in the Scottish Highlands, making it one of very few elements named after a specific small town. Strontian has a population of under 700 people. Locals are justifiably proud that their village gave its name to a chemical element used in fireworks around the world.

How it was discovered

Strontium was first identified as a new element in 1790 by the Irish chemist Adair Crawford, who noticed that a mineral from Strontian, Scotland, behaved differently from both barytes (barium sulfate) and other calcium minerals. He concluded it must contain a new alkaline earth. The element was officially confirmed and isolated by Humphry Davy in 1808, using electrolysis: the same technique he used for calcium in the same year. The discovery came during an extraordinarily productive period in Davy's career.

Deeper dive: radioactive strontium-90 and the Nuclear Test Ban Treaty

Strontium-90 is a radioactive isotope produced in large quantities by nuclear fission in reactors and weapons. It has a half-life of approx. 29 years. Because strontium chemistry so closely resembles calcium, the body incorporates strontium-90 into bones and teeth in place of calcium. Once there, the ongoing radioactive decay damages the surrounding bone marrow and tissue, potentially causing leukaemia and other cancers.

Atmospheric nuclear weapons tests during the 1950s and early 1960s released enormous quantities of strontium-90 into the atmosphere. It fell worldwide as radioactive fallout, was taken up by grass, eaten by cows and concentrated in milk. Baby Tooth Survey (1958-1961), a public health study in the USA that collected over 320,000 children's baby teeth and measured strontium-90 levels, provided dramatic evidence that nuclear testing was affecting children globally. This evidence was crucial in building public support for the 1963 Partial Nuclear Test Ban Treaty signed by the USA, USSR and UK, which ended atmospheric nuclear testing.

Strontium-87 is the stable end product of rubidium-87 decay and is used in rubidium-strontium radiometric dating to determine the ages of ancient igneous rocks. By measuring the current ratio of strontium-87 to the original strontium-86 (which does not change), geologists can calculate how long ago a rock crystallised, up to billions of years ago.

Strontium is the alkaline earth metal that colours fireworks red and played a pivotal role in ending atmospheric nuclear weapons testing. Moving to 39 protons brings us to yttrium, a transition metal named after a village in Sweden and critical for modern display technology.