Barium · element 56
The metal that lights fireworks green, weighs down oil wells, and shows up your insides on an X-ray
Key facts
Barium takes its name from the Greek word for heavy, which is a little unfair. The metal itself is only about three and a half times as dense as water, lighter than iron. The name really belongs to its minerals, which are so dense that miners once puzzled over the unusual weight of the pale stone they were digging out.
Most people meet barium in one of two places. In a hospital, a barium meal or enema coats the gut so that the digestive tract shows up clearly on an X-ray. In the night sky, barium salts give fireworks their vivid green. Behind the scenes it also plays a large role in drilling for oil and gas.
Where it is found
Barium is fairly common, around 400 parts per million of the crust, more abundant than copper or zinc. It is far too reactive to occur as a metal, so it is always found combined, mainly as barite, the sulfate, and less commonly as witherite, the carbonate. Barite forms in veins and sedimentary layers and is easily recognised by its weight.
China is the largest producer of barite by a wide margin, with India, Morocco, Mexico, Turkey and the United States also mining it. Almost all of this barite is used as it comes, ground into powder, rather than being turned into barium metal.
How it was discovered
The story starts in Bologna in the early 1600s, when a shoemaker and alchemist called Vincenzo Casciarolo found that a dense local stone, heated with charcoal, glowed in the dark after being exposed to sunlight. The Bologna stone became a famous curiosity and was eventually shown to be barite converted to barium sulfide.
In 1774 the Swedish chemist Carl Wilhelm Scheele showed that barite contained a new earth, an oxide that did not match lime or any other known substance. Barium metal itself was first isolated in 1808 by Humphry Davy in London, who used the newly invented electric battery to split barium salts, in the same series of experiments that gave the world calcium, strontium and magnesium.
What we use it for
By weight, the overwhelming use is drilling mud. When a well is drilled for oil or gas, a fluid is pumped down to cool the bit and carry rock chips back up. Finely ground barite is added to make the fluid dense enough to hold back the pressure of the gas and oil deep underground. This use consumes the large majority of barite mined.
Barium sulfate is also the contrast agent in medical imaging. It is opaque to X-rays and so insoluble that it passes through the body without being absorbed, which makes it safe to swallow. Barium nitrate and chlorate give green flames to fireworks and flares. Barium carbonate goes into glass, bricks and ceramic glazes, and barium titanate is a ceramic used in capacitors and sensors because of its strong electrical response.
Reading the numbers
Barium melts at about 727 °C and boils at about 1845 °C. With a density of 3.51 grams per cubic centimetre it is less than half as dense as iron and not far above aluminium, which shows that the heaviness in its name refers to its ores, not the metal.
Its configuration, [Xe] 6s2, gives two outer electrons, placing barium in group 2 with the alkaline earth metals below calcium and strontium. It gives up both electrons easily, with a first ionisation energy of 503 kilojoules per mole, forming the Ba2+ ion in virtually all its compounds. Its electronegativity of 0.89 is among the lowest in the table, barely above caesium next door. As the largest of the stable group 2 metals, barium is the most reactive of them, and the trend down the group from beryllium to barium is a textbook example of reactivity increasing with atomic size.
Safety and the environment
Barium's safety depends entirely on solubility. Barium sulfate is insoluble and harmless, which is why patients can swallow it. Soluble barium salts such as the chloride, nitrate and carbonate are poisonous, causing muscle weakness, heart rhythm disturbances and paralysis. Barium carbonate was once used as rat poison. The metal itself reacts with water and must be stored under oil.
Barium from barite is not a major environmental pollutant, but drilling fluids and mining waste can release soluble barium into groundwater, and some regions have naturally high barium in well water. Barium in fireworks contributes to the fine particle pollution that follows big displays.
Did you know?
- The Bologna stone, a barite mineral that glowed after exposure to sunlight, was one of the first known phosphorescent materials, described in the early seventeenth century.
- Barium's name means heavy, yet the metal is less than half as dense as iron.
- The green colour in fireworks almost always comes from barium compounds.
- Barium sulfate is so insoluble that patients can safely drink a thick suspension of it before an X-ray, even though soluble barium salts are poisonous.
- Most of the barite mined each year is simply ground into powder and pumped down oil and gas wells to weigh down drilling fluid.
More in the alkaline earth metals
These share a column with barium, so their outer electrons are arranged in a similar way and they tend to behave alike.
See all 6 alkaline earth metals on one page, or browse all 118 elements.
Frequently asked questions
Is barium safe to swallow?
Barium sulfate, the form used in a barium meal, is safe because it is so insoluble that almost none is absorbed and it passes straight through the gut. Soluble barium compounds such as barium chloride or carbonate are toxic and must never be swallowed. The difference lies entirely in solubility.
Why is barium used in X-rays?
Barium atoms are heavy and absorb X-rays strongly, so a thick suspension of barium sulfate coating the stomach or bowel shows up bright white on the image. This outlines the shape of the digestive tract and reveals ulcers, blockages or growths that soft tissue alone would not show.
What colour does barium burn?
Barium compounds burn with an apple-green flame. The colour comes from barium atoms and molecules emitting green light as their electrons drop back to lower energy levels, and it is the standard source of green in fireworks and signal flares.
Is barium a heavy metal?
Chemically it is often grouped with the toxic heavy metals because its soluble salts are poisonous, but physically it is not especially dense at 3.5 grams per cubic centimetre, less than half the density of iron. The name comes from the heaviness of its mineral barite rather than the metal itself.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Barium reference article. Spotted an error? Tell us.