Chromium · element 24
The element that makes rubies red, emeralds green and stainless steel stainless
Key facts
Chromium takes its name from the Greek word for colour, and it deserves it. Traces of chromium make rubies red and emeralds green. Its compounds gave us the yellow of school buses and Van Gogh's sunflowers, the green of old wallpaper, and the orange of the potassium dichromate in a school lab. Yet the metal itself is grey, hard, and almost boringly resistant to tarnish.
That resistance is chromium's real gift. Mixed into iron it makes stainless steel, the material of cutlery, kitchen sinks, surgical instruments and chemical plant, and plated onto steel it gives the mirror shine of old car bumpers and modern bathroom taps.
Where it is found
The only commercially important ore is chromite, an oxide of iron and chromium. South Africa holds the largest reserves in the vast Bushveld igneous complex, with Kazakhstan, Turkey and India as other major producers. Chromite forms in layered igneous intrusions where dense crystals settled out of slowly cooling magma, building up bands that can be traced for many kilometres.
Small amounts of chromium are scattered through many rocks and minerals, which is how it ends up colouring gemstones. Crocoite, a brilliant orange-red lead chromate best known from Tasmania, is prized by collectors and was the mineral in which chromium was first identified. Traces of chromium(III) occur in the human body, and for years it was listed as an essential nutrient, though that status is now questioned.
How it was discovered
In 1797 Louis Nicolas Vauquelin in Paris analysed the striking red-orange mineral crocoite from Siberian mines. He dissolved it, removed the lead, and was left with the green oxide of a new metal. The following year he heated the oxide with charcoal and obtained the metal itself. He went on to show that the colour of emerald and ruby came from chromium. The name, from the Greek chroma, was suggested by colleagues struck by the range of colours his compounds produced. Industrial use had to wait more than a century. Rust-resisting chromium steels were developed by several groups in the early 1910s, with Harry Brearley in Sheffield credited with the cutlery steel of 1913 that became known as stainless.
What we use it for
The steel industry consumes most chromium. Stainless steel contains at least about 10.5 per cent chromium, which reacts with oxygen to form an invisible, self-healing oxide layer that stops rust from ever getting started. Higher chromium contents give steels that survive hot gases in turbines and furnaces. Chrome plating, a thin electroplated layer, provides decorative shine and hard, wear-resistant surfaces for hydraulic rams and engine parts.
Chromium compounds tan most of the world's leather, colour bricks, glass and paints, and in the past made yellow road markings and green pigments. Chromite is used in heat-resistant furnace bricks. Chromic acid and dichromates are strong oxidisers in laboratories and industry, though safer alternatives are steadily replacing them.
Reading the numbers
Chromium melts at about 1907 °C and boils at about 2671 °C. Its density of 7.19 g/cm³ is a little less than iron, so adding it to steel barely changes the weight. The configuration [Ar] 3d5 4s1 is unusual: you might expect 3d4 4s2, but a half-filled d shell of five electrons is especially stable, so one electron is promoted to achieve it. This gives chromium six potential outer electrons and oxidation states from +2 to +6. Chromium(III) is stable and usually green or violet; chromium(VI), in chromates and dichromates, is a powerful oxidiser and typically yellow or orange. The first ionisation energy of 653 kJ per mole is typical of the first row of transition metals. Chromium is among the hardest of all pure metals, and it sits in group 6 above molybdenum and tungsten, which share its hardness and its very high melting points.
Safety and the environment
The oxidation state matters enormously. Chromium(III), found in food and stainless steel, is harmless. Chromium(VI), in chromates and chromic acid, is a known cause of lung cancer when inhaled and produces skin ulcers and allergic dermatitis. Contamination of groundwater by chromium(VI) from plating and tanning plants has caused serious harm, and the case in Hinkley, California became famous through the film Erin Brockovich. Regulations in the European Union and elsewhere now restrict hexavalent chromium in electronics and consumer goods, and industry is shifting to trivalent plating processes and chromium-free leather tanning.
Did you know?
- The same element gives ruby its red and emerald its green: chromium atoms replacing aluminium in two different host crystals absorb light differently.
- Chromium is among the hardest pure metals and takes a high polish, which is why chrome plating is used both for decoration and for wear resistance.
- Chrome yellow, a lead chromate pigment, was the colour of American school buses and of several of Van Gogh's sunflower paintings, some of which have darkened as the pigment degraded.
- Chromium is the only element that is antiferromagnetic at room temperature, meaning its atomic magnets line up in alternating directions and cancel out.
- Stainless steel was developed as a rust-resistant gun barrel steel in Sheffield in 1913 before anyone thought to make knives from it.
- Vauquelin, who discovered chromium, also discovered beryllium the following year.
More in the transition metals
Column-mates come first, since elements in one column have outer electrons arranged in a similar way and tend to behave alike; the rest are the nearest neighbours in the family.
See all 38 transition metals on one page, or browse all 118 elements.
Compare Chromium with another element
Each comparison has a side-by-side data table and a plain-English summary of the differences.
Frequently asked questions
Is chromium toxic?
It depends entirely on its form. Chromium(III), the kind in stainless steel and food, is very low in toxicity. Chromium(VI) compounds such as chromates are carcinogenic when breathed in and can cause skin ulcers, so they are tightly regulated.
What is chromium used for?
Most goes into stainless and other alloy steels, where it prevents rust and adds hardness. It is also electroplated onto steel as chrome, used to tan leather, and made into pigments and refractory bricks.
Why does stainless steel not rust?
The chromium in it reacts with oxygen to form a very thin, transparent layer of chromium oxide over the surface. This layer seals the iron away from air and water, and if it is scratched it re-forms within moments.
Is chrome the same as chromium?
Chrome is simply the everyday name for a chromium coating. Chrome-plated parts are usually steel or plastic with a thin electroplated layer of chromium on top, often over layers of copper and nickel.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Chromium reference article. Spotted an error? Tell us.