Cobalt

Cobalt is the element that gives medieval cathedral windows and the finest Chinese porcelain their striking deep blue colour. Today it is best known as a critical component of lithium-ion batteries, putting it inside almost every smartphone, laptop and electric car on the planet.

  • Atomic Number2727 protons, 27 electrons
  • Atomic Mass58.93319 uAbout 59× heavier than hydrogen
  • State at Room TempSolidhard, lustrous silver-blue metal
  • Density8.86 g/cm³Similar density to iron
  • Melting / Boiling1494.8°C / 2926.8°CMelts at 1,495°C
  • Discovered1735Georg Brandt, 1735

Where does cobalt sit among the iron group metals?

Cobalt, iron and nickel are the three classic magnetic transition metals of Period 4.

Atomic Mass Comparison
Iron55.8 u
Cobalt58.9 u
Nickel58.7 u
Copper63.5 u
Zinc65.4 u

Cobalt (58.9 u) sits almost exactly between iron (55.8 u) and nickel (58.7 u) in mass. These three elements form a trio of naturally magnetic metals and are found together in many ores and meteorites.

What is cobalt?

Cobalt is a transition metal in Group 9 of the periodic table. It has 27 protons and is one of only three naturally magnetic elements at room temperature (alongside iron and nickel). Its most common oxidation states are +2 and +3. Cobalt compounds are typically vivid shades of blue or pink, which has made them prized as pigments for thousands of years. The metal itself is hard, lustrous and corrosion-resistant.

Cobalt gets its name from the German word Kobold, meaning goblin or mischievous spirit. German miners in the 16th century cursed cobalt-bearing ores because they looked like silver-containing ores but yielded no silver, worse, smelting them produced toxic arsenic oxide fumes. They blamed the goblins of the mines. The element was identified as a new substance in 1735 by the Swedish chemist Georg Brandt, who showed the blue colour of certain glass came from cobalt, not bismuth as had been believed.

Fact The striking blue of ancient Egyptian glass and the deep blue of Chinese Tang dynasty porcelain both come from cobalt. Egyptian blue: one of the world's oldest synthetic pigments, made as early as 3000 BCE, contains cobalt compounds. The Egyptians sourced their cobalt from oases in the Egyptian desert, where cobalt-bearing minerals occurred near the surface.

Where you find cobalt

On Earth

Cobalt is found in the Earth's crust at approx. 25 parts per million, almost always combined with arsenic, sulfur or other metals rather than as a free element.

  • Cobaltite and smaltite. Arsenic-containing cobalt minerals found in various countries, including the Democratic Republic of Congo (DRC), which holds approx. 70% of the world's cobalt reserves.
  • By-product of nickel and copper mining. Most commercial cobalt is recovered as a by-product of nickel and copper smelting rather than from dedicated cobalt mines.

How we use cobalt

  • Lithium-ion batteries. Cobalt is a key component of the positive electrode (cathode) in most lithium-ion batteries. A typical smartphone battery contains 5 to 10 grams of cobalt; an electric car battery may contain over 10 kilograms.
  • Superalloys. Cobalt alloys retain their strength at very high temperatures and are used in jet engine turbine blades, which operate in gases hotter than the melting point of most metals.
  • Blue pigments. Cobalt blue (cobalt aluminate) is a brilliant, stable blue pigment used by artists since the 19th century. It is the paint colour often called "cerulean blue".
  • Medicine (cobalt-60). Radioactive cobalt-60 is used in radiotherapy to treat cancer, directing gamma rays precisely at tumours. It is also used to sterilise medical equipment.
Did you know? Vitamin B12, essential for nerve function and producing red blood cells, is the only vitamin that contains a metal atom. At its core is a cobalt atom bonded to a ring of nitrogen atoms in a structure called a corrin ring. Without cobalt, vitamin B12 cannot exist, and without vitamin B12, neurons and blood cells suffer. Vegans are advised to supplement B12 because the vitamin is mainly found in animal products.

How it was discovered

Cobalt was the first metal to be discovered since antiquity. In 1735, the Swedish chemist Georg Brandt proved that the blue colour of glass was caused by a new, previously unrecognised metal, not bismuth, as had been assumed. He isolated an impure sample and established its properties. His identification of cobalt was initially contested by other chemists but was ultimately vindicated, establishing Brandt as the discoverer of the eighth known metal.

Deeper dive: cobalt in batteries and the Congo's cobalt dilemma

Cobalt's role in rechargeable batteries stems from its ability to cycle reversibly between oxidation states (+3 to +4) as the battery charges and discharges. In lithium cobalt oxide (LiCoO₂) cathodes, lithium ions are extracted during charging and re-inserted during discharge, with cobalt ions changing oxidation state to compensate. This process can be repeated thousands of times. Cobalt makes the cathode thermally stable, without it, some battery chemistries can overheat and cause fires.

The concentration of cobalt reserves in the Democratic Republic of Congo, approx. 70% of global supply, creates major geopolitical and ethical concerns. Much of the DRC's cobalt is mined in small-scale "artisanal" mines with poor safety standards, child labour and severe environmental damage. This has driven intensive research into cobalt-free or cobalt-reduced battery chemistries, such as lithium iron phosphate (LFP) batteries now used in some electric vehicles.

Cobalt-60, produced in nuclear reactors, emits powerful gamma rays and has a half-life of approx. 5.27 years. It is used in cancer radiotherapy (particularly for cervical and head and neck cancers), industrial radiography (checking welds in pipelines), and food irradiation (to kill bacteria without heating). It is one of the most medically important radioactive isotopes.

Cobalt is the element of blue pigments and rechargeable batteries. Moving to 28 protons brings us to nickel, a corrosion-resistant metal inside coins, batteries and countless alloys.