Cobalt (Co)

Cobalt (symbol Co) is the chemical element with atomic number 27: a transition metal, solid at 0 °C, with an atomic mass of 58.933 u. Discovered in 1735 (Georg Brandt).

Cobalt is a hard, magnetic metal, known for thousands of years for the intense blue it gives glass and ceramics. Today it is strategic for lithium-ion batteries and aircraft engines. Its production, concentrated in the Democratic Republic of the Congo, raises ethical questions. It also sits at the center of vitamin B12.

Key facts

Atomic number: 27
Symbol: Co
French name: Cobalt
Atomic mass: 58.933 u
Molar mass: 58.933 g/mol
Family: Transition metals
Position: period 4, group 9, d-block
State at 0 °C: Solid
Melting point: 1,494.9 °C
Boiling point: 2,926.9 °C
Density: 8.9 g/cm³
Electronegativity (Pauling): 1.88
First ionization energy: 760 kJ/mol
Atomic radius: 135 pm
Electron configuration: [Ar] 3d⁷ 4s²
Abundance in Earth's crust: 25 ppm (30th most abundant element)
Indicative price: 33 $/kg (order of magnitude)
Radioactive: no
Discovery: 1735, Georg Brandt

Origin of the name

From the German Kobold, a mischievous goblin of the mines.

What does cobalt look like?

A hard, shiny, magnetic metal, silvery-gray with a faint bluish tint.

Where is cobalt found?

About 25 ppm of Earth's crust. It is almost always associated with copper and nickel, and is usually a by-product of them, notably in Central Africa's Copperbelt.

Natural sources

Cobaltite
Carrollite
Heterogenite
Skutterudite
Erythrite

How is cobalt produced?

It is recovered when processing copper and nickel ores, by roasting, leaching (dissolving in acid) and then electrolysis or precipitation. Mine production exceeds 200,000 tonnes a year, about three quarters of it in the DR Congo, and much of it is refined in China.

Top producers

Democratic Republic of the Congo
Indonesia
Russia
Australia

What is cobalt used for?

Lithium-ion battery cathodes.
Superalloys for aircraft turbines.
Permanent magnets (samarium-cobalt, AlNiCo).
Blue pigment for glass, ceramics and paints.
Cobalt-60 for radiotherapy and sterilization.
Oil-refining catalysts.

In everyday life

The battery in your phone
Blue-patterned tableware
Very hard drill bits and cutting tools
Vitamin B12 in supplements

Role in living things

Essential as vitamin B12 (cobalamin), the only vitamin that contains a metal, vital for making red blood cells and for the nervous system. Humans cannot make it: it is produced by bacteria and comes from animal-based foods.

Hazards of cobalt

Cobalt dust irritates the lungs and causes skin allergies; some compounds are classified as possible carcinogens. Artisanal mining in the DR Congo exposes miners, including children, to dangerous conditions.

Cosmic origin

Supernovae: Forged in the cores of massive stars, then scattered when they explode.
White dwarfs: Produced by the thermonuclear explosion of a white dwarf (type Ia supernova).

History of cobalt

German miners used the word kobold, “mischievous goblin,” for an ore that looked like silver ore but yielded none and gave off toxic arsenic fumes. Around 1735, Swedish chemist Georg Brandt showed that the blue color of glass came from a new metal, cobalt: the first metal since antiquity discovered by a known individual.

Did you know?

The blue of Chinese Ming porcelain comes from cobalt oxide, sometimes imported from Persia.
In the 1960s, cobalt added to beer to stabilize the foam caused heart failure in heavy drinkers in Quebec.
Cobalt is one of only three metals that are ferromagnetic at room temperature, along with iron and nickel.

Isotopes of cobalt

A single stable isotope, cobalt-59. Cobalt-60, a powerful gamma emitter, sterilizes medical equipment and was long used in radiotherapy.

cobalt-57: radioactive, half-life 272 days. Source for Mössbauer spectroscopy and for calibrating gamma cameras.
cobalt-58: radioactive, half-life 70.9 days. Tracer of vitamin B12 absorption (the Schilling test).
cobalt-59: 100% of natural cobalt, stable
cobalt-60: radioactive, half-life 5.27 years. Sterilizing medical equipment and food, radiotherapy (the “cobalt bomb”) and industrial gamma radiography.

Common compounds

Lithium cobalt oxide (LiCoO₂)

Related elements

Same family (transition metals): Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Nickel (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Gold (Au), Mercury (Hg), Rutherfordium (Rf), Dubnium (Db), Seaborgium (Sg), Bohrium (Bh), Hassium (Hs).

Same column (group 9): Rhodium (Rh), Iridium (Ir), Meitnerium (Mt).