Tellurium · element 52
Rarer than platinum in the crust, yet it powers solar farms and once got mistaken for worthless rock
Key facts
Tellurium is one of the least common stable elements on Earth. If you sifted a tonne of average crust you would find only about a milligram of it, roughly the same as platinum. Yet this obscure metalloid has become quietly important, because a compound of it converts sunlight into electricity in one of the most widely deployed types of thin-film solar panel.
It is a grey, brittle, semi-metallic solid, chemically related to sulfur and selenium above it in the table. Its most notorious property is what it does to people: a trace of it in the body produces a garlic-like odour on the breath that can last for weeks.
Where it is found
Tellurium is rare partly because of Earth's history. It readily forms volatile compounds with hydrogen, and much of the tellurium present when the planet formed is thought to have been lost to space or drawn into the metallic core alongside iron. In the universe as a whole it is far more abundant than its crustal figure suggests.
On Earth it occurs mainly in gold and silver telluride minerals such as calaverite, and in copper sulfide ores. Almost no mine extracts tellurium as its main product. Instead it is recovered from the sludge that gathers at the anodes during electrolytic refining of copper. China, Russia, Japan, Canada and Sweden are among the main producers, and total world output is measured in hundreds of tonnes a year.
How it was discovered
In 1782 Franz-Joseph Müller von Reichenstein, chief inspector of mines in Transylvania, was studying a gold ore from Zlatna that he suspected contained antimony or bismuth. It did not behave like either. After years of tests he concluded it held a new metal, but he could not fully confirm it and his results were published in an obscure journal.
Sixteen years later Martin Heinrich Klaproth in Berlin obtained a sample, confirmed the discovery, and gave the element its name, from the Latin tellus, meaning Earth. Klaproth was careful to credit Müller. It was a fitting pairing, since Klaproth had also proposed the name uranium, after the planet Uranus, for a metal he found in 1789.
What we use it for
Cadmium telluride solar cells are the biggest single use. A layer of the compound only a few micrometres thick absorbs sunlight efficiently, and panels based on it are made at large scale for utility solar farms. Tellurium supply is one of the factors that limits how far this technology can grow.
Tellurium also does several smaller jobs. Bismuth telluride is the standard material in thermoelectric devices, which turn a temperature difference into electricity or, run backwards, act as small solid-state coolers in camping fridges and laser systems. Alloys of germanium, antimony and tellurium change between glassy and crystalline forms when heated, which was the basis of rewritable CDs and DVDs and some forms of computer memory. Small additions of tellurium make steel and copper easier to machine, and tellurium compounds are used to vulcanise rubber and tint glass.
Reading the numbers
Tellurium melts at about 450 °C and boils at about 988 °C. Both are low for an element that looks metallic, and are in line with a metalloid whose atoms are bound in chains rather than a fully metallic lattice. Its density of 6.24 grams per cubic centimetre makes it lighter than iron and a little over six times as dense as water.
The configuration [Kr] 4d10 5s2 5p4 puts tellurium in group 16, the oxygen family, below selenium and above polonium. With six outer electrons it can gain two to complete its shell, forming telluride ions, or share electrons to reach the +4 and +6 states, just as sulfur does. Its electronegativity of 2.1 and a high electron affinity of 190 kilojoules per mole confirm this non-metallic streak, even though its appearance is metallic. Tellurium is one of the clearest examples of why the metal and non-metal labels blur along the diagonal band of metalloids.
Safety and the environment
Tellurium and its compounds are toxic, though people rarely encounter them. The body converts even tiny amounts into dimethyl telluride, which is exhaled and gives a persistent garlic smell to breath and sweat. Higher exposures cause nausea, drowsiness and a metallic taste. Workers in copper refineries and electronics plants are the main group at risk.
Environmentally tellurium is so scarce that widespread contamination is not a concern. The main issue is at the end of a solar panel's life: cadmium telluride modules must be collected and recycled so that neither cadmium nor tellurium ends up in landfill, and manufacturers run take-back schemes for this reason.
Did you know?
- Exposure to a tiny amount of tellurium gives a person garlic-smelling breath that can persist for weeks.
- Tellurium is roughly as rare in the Earth's crust as platinum, but far more common in the universe as a whole.
- During the Kalgoorlie gold rush in Australia, miners discarded a grey mineral as waste before realising it was calaverite, a gold telluride rich in gold.
- The name tellurium comes from the Latin word for Earth, and the chemist who named it, Klaproth, had earlier named uranium after a planet.
- Rewritable DVDs stored data in a tellurium alloy that switches between a glassy and a crystalline state when heated by a laser.
More in the metalloids
The nearest neighbours of tellurium in the family, by atomic number.
See all 7 metalloids on one page, or browse all 118 elements.
Frequently asked questions
What is tellurium used for?
Its biggest use is in cadmium telluride thin-film solar panels. It is also the key ingredient in bismuth telluride thermoelectric coolers and generators, was used in rewritable optical discs, and is added in small amounts to steel and copper to make them easier to machine.
Is tellurium rare?
Yes, it is one of the rarest stable elements in the Earth's crust, at around one part per billion, similar to platinum. It is thought to have been lost from the crust early in Earth's history because it forms volatile compounds. Almost all of it is recovered as a by-product of copper refining.
Is tellurium toxic?
It is, though exposure is uncommon. Even small doses are converted by the body into dimethyl telluride, causing a strong garlic odour on the breath that can last weeks, and larger doses cause nausea and drowsiness. Workers handling it use gloves and ventilation.
Is tellurium a metal or a non-metal?
It is a metalloid, sitting between the two. Tellurium looks silvery and metallic, but it is brittle, a poor conductor, and forms compounds like its non-metal relatives sulfur and selenium. It behaves as a semiconductor rather than a true metal.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Tellurium reference article. Spotted an error? Tell us.