Germanium · element 32
The semiconductor that started the transistor age, now guiding light through the world's fibre optic cables
Key facts
The very first transistor, built at Bell Laboratories in December 1947, was a sliver of germanium with two gold contacts pressed against it. For a decade germanium was the material of the electronics revolution, until silicon proved cheaper and more forgiving of heat. Germanium never went away. Today it bends infrared light in thermal cameras, raises the refractive index inside optical fibres, and forms the base layer of the solar cells that power satellites.
Germanium is a metalloid: hard, brittle, greyish-white and shiny like a metal, but a poor conductor unless it is warmed or doped with impurities. It sits in group 14 between silicon and tin, and its chemistry is a close copy of silicon's.
Where it is found
Germanium is scattered through the crust at only a few parts per million and rarely gathers into minerals of its own. Argyrodite and germanite exist but are too rare to mine. Instead, germanium is carried along with zinc, substituting for zinc in the sulfide mineral sphalerite, and it is concentrated in certain coals.
Most primary germanium is recovered from the flue dusts and residues of zinc smelters. Some coal-fired power stations in China and Russia burn coal rich enough in germanium that the ash is worth processing. China dominates supply. Because optical parts and semiconductor wafers can be reclaimed, recycling provides a meaningful share of what the industry uses.
How it was discovered
In 1885 a new silver mineral, argyrodite, was found in the Himmelsfürst mine near Freiberg in Saxony. Clemens Winkler, a chemist at the local mining academy, analysed it the following year and found that about seven per cent of the mass could not be accounted for by any known element. He tracked down the missing portion and isolated a new element in February 1886.
Winkler first considered calling it neptunium, but settled on germanium in honour of his country. Mendeleev had predicted a missing element beneath silicon, eka-silicon, with an atomic weight near 72 and a density around 5.5. Winkler's measurements matched closely, and germanium joined gallium and scandium as the three elements whose discovery confirmed the periodic table.
What we use it for
The largest use today is in optics. The core of a glass optical fibre is doped with germanium dioxide to raise its refractive index, which is what keeps light trapped inside the fibre across oceans. Germanium is transparent to infrared light even though it looks like a metal, so it is machined into lenses and windows for thermal imaging cameras, night vision equipment and gas sensors.
In electronics, germanium is grown as a substrate for the multi-junction solar cells used on spacecraft, and silicon-germanium alloys speed up chips in radio and radar systems. Ultra-pure germanium crystals make the most precise detectors for gamma rays, used in physics laboratories and border security. Germanium compounds also serve as catalysts in making PET plastic, and some guitarists still hunt for vintage fuzz pedals built with germanium transistors because of their soft, warm distortion.
Reading the numbers
Germanium melts at 938 °C and boils at 2833 °C. Its density of 5.32 grams per cubic centimetre is a little over five times that of water and well below iron. Like silicon and water, it expands slightly as it solidifies, which matters when growing large single crystals.
The configuration [Ar] 3d10 4s2 4p2 gives four outer electrons, so germanium forms four covalent bonds and crystallises in the same diamond structure as silicon. The gap between its filled and empty electron bands is smaller than silicon's, which is why germanium transistors leaked current when warm and why silicon eventually won. Its electronegativity of 2.01 is slightly higher than both silicon and tin, a small zig-zag caused by the filled d shell pulling the outer electrons inward. The first ionisation energy of 762 kJ/mol sits neatly between gallium and arsenic.
Safety and the environment
Metallic germanium and its oxide are low in toxicity, and no biological role is known. The gas germane, GeH4, is toxic and flammable and is handled only in semiconductor plants with specialist equipment. Supplements containing germanium compounds have been sold as health products, and several cases of serious kidney damage have been linked to them. Health authorities advise against taking them.
Environmental impact is mostly tied to zinc mining and coal burning. Recovering germanium from fly ash and from scrap optics reduces the need for new extraction.
Did you know?
- The first working transistor, demonstrated at Bell Labs in December 1947, used a small block of germanium.
- Germanium looks like a shiny metal but is transparent to infrared light, so thermal camera lenses are made from it.
- Winkler discovered germanium by chasing down the seven per cent of a mineral's mass that no known element could explain.
- Germanium was one of three elements, with gallium and scandium, whose discovery matched Mendeleev's predictions and proved the periodic table worked.
- Some coal deposits contain enough germanium that the ash left after burning is refined to extract it.
- Ultra-pure germanium crystals are the detector of choice for identifying radioactive materials by their gamma rays.
More in the metalloids
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 7 metalloids on one page, or browse all 118 elements.
Compare Germanium with another element
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Frequently asked questions
Is germanium a metal?
Germanium is classed as a metalloid. It is shiny, hard and brittle like a metal, but it conducts electricity poorly at room temperature and forms covalent bonds like a non-metal. This in-between behaviour is exactly what makes it useful as a semiconductor.
Why did silicon replace germanium in electronics?
Silicon is far more abundant and cheaper, and its oxide forms an excellent natural insulating layer that made integrated circuits practical. Germanium transistors also became leaky at moderately high temperatures because of the smaller gap between its electron bands. Silicon devices tolerate heat better.
Are germanium supplements safe?
No. Germanium has no known nutritional role, and organic germanium supplements have been linked to kidney failure and other serious harm. Health agencies in several countries warn against taking them.
What is germanium used for today?
Its main uses are in fibre optic cables, infrared lenses for thermal imaging, and as a substrate for high-efficiency solar cells on satellites. It also appears in catalysts for PET plastic and in gamma ray detectors.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Germanium reference article. Spotted an error? Tell us.