Gallium is considered a technology-critical element by the United States National Library of Medicine and Frontiers Media.

Gallium(III) behaves in a similar manner to ferric salts in biological systems and has been used in some medical applications, including pharmaceuticals and radiopharmaceuticals.

Gallium shares the higher-density liquid state with a short list of other materials that includes water, silicon, germanium, bismuth, and plutonium.

Gallium is one of the four non-radioactive metals (with caesium, rubidium, and mercury) that are known to be liquid at, or near, normal room temperature.

It is also notable for having one of the largest liquid ranges for a metal, and for having (unlike mercury) a low vapor pressure at high temperatures.

[17]: 224  Unlike mercury, liquid gallium metal wets glass and skin, along with most other materials (with the exceptions of quartz, graphite, gallium(III) oxide[25] and PTFE),[17]: 221  making it mechanically more difficult to handle even though it is substantially less toxic and requires far fewer precautions than mercury.

At room temperature, gallium metal is not reactive with air and water because it forms a passive, protective oxide layer.

[33]: 162  Alternatively, Ga(OH)3 can be used at 747 °C:[38] Reacting a mixture of alkali metal carbonates and Ga2O3 with H2S leads to the formation of thiogallates containing the [Ga2S4]2− anion.

[32]: 1034  GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony.

Its structure is similar to diborane, having two hydrogen atoms bridging the two gallium centers,[32]: 1031  unlike α-AlH3 in which aluminium has a coordination number of 6.

Triphenylgallium is monomeric in solution, but its crystals form chain structures due to weak intermolecluar Ga···C interactions.

[17]: 262–5 In 1871, the existence of gallium was first predicted by Russian chemist Dmitri Mendeleev, who named it "eka-aluminium" from its position in his periodic table.

[17]: 217 Gallium was discovered using spectroscopy by French chemist Paul-Émile Lecoq de Boisbaudran in 1875 from its characteristic spectrum (two violet lines) in a sample of sphalerite.

It was later claimed that, in a multilingual pun of a kind favoured by men of science in the 19th century, he had also named gallium after himself: Le coq is French for 'the rooster', and the Latin word for 'rooster' is gallus.

[17]: 217 From its discovery in 1875 until the era of semiconductors, the primary uses of gallium were high-temperature thermometrics and metal alloys with unusual properties of stability or ease of melting (some such being liquid at room temperature).

[54] Gallium does not exist as a free element in the Earth's crust, and the few high-content minerals, such as gallite (CuGaS2), are too rare to serve as a primary source.

[55] The United States Geological Survey (USGS) estimates that more than 1 million tons of gallium is contained in known reserves of bauxite and zinc ores.

[65] Its by-product status means that gallium production is constrained by the amount of bauxite, sulfidic zinc ores (and coal) extracted per year.

The supply potential of a by-product is defined as that amount which is economically extractable from its host materials per year under current market conditions (i.e. technology and price).

China, Japan, South Korea, Russia, and Ukraine were the leading producers, while Germany ceased primary production of gallium in 2016.

[65] It amounted to $7.5 billion in 2016, with 53% originating from cell phones, 27% from wireless communications, and the rest from automotive, consumer, fiber-optic, and military applications.

[74] Other major applications of gallium nitride are cable television transmission, commercial wireless infrastructure, power electronics, and satellites.

[87][88] The plutonium used in nuclear weapon pits is stabilized in the δ phase and made machinable by alloying with gallium.

Because these processes include inflammation, a marker for many disease states, several gallium salts are used (or are in development) as pharmaceuticals and radiopharmaceuticals in medicine.

Interest in the anticancer properties of gallium emerged when it was discovered that 67Ga(III) citrate injected in tumor-bearing animals localized to sites of tumor.

Clinical trials have shown gallium nitrate to have antineoplastic activity against non-Hodgkin's lymphoma and urothelial cancers.

[91] Gallium nitrate (brand name Ganite) has been used as an intravenous pharmaceutical to treat hypercalcemia associated with tumor metastasis to bones.

[94][95] A complex amine-phenol Ga(III) compound MR045 is selectively toxic to parasites resistant to chloroquine, a common drug against malaria.

Both the Ga(III) complex and chloroquine act by inhibiting crystallization of hemozoin, a disposal product formed from the digestion of blood by the parasites.

For example, a focused gallium-ion beam was used to create the world's smallest book, Teeny Ted from Turnip Town.