Indium is a chemical element with atomic number 49 and the symbol In, placing it among the post-transition metals on the periodic table.

It belongs to group 13, where it sits between gallium above and thallium below, and shows properties that are intermediate between the two.

Indium was discovered in 1863 by German chemists Ferdinand Reich and Hieronymous Theodor Richter while analyzing mineral ores using spectroscopy.

Its discovery was confirmed when researchers observed an unusual bright indigo-blue spectral line that did not match any known element at the time.

The element was named “indium” after the indigo color seen in its spectral emission line, which inspired its Latin-based name. Indium was originally named using the Latin word “indicum,” meaning indigo, which also relates to its historical association with India-exported dye.

Hieronymous Theodor Richter succeeded in isolating indium metal in 1864, one year after its initial identification.

A 0.5 kg ingot of indium was later showcased at the 1867 World Fair, marking one of its earliest public presentations.

Indium is extremely soft, with a Mohs hardness of about 1.2, meaning it can be easily cut with a knife.

When rubbed on paper, indium can leave a visible mark similar to a pencil due to its softness and ductility.

It is so malleable that it can be bent and shaped easily, producing a faint crackling sound from crystal twinning.

Indium can wet glass surfaces, meaning it can spread across and adhere to glass instead of forming droplets.

It has a relatively low melting point of about 156.6 °C, allowing it to melt in very hot water or on a hot plate.

Despite its low melting point, indium has a very high boiling point of around 2072 °C, showing a wide liquid range.

Indium has a density of about 7.29 g/cm³, making it heavier than zinc and gallium but lighter than thallium.

Its crystal structure is body-centered tetragonal, a slightly distorted form of a cubic lattice arrangement.

Below 3.41 Kelvin, indium becomes a superconductor, meaning it can conduct electricity with zero resistance.

Naturally occurring indium consists mostly of the isotope indium-115, which makes up about 95.7 percent of all indium.

Indium-113 is the only stable isotope of the element, though it is much less abundant than indium-115.

Indium-115 is radioactive but has an extremely long half-life of about 4.41 × 10¹⁴ years, far longer than the age of the universe.

Indium is relatively rare in Earth’s crust, with an abundance of only about 50 parts per billion.

It is usually not found in pure form and is instead extracted as a by-product of processing zinc ores such as sphalerite.

Because it is a by-product metal, indium production depends heavily on zinc and copper mining rates rather than its own ore deposits.

Indium has no known biological role in living organisms and is generally considered toxic if inhaled or injected.

One of its most important modern uses is in indium tin oxide, a transparent conductive coating used in LCD screens.

Indium is widely used in semiconductors such as indium phosphide, indium arsenide, and indium antimonide.

These semiconductor materials are important in electronics like high-speed transistors and infrared detectors.

Indium compounds are also used in LEDs, especially in combinations like indium gallium nitride for blue and white light production.

It plays a role in thin-film solar technology through copper indium gallium selenide solar cells.

Indium is used in low-melting fusible alloys that are valuable in safety devices and thermal regulation systems.