Tin dioxide

Tin dioxide, SnO₂, is a white, very stable powder. It's the same compound as cassiterite, the dark mineral that is the world's main ore of tin. So making it for electronics turns tin back into the form it was mined in, only far purer.

To make it, refined tin metal is heated in air or oxygen so it burns to the oxide, or it's dissolved, precipitated from solution and then heated. For electronics the powder is milled very fine so it mixes evenly with indium oxide.

In indium tin oxide it makes up about 10% by weight, and that small share is what makes the film a good conductor. Each tin atom that takes the place of an indium atom in the crystal brings one more electron than the spot needs, and that spare electron is free to move and carry current.

Tin dioxide has other jobs too. Doped with fluorine, it's a cheaper clear conductor used on energy-saving window glass and some solar panels. It's also the sensing material in many gas detectors, and a polishing powder for glass and stone.