Barium carbonate

Barium carbonate is a heavy white powder made of one barium atom, one carbon atom and three oxygen atoms. It doesn't dissolve in water, but stomach acid dissolves it, and the barium is poisonous. It has been used as rat poison.

It occurs naturally as the fairly rare mineral witherite, but most is made from barite, which is barium sulfate. Barite is crushed and heated with coke in a kiln at around 1,000 °C. The carbon pulls oxygen off the sulfate, leaving barium sulfide, which dissolves in water. The solution is then treated with carbon dioxide gas or with sodium carbonate. Barium carbonate comes out of solution as a fine white powder, which is filtered, washed and dried. For electronics, it's purified further and its grain size carefully controlled.

Mixed with titanium dioxide and heated, it releases carbon dioxide and becomes barium titanate, the ceramic inside ceramic capacitors. It's also used in special glasses and ceramic glazes, and in brickmaking, where it stops white salt stains from forming on walls.