Tourmaline is a group name for boron-bearing silicate minerals, with colour varying widely by composition. Pink comes from manganese. Bicolour and watermelon specimens—where colour shifts within a single crystal—are phenomena unique to tourmaline.

It exhibits piezoelectricity: apply pressure, and it generates a charge. Pierre and Jacques Curie discovered this property in 1880. A gemstone with a place in the history of electronics.

Found in Brazil, Afghanistan, Mozambique, and California. Minas Gerais, Brazil, is particularly known for its range of colours. A stone that produces electricity when pressed.