††Quartz is a hard, transparent crystalline mineral containing silicon (shown here on the rock). Sand is mostly made of quartz.
The first quartz-controlled clock was invented in 1928 by Joseph W. Horton and Warren Alvin Marrison. It was discovered that quartz could regulate an electronic oscillator, and therefore ensure regular time-keeping. Since then quartz has commonly been used to regulate many small electrical items, including watches, and to produce ultrasound (sounds beyond the limit of human hearing).
