Quartz (SiO₂), a common mineral, is the product of the two most prevalent elements in the earth's crust: silicon and oxygen. Quartz can be found as giant crystals or small grains, and is the main component of most types of sand. It is the hardest common mineral, and for this reason is often used in the making of sandpaper, grindstones, polishers, and industrial cleaners. Though quartz is clear and glassy in its large crystal form, called rock quartz, it also can be found in several shades of coloration, the most familiar being rose quartz (pink), smoky quartz (brown), and amethyst (purple).

Rose quartz. U.S. National Aeronautics and Space Administration (NASA).

Quartz has a variety of scientific and industrial uses, chiefly because it possesses piezoelectricity. Discovered by the French physicist and chemist Pierre Curie (1859–1906), the piezoelectric effect is a phenomenon demonstrated by certain crystals: when squeezed or stretched...