Crystals are monocrystals of silicon dioxide (quartz), which have been used for religious and ritual purposes since ancient times, not to mention being treasured as jewelry. They still shimmer at throats and on fingers as precious stones and accessories.

In 1880, Jacques and Pierre Curie discovered their piezoelectric effect. “Piezoelectric effect” refers to the phenomenon in which, when mechanical force is applied to crystals, they produce electricity. Conversely, an electrical signal sent to a crystal causes it to vibrate mechanically in the “reverse piezoelectric effect.” When this principle (effect) is used in electrical equipment, crystals can be put to use in the electrical industry. The discovery of radio waves led to their use for communication, and crystals came to be used for stable signals. Afterward, through a diverse variety of research and results, crystals have become an indispensable electronic part for communications.
Cell phones continue to develop, digital video has become standard, automobiles are now electronic, and even household appliances are now increasingly digitized.

Crystal products are used in their radio wave oscillation sources and for time regulation among other things in both personal and industrial computers.

Elsewhere, crystals’ particular characteristics are used in industry outside the electrical field as well. When light falls on crystal material, it creates the phenomenon of birefringence, meaning there are two refractions produced; as well, there is the phenomenon of optical rotation, in which the plane of polarized light coming through crystal material rotates. Using these optical qualities, crystals are put to use in video cameras, digital cameras, optical discs and more.

In addition, they are also used in sensors such as gyroscopes. As well, crystal oscillators can be used in environmental hormone sensors and biological sensors used in medicine, a field in which research is proceeding. The future of crystals includes even broader applications as higher-precision oscillation sources, accurate time regulators, and higher-precision sensors as optical products handling light signals.