Minerals have been an essential component of human society since the discovery that, when properly struck, flint could be used to start a fire; however, the explosion in high-technology uses for minerals probably can be traced to early twentieth century experiments with crystal oscillators that were the forerunners of the modern communications industry. Since those pioneering uses of quartz, galena, and germanium crystals, technological uses for minerals have multiplied rapidly. Minerals from altaite (lead telluride) to zincite (zinc oxide) have been used to exploit their special optical or electronic properties. It is ironic that the same developments that led to so many applications for minerals also led to requirements of size, shape, and purity such that only a few minerals are suitable for use as they occur in nature. For this reason, synthetic crystal growing techniques now provide most of the highly pure, sometimes exotic, minerals used in photoconducting devices (cadmium sulfide, gallium arsenide), infrared spectrophotometers, (sodium chloride, zinc selenide), lasers (aluminum oxide), and similar instruments. The following discussion will emphasize those commercially important minerals that can be used as they occur naturally. Quartz is included because of its technical importance, and because natural quartz crystal continues to be the feedstock for synthetic crystal growth. Also featured are asbestos, calcite, and mica.