GEOLOGY & PLANETARY SCIENCE A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site quartz A hard mineral made of crystalline silica (silicon dioxide, SiO2) that is a constituent of many rocks, especially igneous rocks such asgranite and quartzite, metamorphic rocks such as gneisses and schists, and sedimentary rocks such as sandstone and limestone. It is the second most abundant mineral on Earth after feldspar. Quartz crystallizes in the trigonal system. A well-formed quartz crystal consists of a six-sided prism that terminates in six-sided pyramids. Quartz is usually colorless and transparent, in which form it is called rock crystal. Colord varieties,a number of which are used as gemstones, include amethyst, citrine (yellow), rose quartz (pink), milk quartz (white), smokey quartz (brown), agate, jasper, carnelian, and chalcedony. It has a hardness of 7 on Mohs scale. A quartz crystal produces electricity through the process of piezoelectricity when a mechanical stress is applied to it. This has led to the use of quartz for making oscillators for clocks, radios, and radar instruments. Quartz is also used in optical instruments and in glass, glaze, and abrasives. Related category    • GEOLOGY AND PLANETARY SCIENCE Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP