One of the most common minerals on earth. Huge numbers of rocks with their own names are types of quartz; most beaches have sand made of grains of quartz and it acts as a natural cement between other minerals.

Pure quartz is colorless and has been used since ancient Roman times for lenses to concentrate the sun's rays; it is still used in lens systems and prisms. Its electrical properties make it useful in crystal radios, phonographs, and watches. It also has a rating of 7 on the Mohs hardness scale, making it useful in jewelry and any other purpose where a tough stone is needed.

Various added elements give quartz different colors which are used as gemstones. Some of these are: amethyst, citrine, ametrine, aventurine, and the whole chalcedony family. Several other less valuable varieties don't have their own name (but are very pretty nonetheless):

  • Smoky quartz is a tan, brown, or gray color (extremely dark smoky quartz is called morion). Radioactivity is believed to cause the color. It has been mixed up with andalusite, tourmaline and topaz in the past. It is probably the most common colored type of quartz and can be found in huge crystals which make very striking jewelry.
  • Rose quartz is pink or peach-colored and is usually rather opaque compared to most quartz gems. It is often carved into beads or even like jade into art objects. Too much weathering, though, will turn the stone grayish.
  • Quartz crystal, or rock crystal are common names to specify the clear variety. This material was often used in the past for things like rhinestones (so called because they were made from quartz pebbles found in the Rhine river valley) and fortuneteller's crystal balls.
  • Quartz is also occasionally found in all sorts of other colors such as a deep blue. It takes tests to tell if something is colored quartz or some other material.
  • Rutilated quartz is not really a separate type of quartz; any color of quartz is said to be rutilated if it contains impurities, usually golden or reddish and needle-shaped, which show through to the outside of the polish crystal. Smoky and clear quartz crystals are more likely to have this, though rose quartz has been known to show rutiles with asterism.