Quartz is a hard crystalline mineral which is found abundantly all over the Earth in a variety of forms. It is the most common mineral on Earth, making up 12% of the Earth's crust by volume, and is used in a wide variety of applications including jewelry, scientific research, manufacturing, and building. Because of its many uses, quartz is also a very important mineral, and some rare varieties are considered to be quite valuable. It can also be quite beautiful, especially when cut and polished by a jeweler who appreciates its properties. It is often used as a cheaper substitute for fancier gems, and when handled well, it can be difficult to distinguish from more expensive counterparts.
Silicon dioxide is the proper chemical name for quartz, which acquires different colors and properties depending on how it was formed. Commonly, this mineral takes on impurities that cause it to be colored, as is the case with the forms amethyst, citrine, and rose quartz. In these instances, the crystalline structure of the mineral is readily visible, and the stone can sometimes form very large clusters of distinctive crystals. These quartzes also tend to be clear, although they may have small inclusions or areas of fracture.
In other instances, the crystals are too small to see with the naked eye. This form is opaque, and sometimes called milky quartz or chalcedony. Chalcedony forms through deposits of layers of colored material, such as agate, jasper, and carnelian. Quartz can also appear mixed in with other geologic material, as is the case with granite and sandstone. Because the mineral does not dissolve readily in water, concentrations of it tend to increase as other rocks wear away, leaving mixed rocks with a high percentage of quartz in their composition.
In jewelry, quartz in many forms is abundantly used. Chalcedony can be used to make beads, cameos, and distinctive rings, while clear crystalline varieties is often cut into faceted gemstones to ornament necklaces, rings, and bracelets. More rare forms can command a high price when used in jewelry. In manufacturing, it is used as an electrical component, to manufacture specialized tools for the lab, lenses, specialized glass, and ground for use in sandpaper. Sandstone is used in building, as is granite, and most people interact with something containing quartz at least once a day, since the mineral is so prevalent in daily life.