Quartz (KWOR-tz) is the most widespread of minerals occurring is igneous, sedimentary and metamorphic environments. the source list to the right is limited to a cross- section of those countries that currently produce significant amounts of gem quartz. crystals of colourless quartz of rock crystal are aboundant and almost inevitable the first specimens of rose quartz are so rare thet they rate among the most treasured possessions of a handful of fortune collectors. the diversity of this mineral is such that entire collection are devoted to its msny sub- varieties. small doubly terminated quartz crystals are often referred to by such misleading names as ' desert diamonds' or 'herkmer diamonds'. when colourless quartz is full of fine fractures, the thin films of air may interfere with the passage of light producing a show of rainbow colorus. this type of material is known as rainbow quartz.Pure quartz, sometimes called clear quartz, is colorless or white and transparent (clear) or translucent. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. Quartz goes by an array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite.