Quartz

is a hard white or colorless mineral consisting of silicon dioxide, found widely in igneous, metamorphic, and sedimentary rocks. It is often colored by impurities (as in amethyst, citrine, and cairngorm). Quartz is one of the most prevalent minerals involved in the formation of rocks. It is also an essential component in the crust of the earth. Quartz ranges from transparent to translucent to opaque. It may be with or without color.