Quartz is a common mineral found in the Earth's crust and is present in most geological formations. Most of the Earth's sand is made up of quartz.
In its natural state, quartz is used primarily as a gemstone. The United States and Brazil are major producers of quartz crystals. Quartz is almost always white or clear; exceptions include purple amethyst and yellow or orange citrine. For commercial purposes, such as use in electronics, quartz is processed to remove impurities. On the Mohs hardness scale, quartz is considered a 7 out of 10, harder than all naturally occurring minerals other than topaz, corundum and diamond.