Quartzite
Quartzite, a metamorphic rock derived from sandstone. In some quartzite the sand grains are recemented with silica. In others the metamorphism (change) of the sandstone results from great pressure. Quartzite is extremely hard and highly resistant to chemicals. It has a glassy luster and may be white, gray, pink, or brown. Quartzite is used in making glass and to pave roads.