quartz | Definition, Types, Uses, amp; Facts | Britannica
A brief treatment of quartz follows. For full treatment, see silica mineral. Quartz has great economic importance. Many varieties are gemstones, including amethyst, citrine, smoky quartz, and rose quartz. Sandstone, composed mainly of quartz, is an important building amounts of quartz sand (also known as silica sand) are used in the manufacture of glass and ceramics and for foundry