Quartz is the second most common mineral in Earth's crust. Many varieties are precious gemstones, including amethyst, citrine, smoky quartz, brandy quartz, and rose quartz. 

Quartz makes an excellent gemstone. It is hard, durable, and usually accepts a brilliant polish.

Quartz grows primarily in pegmatites but is hydrothermally grown in laboratories. Quartz grows very large, with cut gems in the thousands of carats. The exceptions are amethyst, which rarely produces a clean gem of 100 carats, and rose quartz, which rarely exceeds 30 carats in a transparent gem.