Milky quartz is only one of several different quartz varieties. Amethyst is the purple gemstone variety. Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. Rock crystal is the clear variety that is also used as a gemstone. Rose quartz is a pink to reddish pink variety.
Smoky quartz is the brown to gray variety.
Agate is a general term for several microscopic quartz varieties.