Phantoms are a result of inclusions which occur when other minerals such as chlorite , hematite or even milky quartz form as a crust on the surface of the crystals during an hiatus in the crystal's growth. The crystal then grows out and around the encrusting growth encasing it inside. But since the thin encrustations formed over a crystal complete with crystal faces it appears that there is a crystal inside the crystal. The encrustations are often incomplete or diffuse and appear ghostly, hence the name phantom . Rock crystal is only one of several 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. Milky Quartz is the cloudy white variety. Rose quartz is a pink to reddish pink variety. Smoky quartz is the brown to gray variety.