Quartz is the second most abundant mineral in the Earth's continental crust, so it is no surprise that there are many and varied varieties of this crystal. When we think of Quartz, we think of clear Quartz, Rose Quartz, maybe Snow Quartz or Smoky Quartz, but gemstones such as Amethyst and Citrine are also Quartzes. It can be transparent or milky, solidly coloured or striated.
Quartz is considered to be a Master healing stone, suitable for any condition. (Crystal attributes taken from The Crystal Bible, by Judy Hall)