Quartz is an igneous gemstone.  It is the most commonly found mineral on earth.  It is common in many rocks, especially granite.  In ancient times the clear form of quartz, called rock crystal, was used to carve crystal balls and bowls.

Quartz appears in many forms.   Amethyst, citrine, onyx, and agate are all types of crystal.  Quartz is used to make beautiful jewelry.

For more pictures and information on different types of quartz go the websites listed below.

http://www.scruznet.com/~kibrick/quartz/rgdownload.html

http://mineral.galleries.com/minerals/gemstone/citrine/citrine.htm

http://www.rockhounds.com/rockshop/minimage.html