Bibliography
- http://scienceforkids.kidipede.com/geology/rocks/igneous/quartz.htm
- http://geology.com/rocks/marble.shtml
- http://geology.com/rocks/basalt.shtml
- http://www.mindat.org/min-2999.html
- http://www.minerals.net/gemstone/onyx_gemstone.aspx
- http://www.sunnyray.org/Crystals-O.htm
- http://www.minerals.net/mineral/quartz.aspx
- http://geology.com/rocks/basalt.shtml
- http://geology.com/rocks/marble.shtml