Information on mineralogy is often hard to find on the web, so the University of Wurzburg Institute of Mineralogy in Germany has created a comprehensive set of links that cover a wealth of topics.  They include teaching materials at different levels, information on experimental and analytical techniques, thermobarometry, mineral descriptions and crystallography, economic mineralogy, gemmology and much more besides.  Go to http://www.uni-wuerzburg.de/mineralogie/links.html