Other
Mineralogical Society of America: Mineral Groups
Investigate the seven different groups of minerals. In-depth information is provided on the chemistry of members of each mineral group. Pictures of different minerals are also provided.
University of Oregon
Geo Man's Mineral and Rock Charts
This site contains several charts that can be used for identifying rocks and minerals based on traits such as hardness, luster and color.
Amethyst Galleries
Amethyst Galleries: Mineral Gallery: Minerals by Class
This is a detailed reference list of minerals and mineral classes.