From site:  Amethyst Galleries’ Mineral Gallery describes over 600 mineral species (and varieties) and more than 5000 specimens (see our new specimens last updated 09-Feb-2009, and What’s New last updated 03-Feb-2009), together with several ways of accessing these descriptions. The descriptions include searchable mineralogical data, plus other information of interest to students and rock hounds. This site displays thousands of images of previously sold mineral specimens as a service to rockhounds, students and educators (not merely minerals currently for sale).

Mineralogy 4 Kids, the Rockin Internet Site, is the BEST place to learn about rocks and minerals.  Enter mineralogy to learn about minerals in your house, mineral groups, mineral properties, all about crystals, and play some mineral games.

Get all the “dirt” on the rock cycle.  Gotta rocky question?  We’ve got the answer on the Ask-a-Mineralogist forum.

In Volcano World, kids can share volcano art, take virtual field trips, read stories and play interactive games.  For teachers, there is information on Hawaiian volcanoes, Mt. St. Helens, submarine volcanoes, volcanic gases and minerals, lessons, models, facts and a glossary.

From site:  This glossary contains simplified definitions for technical terms used within this site.

The Colorado Geology Photojournals provides excellent photos and illustrations of earth layers and the dynamic action of plate tectonics.