GeoMan's Rock and Mineral Glossary
Includes links to other portions of the excellent website by GeoMan, Mike Strickler, Rogue Community College.
What is a Mineral?
To be classified as a mineral, a substance must be an inorganic, naturally formed solid, with a specific chemical formula and a fixed internal structure. For example, coal is not a mineral (it's organic), but snow meets all five (5) requirements and therefore is a mineral. --GeoMan
Brief but thorough identification chart.
GeoMan's Igneous Rock Notes, includes links to general information on rocks and links to charts.
U.S. Geological Survey online short course in Plate Tectonics: This Dynamic Earth.
U.S. Geological Survey short course on Geologic Time.