Wikipedia: Rock (Geology)
Hyperlinked article overview of the study of rocks. Includes definitions of the three main rock types: igneous, sedimentary, and metamorphic.
Petrogenesis of Rocks and Minerals, The
Examines the means by which a rock or mineral deposit is formed. Outlines igneous, metamorphic, and sedimentary process as well as vein environments.
Teaching Petrology in the 21st Century
Clearinghouse for a variety of educational and supporting materials for teaching igneous and metamorphic petrology.
Visions of Earth
National Geographic feature about the work of Bill Atkinson, capturing the beauty of intense close-ups of rock cross-sections.