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Here are some USGS Web pages with more information on petrology and Anywhere:

Spectroscopy of rocks and minerals, and principles of spectroscopy Technical review of the principles of spectroscopy and its use in identifying minerals and other materials. (Score: 1.000)

North Cascades National Park geology, a mountain mosaic Homepage for information on geology of the North Cascades National Park in the state of Washington. Includes links to geologic story, geologic field trips, geologic maps, plate tectonics, rocks and minerals, geologic time, and glossary. (Score: 0.331)

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About petrology:

Definition: Study of the origin, occurrence, structure, and history of rocks, esp. igneous and metamorphic rocks. [Adapted from Glossary of Geology, 4th ed.]