I. Rocks

B. Basic rock types

1. igneous rocks - form from cooling magma
1. intrusive or plutonic
• cool underground
• form visible mineral crystals
2. extrusive or volcanic
• cool on the surface
• small/no visible mineral crystals
2. sedimentary rocks
1. form on surface of the Earth so reveal information about environment (paleogeography)
2. often made of fragments weathered and eroded from older rocks
3. often layered (bedded)
4. sometimes contain fossils
3. metamorphic rocks
1. conditions and texture
• changed by heat and/or pressure
• sometimes foliated (flaky)
• sometimes folded
2. types
• contact and hydrothermal - high temperature
• regional - high temperature and pressure fault related - high pressure