The Rock Cycle

Three kinds of rocks will be covered in more detail in later lessons and chapters in your textbook. They are:

• Igneous rocks (literally, fire-formed)—rocks that have frozen from molten lava or magma

• Sedimentary rocks—rocks produced by weathering and erosion from older rocks at the surface of Earth

• Metamorphic rocks—rocks changed or metamorphosed from older igneous or sedimentary rocks by heat, pressure, or hot fluids produced during the collision of crustal plates, usually in the deep roots of mountain chains

Matter is not created or destroyed; it is always conserved (the law of conservation of matter)—no matter how it is chemically altered. In normal geological processes, rocks are always made from older rocks. The ways the various rocks listed above are related can be summarized by a concept known as the rock cycle. It can be diagrammed as shown in figure 1-1.