The Rock Cycle

What is the Rock Cycle? Rock types are divided into three major groups based on how they formed: igneous, sedimentary and metamorphic. Each group contains a collection of rock types that differ from each other groups on the basis of the size, shape, and arrangement of mineral grains. The rock cycle is an illustration that is used to explain how the three rock types are related to each other and how Earth processes change a rock from one type to another through geologic time. Plate tectonic movement is responsible for the recycling of rock materials and is the driving force of the rock cycle.

Igneous Rock There are places on Earth that are so hot that rocks melt to form magma. Because magma is liquid and usually less dense than surrounding solid rock, it moves upward to cooler regions of the Earth. As the magma loses heat, it cools and crystallizes into an igneous rock. Magma can cool on the Earth's surface, where it has erupted from a volcano (extrusive rock) or under the Earth's surface, where it has intruded older rocks (intrusive rock).

Basalt Andesite Rhyolite Diorite Granite Gabbro

Metamorphic Rock Any rock (igneous, sedimentary or metamorphic) can become a metamorphic rock. If rocks are buried deep in the Earth at high temperatures and pressures, they form new minerals and textures all without melting. If melting occurs, magma is formed, starting the rock cycle all over again.

Slate Gneiss Quartzite Marble

Sedimentary Rock Any rock (igneous, sedimentary, or metamorphic) exposed at the Earth's surface can become a sedimentary rock. The forces of wind, rain, snow, and ice combine to break down or dissolve (weather), and carry away (transport) rocks exposed at the surface. These particles eventually come to rest (deposited) and become hard rock (lithified). Sedimentary rocks tell us what the Earth's surface was like in the geologic past. They can contain fossils that tell us about the animals and plants or show the climate in an area. Sedimentary rocks are also important because they may contain water for drinking or oil and gas to run our cars and heat our homes.

Breccia Sandstone Conglomerate Gypsum Limestone

What type of rock do I have? Igneous rocks are recognized by: * the interlocking texture of the grains * the presence of vesicules (holes) in extrusive igneous rocks * may be dark-colored and heavy * may display two grain sizes, one much larger than the other Sedimentary rocks are recognized by: * grains cemented together * the presence of fossils * light-colored and light weight * may display interlocking grains but is very light weight Metamorphic rocks are recognized by: * the interlocking texture of large grains * foliation (layering) * banded light and dark colors * "ching" sound instead of a "chunk" sound when tapped

Puu Oo, Kilauea (1983-1986).