Once exposed, they are weathered, both physically by mechanical breaking of the rock and chemically by weathering of the minerals , and the weathering products — mostly small rock and mineral fragments — are eroded, transported, and then deposited as sediments.
Transportation and deposition occur through the action of glaciers, streams, waves, wind, and other agents, and sediments are deposited in rivers, lakes, deserts, and the ocean. Referring to the rock cycle Figure 3. A conservative estimate is that each of these steps would take approximately 20 million years some may be less, others would be more, and some could be much more. How long might it take for this entire process to be completed?
Unless they are re-eroded and moved along, sediments will eventually be buried by more sediments. Usually, the rock pieces, called sediments, drop from the wind or water to make a layer.
The layer can be buried under other layers of sediments. After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock can become sedimentary rock.
All rock can be heated. But where does the heat come from? Inside Earth there is heat from pressure push your hands together very hard and feel the heat. There is heat from friction rub your hands together and feel the heat. There is also heat from radioactive decay the process that gives us nuclear power plants that make electricity.
So, what does the heat do to the rock? It bakes the rock. Remember, all rocks are made up of mineral crystals, or pieces of other rocks made up of crystals. Baked rock does not melt, but it does change. It forms crystals. If it has crystals already, it forms larger crystals. Because this rock changes, it is called metamorphic. Remember that a caterpillar changes to become a butterfly. That change is called metamorphosis. Metamorphosis can occur in rock when they are heated to to degrees Celsius.
When Earth's tectonic plates move around, they produce heat. When they collide, they build mountains and metamorphose the rock. The rock cycle continues. Mountains made of metamorphic rocks can be broken up and washed away by streams. New sediments from these mountains can make new sedimentary rock. The rock cycle never stops.
Igneous Rocks : Igneous rocks are a type of rock formed from extremely hot 2, degrees F molten masses known as magma. Generally, magma lies about 90 miles below the surface. In certain places, such as Yellowstone National Park, the magma is as close as 40 miles below the surface. On average, every feet you dig down into the earth, the temperature will increase about 1. Sometimes magma forces its way up to the surface through a vent such as a volcano and spills onto the surface.
This happened near Flagstaff, Arizona at Sunset Crater less than 1, years ago. Once magma comes out onto the surface of the earth it is called lava, and it cools rapidly at the surface. Extrusive igneous rocks can be distinguished by their small crystal sizes. In all extrusive igneous rock, it is nearly impossible to detect crystals without the aid of a microscope.
The faster the rock cools, the smaller the crystals. Some extrusive igneous rocks cool so quickly that they have a glassy texture. Common extrusive igneous rocks are: andesite, basalt, dacite, pumice, rhyolite, and obsidian. Intrusive igneous rocks solidify over a period of thousands of years. This slow cooling rate allows better development of mineral crystals. Intrusive igneous rocks will have eye visible crystals and will appear coarse-grained.
Igneous intrusive rocks eventually will become exposed at the surface of the earth by erosion of the overlying material.
Common intrusive igneous rocks are: granite, diorite, gabbro, and peridotite. The La Sal Mountains were formed by widespread igneous activity that began about 40 million years ago. Caldera explosions erupted thousands of cubic miles of volcanic rocks from several locations. Volcanoes spewed ash and lava. For 20 million years these extrusive volcanic rocks smoothed the landscape, filling depressions with accumulations of ash, flows, and debris literally miles thick.
These mostly pastel-colored extrusive rocks still blanket much of the high areas of central and southwestern Utah. Not all of the molten rising igneous material erupted as volcanic rocks; some material, along with its mineral-bearing fluids, congealed in the earth's crust.
Several of these intruded masses having been exposed by erosion or encountered out by exploration drilling became great mining districts, such as at Alta, Brighton, Bingham, Park City, and Cedar City. In the Colorado Plateau, bodies of intrusive rocks domed the overlying sedimentary rocks to form the Abajo and Henry Mountains as well as the La Sal Mountains.
NOTE: This paragraph on laccoliths borrowed from here. Rocks which have undergone these sorts of changes are called metamorphic rocks. Agents of Matamorphosis. The three primary agents which metamorphose rock are temperature, pressure, and fluids.
High temperatures can change rock by changing the structure of the minerals which make up the rocks; changing the structure of the minerals changes them into new minerals remember the definition of a mineral. This increase in temperature with increase in depth is called the geotherm. Intrusions Another source of high temperatures inside the Earth is magma intruding cooler rock.
These temperature increases are localized near the intrusion, but also metamorphose rock this is called contact metamorphism. Pressure or more properly, stress can also change rock.
There are two main kinds I want you to know about: Confining Pressure Pressure due to the weight of overlying rock. This kind of pressure is roughly the same in all directions this is like water pressure when scuba diving , and is the kind which compacts rock during diagenesis. Confining pressure changes rock by compaction and by changing the crystal structure of minerals from relatively open forms to more densely-packed forms. One mineral which does this is olivine, which changes from olivine isolated silica tetrahedra to spinel a much more tightly-bonded structure to perovskite a still more highly compressed structure.
This kind of pressure is usually due to tectonic forces. It changes rocks by changing the structure of minerals and by changing the orientation of mineral grains, particularly platy minerals like mica or clay. Fluids which metamorphose rock are not pore fluids remaining from when sedimentary rocks were deposited.
Instead, they come from two main sources: hydrothermal fluids from magmatic intrusions and dehydration of minerals, like clay, which contain water in their structures hydrous minerals. Whatever the source, fluids contain ions dissolved from other rock or from their original source. An example of this would be pumice. Any rock type can become any other.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Metamorphic rocks start as one type of rock and—with pressure, heat, and time—gradually change into a new type of rock.
Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Igneous rocks are one of three main types of rocks along with sedimentary and metamorphic , and they include both intrusive and extrusive rocks. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Photograph by Steve Raymer.
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