What are metamorphic rocks?
Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic euro-caspian.comrphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, . Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Examples of foliated rocks include: gneiss, phyllite, schist, and slate. Non-foliated metamorphic rocks do not have a layered or banded appearance.
A metamorphic rock used to be some other type of rock, but it was changed inside the Earth to become a new type of rock. The type of rock that a metamorphic rock used to be, prior to metamorphism, is called the protolith. During metamorphism the mineral content and texture of the protolith are changed due to changes in the physical and chemical environment of the rock. Metamorphism can be caused by burial, tectonic stress, heating by magma, or alteration by fluids.
At advanced stages of metamorphism, it is common for a metamorphic rock to develop such a different set of minerals and such a thoroughly changed texture that it is difficult to recognize what the protolith was. A rock undergoing metamorphism remains a solid rock during the process. Rocks do not melt during most conditions of metamorphism.
At the highest grade of metamorphism, rocks begin to partially melt, at which point the boundary of metamorphic conditions is surpassed and the igneous part of the rock cycle is entered. Even though rocks remain solid during metamorphism, fluid is generally present in the microscopic spaces between the minerals.
This fluid phase may play a major role in the chemical reactions that are an important part of how metamorphism occurs. The fluid usually consists largely of water. Metamorphic rocks provide a record of the processes that occurred inside Earth as the rock was subjected to changing physical and chemical conditions. Metamorphic rocks are like probes that have gone down into the Earth and come back, bringing an record of the conditions they encountered on their journey in the depths of the Earth.
Figure 1. The platy layers in this large outcrop of metamorphic rock show the effects of pressure on rocks during metamorphism. Metamorphic rocks may change so much that they may not resemble the original rock. Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals.
Ions may move between minerals to create minerals of different chemical composition. Hornfels, with its alternating bands of dark and light crystals, is a good example of how minerals rearrange themselves during metamorphism.
Hornfels is shown in table 1. Extreme pressure may also lead to foliationthe flat layers that form in rocks as the rocks are squeezed by pressure what do metamorphic rocks form 2. Foliation normally forms when pressure is exerted in only one direction. Metamorphic rocks may also be non-foliated. Quartzite and limestone, shown in table 6, are nonfoliated. What do metamorphic rocks form reason rocks undergo metamorphism is that the minerals in a rock are only stable under a limited range of pressure, temperature, and chemical conditions.
When rocks are subjected to large enough changes in these factors, the minerals will undergo chemical reactions that result in their replacement by new minerals, minerals that are stable in the new conditions. The type of rock undergoes metamorphism is a major factor in determing what type of metamorphic rock it becomes. In short the identify of the protolith plays a big role the identity of the metamorphic rock. A fluid phase may introduce or remove chemical substances into or out of the rock during metamorphism, but in most metamorphic rock, most of the atoms in the protolith are be present in the metamorphic rock after metamorphism; the atoms will likely be rearranged into new mineral forms within the rock.
Therefore, not only does the protolith determine the initial chemistry of the metamorphic rock, most metamorphic rocks do not change their bulk overall chemical compositions very much during metamorphism.
The fact that most what do metamorphic rocks form rocks retain most of their original atoms means that even if the rock was so thoroughly metamorphosed that it no longer looks at all like the protolith, the rock can be analyzed in terms of its bulk chemical composition to determine what type of rock the protolith was.
Temperature is another major factor of metamorphism. There are two ways to think about how the temperature of a rock can be increased as a result of geologic processes. If rocks are buried within the Earth, the deeper they go, the higher the temperatures they experience. This is because temperature inside the Earth increases along what is called the geothermal gradient, or geotherm for short.
Therefore, if rocks are simply buried deep enough enough sediment, they will experience temperatures high enough to cause metamorphism. Tectonic processes are another way rocks can be moved deeper along the geotherm.
Faulting and folding the rocks of the crust, can move rocks to much greater depth than simple burial can. Magma intrusion subjects nearby rock to higher temperature with no increase in depth or pressure. Pressure is a measure of the stress, the physical force, being applied to the surface of a material. It is defined as the force per unit area acting on the surface, in a direction perpendicular to the surface. Lithostatic pressure is the pressure exerted on a rock by all the surrounding rock.
The source of the pressure is the weight of all the rocks above. Lithostatic pressure increases as depth within the Earth increases and is a uniform stress— the pressure applies equally in all directions on the rock.
If pressure does not apply equally in all directions, differential stress occurs. There are two types of differential stress. Normal stress compresses pushes together rock in one direction, the direction of maximum stress. At the same time, in a perpendicular direction, the rock undergoes tension stretchingin the direction of minimum stress. Shear stress pushes one side of the rock in a direction parallel to the side, while at the same time, the other side of the rock is being pushed in the opposite direction.
Differential stress has a major influence on the the appearance of a metamorphic rock. Differential stress can flatten pre-existing grains in the rock, as shown in the diagram below.
Metamorphic minerals that grow under differential stress will have a preferred orientation if the minerals have atomic structures that tend to make them form either flat or elongate crystals. This will be especially apparent for micas or other sheet silicates that grow during metamorphism, such as biotite, muscovite, chlorite, talc, or serpentine.
If any of these flat minerals are growing under normal stress, they will grow with their sheets oriented perpendicular to the direction of maximum compression. This results in a rock that can what are the parts of a typical windows screen easily broken along the parallel mineral sheets.
Such a rock is said to be foliated, or to have foliation. Any open space between the mineral grains in a rock, however microscopic, may contain a fluid phase.
Most commonly, if there is a fluid phase in a rock during metamorphism, it will be a hydrous fluid, consisting of water and things dissolved in the water. Less commonly, it may be a carbon dioxide fluid or some other fluid. The presence of a fluid how to move buildings in hay day is a major factor during metamorphism because it helps determine which metamorphic reactions will occur and how fast they will occur.
The fluid phase can also influence the rate at which mineral crystals deform or change shape. Most of this influence is due to the dissolved ions that pass in and out of the fluid phase. If during metamorphism enough ions are introduced to or removed from the rock via the fluid to change the bulk chemical composition of the rock, the rock is said to have undergone metasomatism. However, most metamorphic rocks do not undergo sufficient change in their bulk chemistry to be considered metasomatic rocks.
Most metamorphism of rocks takes place slowly inside the Earth. Regional metamorphism takes place on a timescale of millions of years. Metamorphism usually involves slow changes to rocks in the solid state, as atoms or ions diffuse out of unstable minerals that are breaking down in the given pressure and temperature conditions and migrate into new minerals that are stable in those conditions.
This type of chemical reaction takes a long time. Metamorphic grade refers to the general temperature and pressure conditions that prevailed during metamorphism.
As the pressure and temperature increase, rocks undergo metamorphism at higher metamorphic grade. Rocks changing from one type of metamorphic rock to another as they encounter higher grades of metamorphism are said to be undergoing prograde metamorphism.
This is not far beyond the conditions in which sediments get lithified into sedimentary rocks, and it is common for a low-grade metamorphic rock to look somewhat like its protolith.
Low grade metamorphic rocks tend to characterized by an abundance of hydrous minerals, minerals that contain water within their crystal structure. Examples of low grade hydrous minerals include clay, serpentine, and chlorite.
Under low grade metamorphism many of the metamorphic minerals will not grow large enough to be seen without a microscope. Low grade hydrous minerals are replaced by micas such as biotite and muscovite, and non-hydrous minerals such as garnet may grow. Garnet is an example of a mineral which may form porphyroblasts, metamorphic mineral grains that are larger in size and more equant in shape about the same diameter in all directionsthus standing out among the smaller, flatter, or more elongate minerals.
Micas tend to break down. New minerals such as hornblende will form, which is stable at higher temperatures. However, as metamorphic grade increases to even higher grade, all hydrous minerals, which includes hornblende, may break down and be replaced by other, higher-temperature, non-hydrous minerals such as pyroxene. Index how long to get pregnant after vasectomy reversal, which are indicators of metamorphic grade.
In a given rock type, which starts with a particular chemical composition, lower-grade index minerals are replaced by higher-grade index minerals in a sequence of chemical reactions that proceeds as the rock undergoes prograde metamorphism. For example, in rocks made of metamorphosed shale, metamorphism may prograde through the following index minerals:.
Index minerals are used by geologists to map metamorphic grade in regions of metamorphic rock. A geologist maps and collects rock samples across the region and marks the geologic map with the location of each rock sample and the type of index mineral it contains.
By drawing lines around the areas where each type of index mineral occurs, the geologist delineates the zones of different metamorphic grades in the region. The lines are known as isograds. Regional metamorphism occurs where large areas of rock are subjected to large amounts of differential stress for long intervals of time, conditions typically associated with mountain building. Mountain building occurs at subduction zones and at continental collision zones where two plates each bearing continental crust, converge upon each other.
Most foliated metamorphic rocks—slate, phyllite, schist, and gneiss—are formed during regional metamorphism. As the rocks become heated at depth in the Earth during regional metamorphism they become ductile, which means they are relatively soft even though they are still solid.
The folding and deformation of the rock while it what do metamorphic rocks form ductile may greatly distort the original shapes and orientations of the rock, producing folded layers and what is the best volumizing shampoo and conditioner veins that have highly deformed or even convoluted shapes.
The diagram below shows folds forming during an early stage of regional metamorphism, along with development of foliation, in response to normal stress. The photograph below shows high-grade metamorphic rock that has undergone several stages of foliation development and folding during regional metamorphism, and may even have reached such a high temperature that it began to melt. Contact metamorphism occurs to solid rock next to an igneous intrusion and is caused by the heat from the nearby body of magma.
Because contact metamorphism is not caused by changes in pressure or by differential stress, contact metamorphic rocks do not become foliated. Where intrusions of magma occur at what is the meaning of will power levels of the crust, the zone of contact metamorphism around the intrusion is relatively narrow, sometimes only a few m a few feet thick, ranging up to contact metamorphic zones over m over feet across around larger intrusions that released more heat into the as a graphic designer what should i know crust.
Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form. As the temperature and/or pressure increases on a body of rock we say that the rock undergoes prograde metamorphism or that the grade of metamorphism increases. Rocks that form at high temperatures generally do not have the same problems. However, there are many kinds of metamorphic rocks, and some of them are more chemically reactive than others. Sheared serpentinite with pencil for scale, Marin County, California. Low-grade metamorphic rocks form at low temperatures, generally between and A metamorphic rock used to be some other type of rock, but it was changed inside the Earth to become a new type of rock. The word metamorphism comes from ancient Greek words for “change” (meta) and “form.
Igneous, Sedimentary vs Metamorphic Rocks. The main difference between Igneous, Sedimentary and Metamorphic rocks, is the way that they are formed, and their various textures. Igneous rocks are formed when magma or molten rocks cool down, and become solid. High temperatures inside the crust of the Earth cause rocks to melt, and this substance is known as magma.
Magma is the molten material that erupts during a volcano. This substance cools down slowly, and causes mineralization to take place.
Gradually, the size of the minerals increase until they are large enough to be visible to the naked eye. The texture of Igneous rocks can be referred to as Phaneritic, Aphaneritic, Glassy or vitreous , Pyroclastic or Pegmatitic.
Examples of Igneous Rocks include granite, basalt and diorite. Therefore, one can say, that these types of rocks are formed slowly from the sediments, dust and dirt of other rocks. Erosion takes place due to wind and water. After thousands of years, the eroded pieces of sand and rock settle, and become compacted to form a rock of their own. Sedimentary rocks range from small clay-size rocks to huge boulder-size rocks. The textures of Sedimentary rocks are mainly dependent on the parameters of the clast, or the fragments of the original rock.
These parameters can be of various types, such as surface texture, round, spherical or in the form of grain. The most common type of Sedimentary rock is the Conglomerate, which is caused by the accumulation of small pebbles and cobbles. Other types include shale, sandstone and limestone, which is formed from clastic rocks and the deposition of fossils and minerals. Metamorphic rocks are the result of the transformation of other rocks. Rocks that are subjected to intense heat and pressure change their original shape and form, and become Metamorphic rocks.
This change in shape is referred to as metamorphism. These rocks are commonly formed by the partial melting of minerals, and re-crystallization. Gneiss is a commonly found Metamorphic rock, and it is formed by high pressure, and the partial melting of the minerals contained in the original rock.
Metamorphic rocks have textures like slaty, schistose, gneissose, granoblastic or hornfelsic. Examples of these types of rocks include slate, gneiss, marble, and quartzite, which occurs when re-crystallization changes the shape and form of an original rock formation. Summary: 1. Igneous rocks are formed when magma or molten rocks have cooled down and solidified. Sedimentary rocks are formed by the accumulation of other eroded substances, while Metamorphic rocks are formed when rocks change their original shape and form due to intense heat or pressure.
Igneous rocks can be an important source of minerals, and Sedimentary rocks, or their bedding structure, is mostly used in civil engineering; for the construction of housing, roads, tunnels, canals etc. Examples of Igneous rocks include granite and basalt, while examples of Sedimentary rocks include shale, limestone and sandstone. Common examples of Metamorphic rocks are marble, slate and quartzite. Cite Colleen.
February 17, Rock that has formed through the deposition and solidification of sediment, especially sediment transported by water rivers, lakes, and oceans , ice glaciers , and wind. Sedimentary rocks are often deposited in layers, and frequently contain fossils. I love the app it works very well with my homework do you love it cuz I love it whoever made this good job we are learning about rocks.
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