Interactives . The Rock Cycle . Types of Rocks Types of Rocks Rocks are not all the same! The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. Sedimentary Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone. Metamorphic Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. Examples of this rock type include gneiss and marble.

Igneous Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock. Examples of this rock type include basalt and obsidian. Here's a chart of some of the key characteristics that can help you identify the rocks within these three main classes. Crystals Small, flat surfaces that are shiny or sparkly, like tiny mirrors. Fossils Imprints of leaves, shells, insects, or other items in the rock. Gas bubbles "Holes," like Swiss cheese, in the rock. Glassy surface A shiny and smooth surface, like colored glass. Ribbonlike layers Straight or wavy stripes of different colors in the rock.

Sand or pebbles Metamorphic Rock: Face of the Earth Home | Games | Glossary | Bulletin Board | Landforms | Rock Cycle | Processes | SKC Homepage Metamorphic Rock Metamorphic rock is rock that has been altered by heat or by heat and pressure. �Metamorphic' means �change of form'; heat and pressure can change the forms of many things, for example, a glassmaker uses heat to change a certain kind of sand into glass. Rocks change when mountain-building forces apply a great deal of pressure and heat to them. Rock is changed by heat produced by nearby molten igneous rock, that is, molten rock, or by both heat and pressure produced mainly by movements in the earth's surface which are associated with the formation of mountains. These rocks formed from other rocks by essentially solid state changes in mineralogy and textures resulting from chemical or physical changes that occur in solid rock buried in the earth's crust are called metamorphic rocks. They have been changed usually by heat and pressure from their original condition into rock with new minerals and structures; some of the minerals in rock are broken down and form new minerals. The grains that make up the rock may become larger.

The mineral content of metamorphic rocks depends both on its protolith and the metamorphic conditions the rocks endured. The presence of some specific minerals in a metamorphic rock can indicate the degree of heat and pressure it sustained. Metamorphic rocks are sedimentary or igneous rocks that have been modified or changed in form, that is, the size, shape and arrangement of the minerals in rocks, by heat or pressure. As they are derived from previously existing igneous, sedimentary or even metamorphic rock, their appearance varies from one to the other. Metamorphic rocks are identified by the types of minerals they contain and their texture. Examples of sedimentary rocks changing to metamorphic rock as a result of heat and pressure are limestone changing to marble, and shale changing to slate. Metamorphic Rocks Lesson #14 Metamorphic Rocks Lesson #14 Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks form when rocks are heated to the melting point which forms magma .

Sedimentary rocks are formed from the cementing together of sediments, or from the compaction (squeezing together) of sediments, or from the recrystallization of new mineral grains which are larger than the original crystals. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock. The word "metamorphic" comes from Greek and means "To Change Form". The diagram above shows you how the rocks on Earth have been changed continually over time from one rock type to another. This changing of rock types is called the "Rock Cycle". Solid rock can be changed into a new rock by stresses that cause an increase in heat and pressure. There are 3 main agents that cause metamorphism. Factors that cause an increase in Temperature, Pressure, and Chemical changes are the three agents that we are going to study. Temperature increases can be caused by layers of sediments being buried deeper and deeper under the surface of the Earth. As we descend into the earth the temperature increases about 25 degrees Celsius for every kilometer that we descend. The deeper the layers are buried the hotter the temperatures become.

The great weight of these layers also causes an increase in pressure, which in turn, causes an increase in temperature. shearing effect of the plates sliding past each other causes the rocks coming in contact with the descending rocks to change. Some of the descending rock will melt because of this friction. When rock melts it is then considered igneous not metamorphic, but the rock next to the melted rock can be changed by the heat and become a metamorphic rock. The diagram above shows you where metamorphic rock (YELLOW ZONE) can be produced at a subduction zone. There are 3 factors that cause an increase in pressure which also causes the of metamorphic rocks. These factors are; 1. The huge weight of overlying layers of sediments. 2. Stresses caused by plates colliding in the process of mountain building. 3. Stresses caused by plates sliding past each other, such as the shearing stresses at the San Andreas fault zone in California. Factors that cause chemical changes in rocks also contribute to the formation of metamorphic rocks. Very hot fluids and vapors can, because of extreme pressures, fill the pores of existing rocks.

These fluids and vapors can cause chemical reactions to take place, that over time, can change the chemical makeup of the parent rock. Metamorphism can be instantaneous as in the shearing of rocks at plate boundaries or can take millions of years as in the slow cooling of magma buried deep under the surface of the Earth. There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism. Contact Metamorphism occurs when magma comes in contact with an already existing body of rock. When this happens the existing rocks temperature rises and also becomes infiltrated with fluid from the magma. The area affected by the contact of magma is usually small, from 1 to 10 kilometers. Contact metamorphism produces non-foliated (rocks without any ) rocks such as marble, quartzite, and hornfels. In the diagram above magma has pushed its way into layers of limestone, quartz sandstone and shale. The heat generated by the magma chamber has changed these sedimentary rocks into the metamorphic rocks marble, quartzite, an hornfels. Regional Metamorphism occurs over a much larger area. This metamorphism produces rocks such as gneiss and schist.

Regional metamorphism is caused by large geologic processes such as mountain-building. These rocks when exposed to the surface show the unbelievable pressure that cause the rocks to be bent and broken by the mountain building process. Regional metamorphism usually produces foliated rocks such as gneiss and schist. Dynamic Metamorphism also occurs because of mountain-building. These huge forces of heat and pressure cause the rocks to be bent, folded, crushed, flattened, and sheared. Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away. Many metamorphic rocks are found in mountainous regions today and are a good indicator that ancient mountains were present in areas that are now low hill or even flat plains. Metamorphic rocks are divided into two categories- Foliates and Non-foliates. Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock.

Slate, as an example, will split into thin sheets. Foliate comes from the Latin word that means sheets, as in the sheets of paper in a book. Silt and clay can become deposited and compressed into the sedimentary rock shale. The layers of shale can become buried deeper and deeper by the process of deposition. Deposition is the laying down of rock forming material by any natural agent (wind, water, glaciers) over time. Because these layers are buried, temperatures and pressures become greater and greater until the shale is changed into slate. Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown . Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures. Slate has been used by man in a variety of ways over the years. One use for slate was in the making of headstones or grave markers. Slate is not very hard and can be carved easily. The problem with slate though is its perfect cleavage. The slate headstones would crack and split along these cleavage planes as water would seep into the cracks and freeze which would lead to expansion.

This freeze-thaw, freeze-thaw over time would split the headstone. Today headstones are made of a variety of rocks, with granite and marble being two of the most widely used rocks. Slate was also used for chalk boards. The black color was good as a background and the rock cleaned easily with water. Today it is not very advantageous to use this rock because of its weight and the splitting and cracking over time. Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye. Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main minerals that they are formed from. Bitotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this. Gneiss is a high grade metamorphic rock.

This means that gneiss has been subjected to more heat and pressure than schist. Gneiss is coarser than schist and has distinct banding. This banding has alternating layers that are composed of different minerals. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite. Gneiss can be used by man as paving and building stone. Non-Foliates are metamorphic rocks that have no cleavage at all. Quartzite and marble are two examples of non-foliates that we are going to study. Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock. The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains.

Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate (CaCO3). Marble has many different sizes of crystals. Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green. Marble is much harder than its parent rock. This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists. Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges. Marble is quarried in Vermont, Tennessee, Missouri, Georgia, and Alabama. Write the answers to the following questions in complete sentences on a piece of paper. 1. Write a definition in your own words of what a metamorphic rock is. 2. What are the three agents of metamorphism? 3. What are the three types of metamorphism? 4. Minerals/ Rock types Minerals/ Rock types Igneous Rocks Igneous rock is formed when magma cools and makes crystals.

Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly or igneous rock can form above ground, where the magma cools quickly. Igneous rock is formed when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly or igneous rock can form above ground, where the magma cools quickly.

Igneous Rocks Sedimentay Rocks Sedimentary rocks form at or near the earth's surface at relatively low temperatures and pressures primarily by: deposition by water, wind or ice precipitation from solution (may be biologically mediated) growth in position by organic processes (e.g., carbonate reefs ) Sediment can either be: Material, originally suspended in a liquid, that settles at the bottom of the liquid when it is left standing for a long time Material eroded from preexisting rocks that is transported by water, wind, or ice and deposited elsewhere Sedimentary rocks form at or near the earth's surface at relatively low temperatures and pressures primarily by: deposition by water, wind or ice precipitation from solution (may be biologically mediated) growth in position by organic processes (e.g., carbonate reefs ) Sediment can either be: Material, originally suspended in a liquid, that settles at the bottom of the liquid when it is left standing for a long time Material eroded from preexisting rocks that is transported by water, wind, or ice and deposited elsewhere Sedimentay Rocks Metamorphic Rock Metamorphic Rock is formed when rocky material experiences intense heat and pressure in the crust of the earth.

Through the metamorphic process, both igneous rocks and sedimentary rocks can change into metamorphic rocks, and a metamorphic rock can change into another type of metamorphic rock. Heat and pressure do not change the chemical makeup of the parent rocks but they do change the mineral structure and physical properties of those rocks. Metamorphic rocks trapped underground are still subject to enormous heat from rising magma, or heated water, and pressure. Sometimes the heat can get so intense the rocks actually melt. Pressure comes from the incredible weight of material surrounding the rock on all sides. The pressure pushes new minerals into the rock and drives other minerals out; the result, of course, is that the rock is chemically changed. Metamorphic Rock is formed when rocky material experiences intense heat and pressure in the crust of the earth. Through the metamorphic process, both igneous rocks and sedimentary rocks can change into metamorphic rocks, and a metamorphic rock can change into another type of metamorphic rock. Heat and pressure do not change the chemical makeup of the parent rocks but they do change the mineral structure and physical properties of those rocks. Metamorphic rocks trapped underground are still subject to enormous heat from rising magma, or heated water, and pressure.

Sometimes the heat can get so intense the rocks actually melt. Pressure comes from the incredible weight of material surrounding the rock on all sides. The pressure pushes new minerals into the rock and drives other minerals out; the result, of course, is that the rock is chemically changed. Metamorphic Rock Weathering The process in which rocks are broken down by chemical and/or physical mechanisms into smaller particles. There are three types of weathering Physical weathering: physical action which breaks up rocks. An example of this is freethaw weathering Chemical Weathering: when the rock is attacked by chemicals. An example of this is how acid rain breaks down limestone. Biological weathering: occurs when rocks are weakened and broken down by animals and plants. A tree root system that is slowly splitting rocks is an example of this type of weathering.. Erosion is the wearing away of exposed surfaces by agents such as wind, moving water and ice. These agents usually contain weathered rock debris. Rock fall under gravity is also erosion. Erosion influences orogenesis by changing the topography and hence the thickness of the deforming orogen, which, in turn results in modification of the gravitational force relative to the tectonic driving force.

Whereas efficient erosion tends to localize deformation within a relatively narrow belt, decrease in erosional efficiency causes deformation to propagate toward more distal sites. Transportation: This process occurs when the particles created by weathering are carried by ice, air, or water to a region of lower energy known as a sedimentary basin. The process in which rocks are broken down by chemical and/or physical mechanisms into smaller particles. There are three types of weathering Physical weathering: physical action which breaks up rocks. An example of this is freethaw weathering Chemical Weathering: when the rock is attacked by chemicals. An example of this is how acid rain breaks down limestone. Biological weathering: occurs when rocks are weakened and broken down by animals and plants. A tree root system that is slowly splitting rocks is an example of this type of weathering.. Erosion is the wearing away of exposed surfaces by agents such as wind, moving water and ice. These agents usually contain weathered rock debris. Rock fall under gravity is also erosion. Erosion influences orogenesis by changing the topography and hence the thickness of the deforming orogen, which, in turn results in modification of the gravitational force relative to the tectonic driving force.

Whereas efficient erosion tends to localize deformation within a relatively narrow belt, decrease in erosional efficiency causes deformation to propagate toward more distal sites. Transportation: This process occurs when the particles created by weathering are carried by ice, air, or water to a region of lower energy known as a sedimentary basin. Weathering Melting Melting is the result of continued heating Leads to production of magma and new igneous rocks which are formed when the the magma cools. This process depends on the size of the reservoir that it drains and the relative intensity or activity of plate tectonics. Melting is the result of continued heating Leads to production of magma and new igneous rocks which are formed when the the magma cools. This process depends on the size of the reservoir that it drains and the relative intensity or activity of plate tectonics. Melting Interactives . The Rock Cycle . How Rocks Change How Rocks Change Introduction Does it seem to you that rocks never change? For example, if you find a chunk of granite today, can you expect that it will still be granite at the end of your lifetime? That may well be true — but only because our lifetimes are very short relative to the history of the earth.

If we take a step back to look at geologic time (which focuses on changes taking place over millions of years), we find that rocks actually do change! All rocks, in fact, change slowly from one type to another, again and again. The changes form a cycle, called "the rock cycle." The way rocks change depends on various processes that are always taking place on and under the earth's surface. Now let's take a closer look at each of these processes. Heat & Pressure What happens to cookie dough when you put it in the oven? The heat of the oven produces changes in the ingredients that make them interact and combine. Without melting the dough, the heat changes it into a whole new product — a cookie. A similar process happens to rocks beneath the earth's surface. Due to movements in the crust, rocks are frequently pulled under the surface of the earth, where temperatures increase dramatically the farther they descend. Between 100 and 200 kilometers (62 and 124 miles) below the earth's surface, temperatures are hot enough to melt most rocks. However, before the melting point is reached, a rock can undergo fundamental changes while in a solid state — morphing from one type to another without melting.

An additional factor that can transform rocks is the pressure caused by tons of other rocks pressing down on it from above; heat and pressure usually work together to alter the rocks under the earth's surface. This kind of change, which results from both rising temperature and pressure, is called metamorphism, and the resulting rock is a metamorphic rock. Metamorphic Rocks Definition of Metamorphism The word "Metamorphism" comes from the Greek: Meta = change, Morph = form, so metamorphism means to change form. In geology this refers to the changes in mineral assemblage and texture that result from subjecting a rock to pressures and temperatures different from those under which the rock originally formed. The original rock that has undergone metamorphism is called the protolith. Protolith can be any type of rock and sometimes the changes in texture and mineralogy are so dramatic that is difficult to distinguish what the protolith was. Note that diagenesis and weathering are also a changes in form that occur in rocks.

In geology, however, we restrict diagenetic processes to those which occur at temperatures below 200oC and pressures below about 300 MPa (MPa stands for Mega Pascals), this is equivalent to about 3,000 atmospheres of pressure. Metamorphism therefore occurs at temperatures and pressures higher than 200oC and 300 MPa. Rocks can be subjected to these higher temperatures and pressures as they become buried deeper in the Earth. Such burial usually takes place as a result of tectonic processes such as continental collisions or subduction. The upper limit of metamorphism occurs at the pressure and temperature of wet partial melting of the rock in question. Once melting begins, the process changes to an igneous process rather than a metamorphic process. During metamorphism the protolith undergoes changes in texture of the rock and the mineral make up of the rock. These changes take place mostly in the solid state and are caused by changes in physical or chemical conditions, which in turn can be caused by such things as burial, tectonic stress, heating by magma or interactions with fluids.

Factors that Control Metamorphism Metamorphism occurs because rocks undergo changes in temperature and pressure and may be subjected to differential stress and hydrothermal fluids. Metamorphism occurs because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions. But, the process is complicated by such things as how the pressure is applied, the time over which the rock is subjected to the higher pressure and temperature, and whether or not there is a fluid phase present during metamorphism. Temperature Temperature increases with depth in the Earth along the Geothermal Gradient. Thus higher temperature can occur by burial of rock. Temperature can also increase due to igneous intrusion. Pressure increases with depth of burial, thus, both pressure and temperature will vary with depth in the Earth. Pressure is defined as a force acting equally from all directions. It is a type of stress, called hydrostatic stress, or uniform stress. If the stress is not equal from all directions, then the stress is called a differential stress. Non-foliated rocks lack a planar fabric .

Absence of foliation possible for several reasons: Rock not subjected to differential stress. Dominance of equant minerals (like quartz, feldspar, and garnet). Absence of platy minerals (sheet silicates). Non-foliated rocks are given specific names based on their mineralogy and composition: Amphibolite - These rocks are dark colored rocks with amphibole (usually hornblende) as their major mineral. They are usually poorly foliated and form at intermediate to high grades of metamorphism of basaltic or gabbroic protoliths. Hornfels - These are very fine grained rocks that usually form as a result of magma intruding into fined grained igneous rocks or shales. The magma causes a type of metamorphism called contact metamorphism (to be discussed later). Quartzite - A rock made up almost entirely of quartz. They are formed by metamorphism of quartz arenites (sandstones). Since quartz is stable over a large range of temperatures and pressures, no new minerals are formed during metamorphism, and the only metamorphic effect that occurs is recrystallization of the quartz resulting in interlocking crystals that make up a very hard rock.

Marble - A limestone or dolostone made up only of calcite or dolomite will metamorphose to a marble which is made mostly recrystallized calcite or dolomite. The Recrystallization usually obliterates all fossils. Marbles have a variety of colors and are often complexly banded. They are commonly used as a decorative stone. Protolith Composition Although textures and structures of the protolith are usually destroyed by metamorphism, we can still get an idea about the original rock from the minerals present in the metamorphic rock. Minerals that form, do so because the chemical elements necessary to form them are present in the protolith. General terms used to describe the chemical composition of both the protolith and the resulting metamorphic rock are: Pelitic Alumina rich rocks, usually shales or mudstones. These start out originally with clay minerals and as a result of metamorphism, Alumina rich minerals like micas, chlorite, garnet, kyanite, sillimanite and andalusite form. Because of the abundance of sheet silicates, pelitic rocks commonly form slates, phyllites, schists, and gneisses during metamorphism.

Mafic - These are Mg and Fe rich rocks with low amounts of Si. Minerals like biotite, hornblende and plagioclase form during metamorphism and commonly produce amphibolites. Calcareous - These are calcium-rich rocks usually derived from limestones or dolostones, and thus contain an abundance of Calcite. Marbles are the type of metamorphic rock that results. Quartzo-Feldspathic - Rocks that contain an abundance of quartz and feldspar fall into this category. Protoliths are usually granites, rhyolites, or arkose sandstones and metamorphism results in gneisses containing an abundance of quartz, feldspar, and biotite. Types of Metamorphism Metamorphism can take place in several different environments where special conditions exist in terms of pressure, temperature, stress, conditions, or chemical environments. We here describe several diff rent types of metamorphism that are recognized. Contact Metamorphism (also called thermal metamorphism) - Occurs adjacent to igneous intrusions and results from high temperatures associated with the igneous intrusion.

Since only a small area surrounding the intrusion is heated by the magma, metamorphism is restricted to a zone surrounding the intrusion, called a metamorphic aureole. Outside of the contact aureole, the rocks are unmetamorphosed. The grade of metamorphism increases in all directions toward the intrusion. Because temperature differences between the surrounding rock and the intruded magma are larger at shallow levels in the crust, contact metamorphism is usually referred to as high temperature, low pressure metamorphism. The rock produced is often a fine-grained rock that shows no foliation, called a hornfels. Burial Metamorphism - When sedimentary rocks are buried to depths of several hundred meters, temperatures greater than 300oC may develop in the absence of differential stress. New minerals grow, but the rock does not appear to be metamorphosed. The main minerals produced are the Zeolites. Burial metamorphism overlaps, to some extent, with diagenesis, and grades into regional metamorphism as temperature and pressure increase. Dynamic Metamorphism - This type of metamorphism is due to mechanical deformation, like when two bodies of rock slide past one another along a fault zone.

Heat is generated by the friction of sliding along the zone, and the rocks tend to crushed and pulverized due to the sliding. Dynamic metamorphism is not very common and is restricted to a narrow zone along which the sliding occurred. The rock that is produced is called a mylonite. Regional Metamorphism - This type of metamorphism occurs over large areas that were subjected to high degrees of deformation under differential stress. Thus, it usually results in forming metamorphic rocks that are strongly foliated, such as slates, schists, and gneisses. The differential stress usually results from tectonic forces that produce a compression of the rocks, such as when two continental masses collide with one another. Thus, regionally metamorphosed rocks occur in the cores of mountain ranges or in eroded mountain ranges. Compressive stresses result in folding of the rock, as shown here, and results in thickening of the crust which tends to push rocks down to deeper levels where they are subjected to higher temperatures and pressures (See Figure 8.20 in your text). A map of a hypothetical regionally metamorphosed area is shown in the figure below.

Most regionally metamorphosed areas can be divided into zones where a particular mineral, called an index mineral, is characteristic of the zone. The zones are separated by lines (surfaces in three dimensions) that mark the first appearance of the index mineral. These lines are called isograds (meaning equal grade) and represent lines (really surfaces) where the grade of metamorphism is equal. A map of a regionally metamorphosed areas are can be seen in figure 8.16 of your text. Hydrothermal Metamorphism - Near oceanic ridges where the oceanic crust is broken up by extensional faults, sea water can descend along the cracks. Since oceanic ridges are areas where new oceanic crust is created by intrusion and eruption of basaltic magmas, these water-rich fluids are heated by the hot crust or magma and become hydrothermal fluids. The hydrothermal fluids alter the basaltic oceanic crust by producing hydrous minerals like chlorite and talc. Because chlorite is a green colored mineral the rocks hydrothermal metamorphic rocks are also green and often called greenstones.

Subduction Related Metamorphism - At a subduction zone, the oceanic crust is pushed downward resulting in the basaltic crust and ocean floor sediment being subjected to relatively high pressure. But, because the oceanic crust by the time it subducts is relatively cool, the temperatures in the crust are relatively low. Under the conditions of low temperature and high pressure, metamorphism produces an unusual blue mineral, glaucophane. Compressional stresses acting in the subduction zone create the differential stress necessary to form schists and thus the resulting metamorphic rocks are called blueschist Shock Metamorphism - When a large meteorite collides with the Earth, the kinetic energy is converted to heat and a high pressure shock wave that propagates into the rock at the impact site. The heat may be enough to raise the temperature to the melting temperature of the earth rock. The shock wave produces high enough pressure to cause quartz to change its crystal structure to more a dense polymorph like coesite or stishovite. Ancient meteorite impact sites have been discovered on the basis of finding this evidence of shock metamorphism. Metamorphic Facies In general, metamorphic rocks do not undergo significant changes in chemical composition during metamorphism.

The changes in mineral assemblages are due to changes in the temperature and pressure conditions of metamorphism. Thus, the mineral assemblages that are observed must be an indication of the temperature and pressure environment that the rock was subjected to. This pressure and temperature environment is referred to as Metamorphic Facies. The sequence of metamorphic facies observed in any metamorphic terrain, depends on the geothermal gradient that was present during metamorphism. A high geothermal gradient such as the one labeled "A" in the figure shown here, might be present around an igneous intrusion, and would result in metamorphic rocks belonging to the hornfels facies. Under a normal geothermal gradient, such as "B" in the figure, rocks would progress from zeolite facies to greenschist, amphibolite, and eclogite facies as the grade of metamorphism (or depth of burial) increased. If a low geothermal gradient was present, such the one labeled "C" in the diagram, then rocks would progress from zeolite facies to blueschist facies to eclogite facies.

Thus, if we know the facies of metamorphic rocks in the region, we can determine what the geothermal gradient must have been like at the time the metamorphism occurred. The Rock Cycle Before moving on to the rest of the course, you should read Interlude C in your textbook (pages 261-268). Now that we have discussed the three types of rocks, it is important to understand how the atoms that make up these rocks cycle through the earth. This cycling involves process that will be discussed in detail throughout the remainder of this course. Since the rock cycle links the rock forming processes to tectonic process and to surface process (most of which will be discussed throughout the rest of the course) , it is important to understand the concept of the rock cycle and the various linkages involved. The rock cycle involves cycling of elements between various types of rocks, and thus mostly involves the lithosphere. The rock cycle involves the three types of rocks as reservoirs (1) igneous, (2) sedimentary, and (3) metamorphic. Chemical elements can reside in each type of rock, and geologic processes move these elements into another type of rock.

Energy for the parts of the crustal cycle near the Earth's surface is solar and gravitational energy (which control erosion and weathering), whereas energy that drives processes beneath the surface is geothermal and gravitational energy (which control uplift, subsidence, melting, and metamorphism). We here start our discussion with Volcanoes and Volcanic eruptions and processes that are involved in the production of igneous rocks at the earth's surface. Questions on this material that might be asked on an exam Define the following: (a) geothermal gradient, (b) metamorphism, (c) differential stress, (d) prograde metamorphism, (e) metasomatism (f) protolith, (g) foliation, (i) metamorphic aureole, (j) isograd, (k) greenstone, (l) blueschist. Starting with a shale, describe the textural changes that would occur to the rock during prograde metamorphism with differential stress conditions present. Why is retrograde metamorphism uncommon? Describe the following non-foliated metamorphic rocks (a) amphibolite, (b) quartzite, (c) marble, (d) hornfels.

What are the terms used to describe the general chemical composition of metamorphic rocks?. Describe the type of rocks and minerals four nd in each. What are the various types of metamorphism? Describe the rocks produced by each. What is the progression of metamorphic facies that would occur along a high geothermal gradient, a normal geothermal gradient, and a low geothermal gradient. Metamorphic Rock Formation Transforming Sedimentary Rocks Your Headline Metamorphic Rock Formation from sedimentary rocks is caused by heat and pressure. Where does this heat and pressure come from? The heat and pressure comes from inside the earth. From the upper mantle up to within a few kilometers of the surface of the earth there is a tremendous amount of heat and pressure. This heat and pressure increase with depth. It is estimated that the temperature increases about 20o to 30o C per kilometer of depth. Plate Tectonics Adds Heat And Pressure There is something else that adds to both the heat and pressure, and that is plate tectonics. When the plates of the earth collide, they squeeze the rocks at the borders with unbelievable force. This force increases the pressure in this and surrounding areas. Friction is also created by the plates grinding together.

This friction generates enough heat to melt the rocks at the point of contact. Heat For metamorphism to occur energy is needed to fuel the chemical reactions. Heat is the primary source of this energy. Pressure The pressure within the earth is the result of gravity pulling the crust of the earth downward.Like heat, pressure increases with depth. This pressure can actually squeeze the spaces out of the minerals within the rock. This makes the rocks denser. The heat and pressure together cause the rock to flow instead of break or fracture. The mineral grains become realigned. They flatten out and get longer. Sedimentary rocks exposed to this kind of heat and pressure are transformed into new kinds of rocks. Limestone changes to marble. Shale changes to slate. Metamorphic Rocks Lesson #14 | Volcano World | Oregon State University Home » Earth Science Lessons » Chapter 4 Rocks and Minerals Metamorphic Rocks Lesson #14 Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks form when rocks are heated to the melting point which forms magma .

Sedimentary rocks are formed from the cementing together of sediments, or from the compaction (squeezing together) of sediments, or from the recrystallization of new mineral grains which are larger than the original crystals. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock. The word "metamorphic" comes from Greek and means "To Change Form". The diagram above shows you how the rocks on Earth have been changed continually over time from one rock type to another. This changing of rock types is called the "Rock Cycle". Solid rock can be changed into a new rock by stresses that cause an increase in heat and pressure. There are 3 main agents that cause metamorphism. Factors that cause an increase in Temperature, Pressure, and Chemical changes are the three agents that we are going to study. Temperature increases can be caused by layers of sediments being buried deeper and deeper under the surface of the Earth. As we descend into the earth the temperature increases about 25 degrees Celsius for every kilometer that we descend. The deeper the layers are buried the hotter the temperatures become.

The great weight of these layers also causes an increase in pressure, which in turn, causes an increase in temperature. shearing effect of the plates sliding past each other causes the rocks coming in contact with the descending rocks to change. Some of the descending rock will melt because of this friction. When rock melts it is then considered igneous not metamorphic, but the rock next to the melted rock can be changed by the heat and become a metamorphic rock. The diagram above shows you where metamorphic rock (YELLOW ZONE) can be produced at a subduction zone. There are 3 factors that cause an increase in pressure which also causes the of metamorphic rocks. These factors are; 1. The huge weight of overlying layers of sediments. 2. Stresses caused by plates colliding in the process of mountain building. 3. Stresses caused by plates sliding past each other, such as the shearing stresses at the San Andreas fault zone in California. Factors that cause chemical changes in rocks also contribute to the formation of metamorphic rocks. Very hot fluids and vapors can, because of extreme pressures, fill the pores of existing rocks.

These fluids and vapors can cause chemical reactions to take place, that over time, can change the chemical makeup of the parent rock. Metamorphism can be instantaneous as in the shearing of rocks at plate boundaries or can take millions of years as in the slow cooling of magma buried deep under the surface of the Earth. There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism. Contact Metamorphism occurs when magma comes in contact with an already existing body of rock. When this happens the existing rocks temperature rises and also becomes infiltrated with fluid from the magma. The area affected by the contact of magma is usually small, from 1 to 10 kilometers. Contact metamorphism produces non-foliated (rocks without any ) rocks such as marble, quartzite, and hornfels. In the diagram above magma has pushed its way into layers of limestone, quartz sandstone and shale. The heat generated by the magma chamber has changed these sedimentary rocks into the metamorphic rocks marble, quartzite, an hornfels. Regional Metamorphism occurs over a much larger area. This metamorphism produces rocks such as gneiss and schist.

Regional metamorphism is caused by large geologic processes such as mountain-building. These rocks when exposed to the surface show the unbelievable pressure that cause the rocks to be bent and broken by the mountain building process. Regional metamorphism usually produces foliated rocks such as gneiss and schist. Dynamic Metamorphism also occurs because of mountain-building. These huge forces of heat and pressure cause the rocks to be bent, folded, crushed, flattened, and sheared. Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away. Many metamorphic rocks are found in mountainous regions today and are a good indicator that ancient mountains were present in areas that are now low hill or even flat plains. Metamorphic rocks are divided into two categories- Foliates and Non-foliates. Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock.

Slate, as an example, will split into thin sheets. Foliate comes from the Latin word that means sheets, as in the sheets of paper in a book. Silt and clay can become deposited and compressed into the sedimentary rock shale. The layers of shale can become buried deeper and deeper by the process of deposition. Deposition is the laying down of rock forming material by any natural agent (wind, water, glaciers) over time. Because these layers are buried, temperatures and pressures become greater and greater until the shale is changed into slate. Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown . Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures. Slate has been used by man in a variety of ways over the years. One use for slate was in the making of headstones or grave markers. Slate is not very hard and can be carved easily. The problem with slate though is its perfect cleavage. The slate headstones would crack and split along these cleavage planes as water would seep into the cracks and freeze which would lead to expansion.

This freeze-thaw, freeze-thaw over time would split the headstone. Today headstones are made of a variety of rocks, with granite and marble being two of the most widely used rocks. Slate was also used for chalk boards. The black color was good as a background and the rock cleaned easily with water. Today it is not very advantageous to use this rock because of its weight and the splitting and cracking over time. Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye. Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main minerals that they are formed from. Bitotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this. Gneiss is a high grade metamorphic rock.

This means that gneiss has been subjected to more heat and pressure than schist. Gneiss is coarser than schist and has distinct banding. This banding has alternating layers that are composed of different minerals. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite. Gneiss can be used by man as paving and building stone. Non-Foliates are metamorphic rocks that have no cleavage at all. Quartzite and marble are two examples of non-foliates that we are going to study. Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock. The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains.

Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate (CaCO3). Marble has many different sizes of crystals. Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green. Marble is much harder than its parent rock. This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists. Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges. Marble is quarried in Vermont, Tennessee, Missouri, Georgia, and Alabama. Write the answers to the following questions in complete sentences on a piece of paper. 1. Write a definition in your own words of what a metamorphic rock is. 2. What are the three agents of metamorphism? 3. What are the three types of metamorphism? 4.

How Rocks Form: Igneous Rocks, Sedimentary Rocks, Metamorphic Rocks | Online Homework Help | SchoolWorkHelper How Rocks Form: Igneous Rocks, Sedimentary Rocks, Metamorphic Rocks You are here: PDF Why study rocks? -Many, many uses! – writing tools (chalk, pencils), building materials (marble, concrete), fuels (coal), scouring powder (pumice, sand), weapons (flint, obsidian) Rock: a group of minerals bound together – found in the Earth’s crust and mantle The Rock Cycle: the continuous process of rock formation and change – Presents a “map" of the basic processes, the transformation of rock from one form to another. Many variations!! – These rocks are classified according to their origins, or processes by which they formed: 1. igneous rocks: formed by the cooling and hardening of magma (molten rock) from inside Earth 2. sedimentary rocks: formed by the compaction and cementing of layers of sediment (rock fragments, plant and animal remains, minerals from water) 3.

metamorphic rocks: formed by the effect of heat and pressure on other rocks Igneous Rocks *Earth’s crust is made-up primarily of igneous rocks. *Classified according to composition and texture. –Composition determined by the type of magma from which it formed. –Texture determined by rate at which the magma cooled. 2 main types of magma (plus intermediate): 1. felsic– thick; slow-moving; large amounts of silica (SiO2); light-colored silicate rocks (contain mainly quartz and feldspar) 2. mafic– hotter; thinner; faster-moving; low amounts of silica (SiO2); dark-colored rocks (contain mainly hornblende, augite, biotite) 3 main rates at which magma cools and hardens: 1. Magma trapped inside the Earth’s crust hardens very slowly to form intrusive igneous rocks. –Pluton: a rock mass underground that forms from the magma cooling there. –Batholith: largest of all plutons that forms the cores of many mountains -These rocks only appear on Earth after they are pushed up and the overlying rock is worn away.

-granular, coarse-grained texture; larger crystals (because magma is cooling slowly, giving crystals time to form and “grow") -examples: gabbro, granite 2. Magma that pours onto Earth’s surface (lava) hardens very quickly to form extrusive igneous rocks. -smoother, fine-grained, to glassy texture; microscopic crystals or no crystals at all (because magma is cooling quickly giving crystals very little time to form) -examples: obsidian, basalt, pumice, rhyolite 3. Sometimes, magma that’s trapped inside the Earth and begins cooling slowly, can then be suddenly forced to the surface and finish cooling quickly. This forms porphyritic igneous rocks. -large crystals surrounded by a fine-grained mass of rock. (2 different textures) Sedimentary Rocks *Most of the Earth’s surface is covered by sedimentary rocks. *Classified by formation process and particle size. 3 basic formation processes: 1. clastic rocks– formed from fragments of other rocks. How does this happen? a. A river moves sediments into a body of water. b. Particles are sorted by size.

Largest, heaviest stones are deposited first, followed by sands, and finally silts and clays. c. Over time, the sediments are buried and compacted and may become cemented together. –cementation: process during which loose sediments become bound together by natural cements -Influences a rock’s color. d. -Larger particles form conglomerates; coarsest texture of clastic rock -Sands form sandstone; rough, gritty texture -Silt and clay form shale; smooth, soft, easily broken (p.128) 2. chemical rocks– formed from chemical sediments that precipitate out of water –Geodes form in this way! (sphere of silica rock filled with crystals) -other examples: rock salt (halite), some limestones 3. organic rocks– formed from sediments made-up of the remains of plants and animals (clam shells, coral, bone) -examples: coal, limestone, coquina Sedimentary rocks contain 3 distinct features: stratification: change in the type of sediment being laid down produces stripes or visible layers of rock The single most characteristic feature, common in most sedimentary rocks!

fossils: the remains, or impressions, of a plant or animal preserved in rock ripple marks and mud cracks: sand patterns formed by wind or water, and/or cracks caused by the drying and contracting of sediments Metamorphic Rocks *Formed from preexisting rocks called parent rocks. *Metamorphism: process by which a rock’s structure is changed by pressure and heat –Pressure comes from the great weight of overlying rocks; Also from plate movement. –Heat comes from inside the Earth. Effects of metamorphism on rocks: 1. affects chemical composition– new minerals may appear 2. affects texture– rock could become smoother or coarser 3. affects internal structure– minerals may be enlarged or re-formed; pressure may force grains to flatten, stretch, and/or become more compact -Often, metamorphosized rocks will become foliated: form bands of minerals or split along parallel lines -Examples: sandstone (sed.) > quartzite Metamorphic Rocks Metamorphic Rocks Metamorphic rocks can be formed from any rock type: igneous, sedimentary, or existing metamorphic rocks. Involves recrystallization in the solid state, often with little change in overall chemical composition.

Driving forces are changes in temperature, pressure, and pore fluids. New minerals and new textures are formed. During metamorphism platy minerals grow in the direction of least stress producing foliation. Rocks with only one, non-platy, mineral produce nonfoliated rocks such as quartzite or marble. Two types of metamorphism: contact and regional. Foliated rocks - slate, phyllite, schist, gneiss, mylonite Non-foliated rocks - quartzite, marble, hornfels, greenstone, granulite Mineral zones are used to recognize metamorphic facies produced by systematic pressure and temperature changes. Origin of Metamorphic Rocks Below 200oC rocks remain unchanged. As temperature rises, crystal lattices are broken down and reformed with different combinations of atoms. New minerals are formed. The mineral composition of a rock provides a key to the temperature of formation (Fig. 6.5) Where does the heat come from? Hot magma ranges from 700-12000C. Causes contact metamorphism. Deep burial - temperature increases 15-300C for every kilometer of depth in the crust.

Subduction and continental collision bury rocks to depths of 10s of kms. This is regional metamorphism. Most metamorphic rocks form this way. Pressure Hydrostatic pressure - produced by the weight of overlying rocks. Directed pressure - lateral forces produced by plate tectonics. Directed pressure produces the foliation in regionally metamorphosed rocks. Chemically Active Fluids Metasomatism - fluid transport during metamorphism can result in the gain or loss of atoms. Clays release H2O (de-watering) as they change to minerals such as kyanite or garnet. Hydrothermal alteration - injection of hot water into rocks from metasomatism can produce metallic ores such as lead and zinc. Chemically Active Fluids Seafloor metamorphism - ocean water heated by contact metamorphism is a form of metasomatism. This converts the olivine and pyroxene in basalt into hydrated silicates such as serpentine, chlorite, and talc. This changes basalt to greenstone. Textures of Metamorphic Rocks Foliated (Latin for leaf) - grades from slate to phyllite to schist to gneiss. Produced by platy minerals growing in direction of least stress.

Nonfoliated - typical when parent rock is sandstone or limestone. Also occurs in contact metamorphism and extreme metamorphism (granulite facies). Mylonitic - formed along faults; rare. Kinds of Metamorphic Rocks Slate - low grade metamorphosed shale; very fine grained; slaty cleavage should not be confused with bedding planes. Phyllite - next step up from slate, larger mica grains give the rock a luster. Schist - a strongly foliated rock with large grains of platy minerals. Named for its minerals; e.g., chlorite schist. Kinds of Metamorphic Rocks Gneiss - a coarse grained granular rock in which foliation results from alternating layers of light and dark minerals. Compositionally similar to granite with quartz, feldspar, biotite, and amphibole. Forms during regional high grade metamorphism. May grade into migmatite and even granite. Parent rock and type of gneiss: granite biotite becomes gneiss Regional Metamorphic Zones Mineral zones reflect differences in metamorphic grade across a region. Geologists map metamorphic zones based on mineral changes. Used to locate central vs. marginal parts of ancient mountain belts.

Index minerals in order: chlorite, biotite, garnet, staurolite, kyanite, sillimanite. Metamorphic Facies Granulite facies - high grade metamorphic rocks; characteristic minerals are pyroxene, sillimanite, and garnet. Close to melting point, migmatite often present. Blueschist facies - a high pressure, low temperature facies; color from blue amphibole Eclogite facies - very high pressure (upper mantle) and temperature; pyroxene and garnet Metamorphic Rocks and Plate Tectonics Greenschist facies - upper continental crust in mountain ranges, and seafloor metamorphism of basalt Amphibolite and granulite facies - form progressively deeper in the roots of mountains Contact metamorphic rocks - form near igneous intrusions in mountain ranges Metamorphic Rocks and Plate Tectonics Blueschist facies - shallow part of subduction zone Eclogite facies - deeper part of subduction zone and upper mantle

Question: What kind of rock is formed as a result of heat or pressure?
Answer: Metamorphic Rock