More technically, foliation is any penetrative planar fabric present in metamorphic rocks. . A special type of metamorphism takes place under these very high-pressure but relatively low-temperature conditions, producing an amphibole mineral known as glaucophane (Na2(Mg3Al2)Si8O22(OH)2). With aligned minerals that are coarse enough to see, rocks that exhibit schistose foliation sparkle, because they contain micas that reflect light. It is composed primarily of calcium carbonate. Meg Schader is a freelance writer and copyeditor. The large boulder in Figure 10.8 in has strong foliation, oriented nearly horizontally in this view, but it also has bedding still visible as dark and light bands sloping steeply down to the right. The pattern of aligned crystals that results is called foliation. 1 Earth Sciences 1023/2123 Lab #2 Rocks, the Rock Cycle and Rock Identification Introduction: This lab introduces the basics of geology, including rock types, their origins and their identification. Usually, this represents the protolith chemistry, which forms distinct mineral assemblages. This effect is especially strong if the new minerals are platy like mica or elongated like amphibole. Foliation is usually formed by the preferred orientation of minerals within a rock. Minerals are homogeneous, naturally occurring inorganic solids. Preface to the First University of Saskatchewan Edition, Second University of Saskatchewan Edition: Goals, 1.4 We Study Earth Using the Scientific Method, 1.5 Three Big Ideas: Geological Time, Uniformitarianism, and Plate Tectonics, 2.2 Forming Planets from the Remnants of Exploded Stars, 3.1 Earth's Layers: Crust, Mantle, and Core, 4.1 Alfred Wegener's Arguments for Plate Tectonics, 4.2 Global Geological Models of the Early 20th Century, 4.3 Geological Renaissance of the Mid-20th Century, 4.4 Plates, Plate Motions, and Plate-Boundary Processes, 8.3 Controls on Weathering Processes and Rates, 8.4 Weathering and Erosion Produce Sediments, 9.2 Chemical and Biochemical Sedimentary Rocks, 9.4 Depositional Environments and Sedimentary Basins, 10.4 Types of Metamorphism and Where They Occur, 10.5 Metamorphic Facies and Index Minerals, 10.6 Metamorphic Hydrothermal Processes and Metasomatism, 11.2 Materials Produced by Volcanic Eruptions, 11.7 Monitoring Volcanoes and Predicting Eruptions, 12.5 Forecasting Earthquakes and Minimizing Impacts, 15.1 Factors That Control Slope Stability, 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting, 18.1 If You Can't Grow It, You Have to Mine It, Appendix A. Textures Non-foliated or granular metamorphic rocks are those which are composed of equi-dimensional grains such as quartz or calcite. If stress from all directions is equal, place all thin arrows. She holds a Bachelor of Science in agriculture from Cornell University and a Master of Professional Studies in environmental studies from SUNY College of Environmental Science and Forestry. A rock with visible minerals of mica and with small crystals of andalusite. Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth's surface. The passage of this water through the oceanic crust at these temperatures promotes metamorphic reactions that change the original olivine and pyroxene minerals in the rock to chlorite ((Mg5Al)(AlSi3)O10(OH)8) and serpentine ((Mg,Fe)3Si2O5(OH)4). You can help Wikipedia by expanding it. Considering that the normal geothermal gradient (the rate of increase in temperature with depth) is around 30C per kilometer in the crust, rock buried to 9 km below sea level in this situation could be close to 18 km below the surface of the ground, and it is reasonable to expect temperatures up to 500C. Metamorphic rocks are rocks that have been changed either in texture or in mineral composition by the influence of heat, pressure, stress (directed pressure), chemically active solutions or gasses or some other agent without the rock passing through a liquid phase. Essentially, the minerals are randomly oriented. [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. These rocks are all foliated because of the strong compressing force of the converging plates. The specimen shown above is about two inches (five centimeters) across. [1] It is caused by shearing forces (pressures pushing different sections of the rock in different directions), or differential pressure (higher pressure from one direction than in others). mineral cleavage. Metamorphism and Metamorphic Rocks, Chapter 17: Humans' Relationship to Earth Processes, Physical Geology, First University of Saskatchewan Edition, Next: 6.5 Metamorphic Facies and Index Minerals, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Similarly, a gneiss that originated as basalt and is dominated by amphibole, is an amphibole gneiss or, more accurately, an amphibolite. Chapter 6. (PDF) Petrostructural Features of Metaconglomerate in Igarra and Otuo, South-Western Nigeria Petrostructural Features of Metaconglomerate in Igarra and Otuo, South-Western Nigeria Authors:. At higher pressures and temperatures, grains and crystals in the rock may deform without breaking into pieces (Figure 6.34, left). Essentially, the minerals are randomly oriented. The rock in the upper left of Figure 10.9 is foliated, and the microscopic structure of the same type of foliated rock is shown in the photograph beneath it. Block-in-matrix structures are observed in these exposures, including a large metaconglomerate block (10s m in diameter) found at . Most of the blueschist that forms in subduction zones continues to be subducted. Foliated metamorphic rocks have elongated crystals that are oriented in a preferred direction. The location of the wings depends on the distribution of stress on the rock (Figure 10.10, upper right). After both heating and squeezing, new minerals have formed within the rock, generally parallel to each other, and the original bedding has been largely obliterated. When describing a foliation it is useful to note. Rocks that form from regional metamorphism are likely to be foliated because of the strong directional pressure of converging plates. The figure below shows a metaconglomerate. Observing foliation - "compositional banding", Assess foliation - foliated vs non-foliated, Compare non-foliated (massive) and foliated, (Contact Scott Brande) mailto:soskarb@gmail.com. Contact metamorphism happens when a body of magma intrudes into the upper part of the crust. Metamorphic differentiation, typical of gneisses, is caused by chemical and compositional banding within the metamorphic rock mass. Quartzite: Formed by the metamorphism of pure quartz sandstone. Gold prospectors learned that gold could be found in areas where these green rocks were present. For rocks at the surface, the true starting point for the rock cycle would be (a) igneous (b) sedimentary (c) metamorphic. Dynamic metamorphism occurs at relatively low temperatures compared to other types of metamorphism, and consists predominantly of the physical changes that happen to a rock experiencing shear stress. 2011 Richard Harwood | profharwood@icloud.com | Home. Granofels is a broad term for medium- to coarse-grained metamorphic rocks that do not exhibit any specific foliation. It is composed primarily of hornblende (amphibole) and plagioclase, usually with very little quartz. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. If the original rock had bedding (represented by diagonal lines in Figure 10.7, right), foliation may obscure the bedding. Figure 10.24 Metaconglomerate formed through burial metamorphism. . The quartz crystal in Figure 6.32 has two sets of these lines. . As already noted, slate is formed from the low-grade metamorphism of shale, and has microscopic clay and mica crystals that have grown perpendicular to the stress. Soapstone is a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes, and carbonates. If a rock is buried to a great depth and encounters temperatures that are close to its melting point, it will partially melt. To the unaided eye, metamorphic changes may not be apparent at all. The growth of platy minerals, typically of the mica group, is usually a result of prograde metamorphic reactions during deformation. The mineral alignment in the metamorphic rock called slate is what causes it to break into flat pieces (Figure 10.12, left), and is why slate has been used as a roofing material (Figure 10.12, right). Metaconglomerate: Non-foliated: Metamorphism of conglomerate: Metamorphic Rock . Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. Introduction to Hydrology and Rivers, 11a. EARTH SCIENCE LAB Metamorphic Sample #1: Identify the Texture, Foliation, Composition, Parent Rock and Rock Type Metamorphic Rock Identification Chart FOLIATION COMPOSITION PARENT ROCK ROCK NAME TEXTURE Oslaty O mica Mudstone O phyllitic O quartz, mica, chlorite O Mudstone O Foliated Omica, quartz O Slate O schistose amphibole, plagioclase O In the example shown in Figure 7.8d, the dark bands are largely amphibole while the light-coloured bands are feldspar and quartz. Two features of shock metamorphism are shocked quartz, and shatter cones. Most people are surprised to learn that, so we added it to this photo collection as a surprise. Metamorphic rock may exhibit a variety of features related to the organization and arrangement of its component materials. Heat is important in contact metamorphism, but pressure is not a key factor, so contact metamorphism produces non-foliated metamorphic rocks such as hornfels, marble, and quartzite. Non-foiliated - those having homogeneous or massive texture like marble. The rock also has a strong slaty foliation, which is horizontal in this view, and has developed because the rock was being squeezed during metamorphism. METACONGLOMERATE The parent rock for metaconglomerate is the sedimentary rock . As we're confining our observation to samples without visual aids, we may be subject to some error of identification. In the formation of schist, the temperature has been hot enough so that individual mica crystals are visible, and other mineral crystals, such as quartz, feldspar, or garnet may also be visible. It is a soft, dense, heat-resistant rock that has a high specific heat capacity. Metamorphic rocks can be foliated, displaying banding or lamellar texture, or non-foliated. Principles of Earth Science by Katharine Solada and K. Sean Daniels is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. takes place at cool temperatures but high pressure. 2. Think of foliated rocks as something that is foiled. Thermal metamorphism in the aureole of a granite is also unlikely to result in the growth of mica in a foliation, although the growth of new minerals may overprint existing foliation(s). This means that slate breaks into thin layers, which have economic value as tiles and blackboards. Often this foliation is associated with diagenetic metamorphism and low-grade burial metamorphism. One such place is the area around San Francisco. The fractures are nested together like a stack of ice-cream cones. foliated metamorphic describes the texture of metamorphic rock Related questions What are some example names of foliated and un-foliated rocks? If you happen to be in the market for stone countertops and are concerned about getting a natural product, it is best to ask lots of questions. In this simplified treatment, we'll focus on observational features, rather than interpretations of origin. Marble is composed of calcite and will readily react to a small drop of HCl. In some cases, hornfels has visible crystals of minerals like biotite or andalusite. The quartz crystals were subjected to the same stress as the mica crystals, but because quartz grows in blocky shapes rather than elongated ones, the crystals could not be aligned in any one direction. The protolith for quartzite is quartz, and because quartz is stable under high pressure and high temperatures, metamorphism of this rock simply causes the reorganization of its crystals. When metamorphosed ocean crust is later subducted, the chlorite and serpentine are converted into new non-hydrous minerals (e.g., garnet and pyroxene) and the water that is released migrates into the overlying mantle, where it contributes to melting. The quartz crystals show no alignment, but the micas are all aligned, indicating that there was directional pressure during regional metamorphism of this rock. The protolith for slate is shale, and sometimes fossils that were present in the original rock can be seen in freshly sheared layers of slate. There are two main types of metamorphism: There are two types of textures on metamorphic rocks: Think of foliated rocks as something that is foiled. Materials in metamorphic rock (e.g., minerals, crystals, clasts) may exhibit orientations that are relatively random or preferred (aligned). This means that the minerals in the rock are all aligned with each other. Notice the sequence of rocks that from, beginning with slate higher up where pressures and temperatures are lower, and ending in migmatite at the bottom where temperatures are so high that some of the minerals start to melt. Foliated - those having directional layered aspect of showing an alignment of particles like gneiss. The tendency of slate to break into flat pieces is called slaty cleavage. Foliated textures show a distinct planar character. Even though the quartz crystals themselves are not aligned, the mass of quartz crystals forms a lens that does follow the general trend of alignment within the rock. Rockman's metamorphic rock specimens are hand broken as opposed to being crushed which helps keep cleavage and fracture characteristics intact. Molecular Biology and Genetics. The zone in the photomicrograph outlined with the red dashed line is different from the rest of the rock. Further identification of non-foliated rocks is dependent on the composition of the minerals or components in the rock. Schist and gneiss can be named on the basis of important minerals that are present. The specimen shown above is a "chlorite schist" because it contains a significant amount of chlorite. Both are black in color , and is composed of carbon. When it forms, the calcite crystals tend to grow larger, and any sedimentary textures and fossils that might have been present are destroyed. lineation - a parallel arrangement of pebbles in a metaconglomerate foliation - a segregation of felsic and mafic minerals into alternating layers as in gneiss. Anthracite coal is similar to bituminous coal. The lower temperatures exist because even though the mantle is very hot, ocean lithosphere is relatively cool, and a poor conductor of heat. Metaconglomerate. This means that the minerals in the rock are all aligned with each other. In sheared zones, however, planar fabric within a rock may . Notice: Unless otherwise noted, all images and graphics contained within are the property of Richard Harwood and may only be reproduced with permission from the author. The stress that produced this pattern was greatest in the direction indicated by the black arrows, at a right angle to the orientation of the minerals. The specimen shown above is about two inches (five centimeters) across. Quartz has a hardness of 7, which makes it difficult to scratch. The outcome of prolonged dynamic metamorphism under these conditions is a rock called mylonite, in which crystals have been stretched into thin ribbons (Figure 6.34, right). Some examples of non-foliated metamorphic rocks are marble, quartzite, and hornfels. Igneous rocks can become foliated by alignment of cumulate crystals during convection in large magma chambers, especially ultramafic intrusions, and typically plagioclase laths. The Origin of Earth and the Solar System, Chapter 8. When extraterrestrial objects hit Earth, the result is a shock wave. The force of the collision causes rocks to be folded, broken, and stacked on each other, so not only is there the squeezing force from the collision, but from the weight of stacked rocks. Foliation in areas of shearing, and within the plane of thrust faults, can provide information on the transport direction or sense of movement on the thrust or shear. This is not always the case, however. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. Unlike slate and phyllite, which typically only form from mudrock, schist, and especially gneiss, can form from a variety of parent rocks, including mudrock, sandstone, conglomerate, and a range of both volcanic and intrusive igneous rocks. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. This forms planes of weakness, and when these rocks break, they tend to break along surfaces that parallel the orientation of the aligned minerals (Figure 10.11). So its parent rock is a conglomerate. In contrast, nonfoliated metamorphic rocks do not contain minerals that align during metamorphism and do not appear layered. Chapter 6 Sediments and Sedimentary Rocks, Chapter 21 Geological History of Western Canada, Next: 7.3 Plate Tectonics and Metamorphism, Creative Commons Attribution 4.0 International License. Over all, the photomicrograph shows that the rock is dominated by elongated crystals aligned in bands running from the upper left to the lower right. Non-foliated textures are identified by their lack of planar character. Foliated textures show a distinct planar character. Most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress. When a rock is acted upon by pressure that is not the same in all directions, or by shear stress (forces acting to smear the rock), minerals can become elongated in the direction perpendicular to the main stress. A rock list of types of foliated metamorphic specimens includes gneiss, schist, phyllite and slate. The specimen above is about two inches (five centimeters) across. Nonfoliated metamorphic rocks are typically formed in the absence of significant differential pressure or shear. Place the thick arrows in the direction of maximum stress and the thin arrows in the direction of minimum stress. The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well. Examples of foliated rocks include: gneiss, phyllite, schist, and slate. Shocked quartz (Figure 6.32 left) refers to quartz crystals that display damage in the form of parallel lines throughout a crystal. As already noted, the nature of the parent rock controls the types of metamorphic rocks that can form from it under differing metamorphic conditions. Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. Foliation Supplying quality educational materials for teachers, collectors and other educational organizations since 1995. Massive (non-foliated) structure. Water within the crust is forced to rise in the area close to the source of volcanic heat, drawing in more water from further away. Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. Sedimentary rocks have been both thrust up to great heightsnearly 9 km above sea leveland also buried to great depths. Metamorphic rocks are rocks that have undergone a change from their original form due to changes in temperature, pressure or chemical alteration. Usually, this is the result of some physical force and its effect on the growth of minerals. - Examples: quartzite derived from the metamorphism of sandstone, and marble derived from the metamorphism of limestone or dolostone. Anthracite is the highest rank of coal. Marble and hornfels are metamorphic rock types that typically do not typically show observable foliation. Partial melting occurs when the temperature on a rock is high enough to melt only some of the minerals in the rock. If the original limestone was pure calcite, then the marble will likely be white (as in Figure 7.10), but if it had various impurities, such as clay, silica, or magnesium, the marble could be marbled in appearance. The kinds of rocks that can be expected to form at different metamorphic grades from various parent rocks are listed in Table 7.1. In geology, key terms related to metamorphic rocks include foliated and nonfoliated. Quartzite is composed of quartz sand grains. Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet. Determination of this information is not easily accomplished in this lab. Whether you need help solving quadratic equations, inspiration for the upcoming science fair or the latest update on a major storm, Sciencing is here to help. Foliation, as it forms generally perpendicular to the direction of principal stress, records the direction of shortening. Texture is divided into two groups. Often, retrograde metamorphism will not form a foliation because the unroofing of a metamorphic belt is not accompanied by significant compressive stress. Examples of nonfoliated metamorphic rocks include marbles, quartzites and soapstones. Metamorphic rock that does not appear to exhibit aligned material to the naked eye may show structure at the microscopic level. Introduction to Geology of the Oceans, 17a Introduction to Human Relationships with Earth Processes. The specimen shown above is about two inches (five centimeters) across. Schistose foliation is composed of larger minerals which are visible to the unaided eye. Some types of metamorphic rocks, such as quartzite and marble, which also form in directed-pressure situations, do not necessarily exhibit foliation because their minerals (quartz and calcite respectively) do not tend to show alignment (see Figure 7.12).
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