Slaty cleavage is composed of platy minerals that are too small to see. The resulting rock, which includes both metamorphosed and igneous material, is known as a migmatite (Figure 7.9). Metaconglomerate looks similar to conglomerate, although sometimes the clasts are deformed. Skarn is a rock characterized by its formation rather than its mineral composition. If a foliation does not match the observed plunge of a fold, it is likely associated with a different deformation event. Foliated - those having directional layered aspect of showing an alignment of particles like gneiss. Labels may be used only once. It has a bright, lustrous appearance and breaks with a semi-conchoidal fracture. The specimen shown above is about two inches (five centimeters) across. Question 14. 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). The best way to learn about rocks is to have a collection of specimens to examine while you study. 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. Some types of metamorphism are characteristic of specific plate tectonic settings, but others are not. Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth's surface. Learn how BCcampus supports open education and how you can access Pressbooks. Slate exhibits slaty foliation, which is also called cleavage. Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. Although bodies of magma can form in a variety of settings, one place magma is produced in abundance, and where contact metamorphism can take place, is along convergent boundaries with subduction zones, where volcanic arcs form (Figure 6.31). Sedimentary rocks have been both thrust up to great heightsnearly 9 km above sea leveland also buried to great depths. Provide reasonable names for the following metamorphic rocks: Physical Geology by Steven Earle is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. These are the result of quartz . The rock in the upper left of Figure 6.9 is foliated, and the microscopic structure of the same type of foliated rock is shown in the photograph beneath it. In sheared zones, however, planar fabric within a rock may not be directly perpendicular to the principal stress direction due to rotation, mass transport, and shortening. Volatiles may exsolve from the intruding melt and travel into the country rock, facilitating heating and carrying chemical constituents from the melt into the rock. Meg Schader is a freelance writer and copyeditor. Observing foliation - "compositional banding", Assess foliation - foliated vs non-foliated, Compare non-foliated (massive) and foliated, (Contact Scott Brande) mailto:soskarb@gmail.com. In this treatment, we'll describe metamorphic rock that does not show visible alignment of materials as massive. While these terms might not provide accurate information about the rock type, they generally do distinguish natural rock from synthetic materials. Polymict metaconglomeraat, . [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. Photographs and brief descriptions of some common types of metamorphic rocks are shown on this page. Anthracite coal is generally shiny in appearance and breaks with a conchoidal fracture (broken glass also shows this type of fracture). Anthracite coal is similar to bituminous coal. For rocks at the surface, the true starting point for the rock cycle would be (a) igneous (b) sedimentary (c) metamorphic. Introduction to Geology of the Oceans, 17a Introduction to Human Relationships with Earth Processes. Seeing and handling the rocks will help you understand their composition and texture much better than reading about them on a website or in a book. Territories. The rock in Figure 10.10 had a quartz-rich conglomerate as a parent rock. It is dominated by quartz, and in many cases, the original quartz grains of the sandstone are welded together with additional silica. In sheared zones, however, planar fabric within a rock may . . Protolith Basalt Conglomerate Dolostone Limestone Granite Sandstone Shale Metamorphic rock Amphibolite Gneiss Marble Metaconglomerate Quartzite Slate Basalt-Amphibolite It is a soft, dense, heat-resistant rock that has a high specific heat capacity. It is a rock of intermediate metamorphic grade between phyllite and gneiss. > The cement between the clasts is recrystallized, so the rock breaks across the clasts (instead of around the clasts in a sedimentary conglomerate). takes place at cool temperatures but high pressure. The Origin of Earth and the Solar System, Chapter 8. This planar character can be flat like a piece of slate or folded. This is not always the case, however. It is foliated, crenulated, and fine-grained with a sparkly appearance. Introduction to Hydrology and Rivers, 11a. The deeper rocks are within the stack, the higher the pressures and temperatures, and the higher the grade of metamorphism that occurs. Not only is the mineral composition differentit is quartz, not micabut the crystals are not aligned. In contrast, nonfoliated metamorphic rocks do not contain minerals that align during metamorphism and do not appear layered. Well foliated to nearly massive quartz monzonite gneiss, generally medium-grained and even textured but locally porphyritic and pegmatitic. Learn more about how Pressbooks supports open publishing practices. The intense heat and pressure of metamorphism . Marble: A non-foliated metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet. Foliations, in a regional sense, will tend to curve around rigid, incompressible bodies such as granite. Any type of magma body can lead to contact metamorphism, from a thin dyke to a large stock. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks. The round objects in the photo are lapis lazuli beads about 9/16 inch (14 millimeters) in diameter. 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). Glaucophane is blue, and the major component of a rock known as blueschist. Gneissic banding is the easiest of the foliations to recognize. 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. There is no evidence of foliation. Rocks that form from regional metamorphism are likely to be foliated because of the strong directional pressure of converging plates. With wavy layering known as phyllitic foliation, these rocks often have a silky or satiny sheen, which is caused by the arrangement of very fine minerals that form as a result of the pressure applied during metamorphism. Chapter 6. It can refer to green mica minerals, or metamorphic rocks that contain enough green mica to impart a green color. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. Created by unique combinations of minerals and metamorphic conditions, these rocks are classified by their chemical compositions. [http://commons.wikimedia.org/wiki/ File:Migmatite_in_Geopark_on_Albertov.JPG] Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. Foliated textures show a distinct planar character. [2], The metaconglomerates of the Jack Hills of Western Australia are the source rocks for much of the detrital zircons that have been dated to be as old as 4.4 billion years.[3][4]. On the other hand, any clay present in the original sandstone is likely to be converted to mica during metamorphism, and any such mica is likely to align with the directional pressure. Most people are surprised to learn that, so we added it to this photo collection as a surprise. The zone in the photomicrograph outlined with the red dashed line is different from the rest of the rock. At lower pressures and temperatures, dynamic metamorphism will have the effect of breaking and grinding rock, creating cataclastic rocks such as fault breccia (Figure 6.33). Hornfels is another non-foliated metamorphic rock that normally forms during contact metamorphism of fine-grained rocks like mudstone or volcanic rock (Figure 7.13). Therefore, a simplified system is used based on texture and composition. In gneiss, the minerals may have separated into bands of different colours. 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. Phyllite is a foliated metamorphic rock that is made up mainly of very fine-grained mica. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. 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. Texture is divided into two groups. In geology, key terms related to metamorphic rocks include foliated and nonfoliated. Partial melting occurs when the temperature on a rock is high enough to melt only some of the minerals in the rock. Massive (non-foliated) structure. In gneiss, the foliation is more typically represented by compositional banding due to segregation of mineral phases. The type and intensity of the metamorphism, and width of the metamorphic aureole that develops around the magma body, will depend on a number of factors, including the type of country rock, the temperature of the intruding body, the size of the body, and the volatile compounds within the body (Figure 6.30). Most of the blueschist that forms in subduction zones continues to be subducted. Similarly, a gneiss that originated as basalt and is dominated by amphibole, is an amphibole gneiss or, more accurately, an amphibolite. Minerals are homogeneous, naturally occurring inorganic solids. 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. The surface of phyllite is typically lustrous and sometimes wrinkled. 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. The low-grade metamorphism occurring at these relatively low pressures and temperatures can turn mafic igneous rocks in ocean crust into greenstone (Figure 6.27), a non-foliated metamorphic rock. The sudden change associated with shock metamorphism makes it very different from other types of metamorphism that can develop over hundreds of millions of years, starting and stopping as tectonic conditions change. Foliations typically bend or curve into a shear, which provides the same information, if it is of a scale which can be observed. Typically, these rocks split along parallel, planar surfaces. Schist and gneiss can be named on the basis of important minerals that are present. [1], Foliated metaconglomerate is created under the same metamorphic conditions that produce slate or phyllite, but with the parent rock (protolith) being conglomerate, rather than clay. In geotechnical engineering a foliation plane may form a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) Foliation can develop in a number of ways. The pattern of aligned crystals that results is called foliation. Quartzite is composed of quartz sand grains. Any rock that contains more than one kind of mineral can be the protolith for gneiss, which is the name for a metamorphic rock that exhibits gneissic banding. Crenulation cleavage and oblique foliation are particular types of foliation. A fourth type of foliated metamorphic rock is called slate. 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. Protoliths are transformed chemically and physically by high temperatures, high pressures, hot fluids or some combination of these conditions. Rockman's metamorphic rock specimens are hand broken as opposed to being crushed which helps keep cleavage and fracture characteristics intact. Schist is a metamorphic rock with well-developed foliation. 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. That means it will take a long time to heat up, can be several hundreds of degrees cooler than the surrounding mantle. It is a low-grade metamorphic rock that splits into thin pieces. Mariposite is a word that has been used in many ways. The metaconglomerate formed through burial metamorphism does not display any of the foliation that has developed in the metaconglomerate in Figure 6.10. Metaconglomerate is composed of pebbles and gravel that have been flattened due to directed pressure. Quartzite: Formed by the metamorphism of pure quartz sandstone. This large boulder has bedding still visible as dark and light bands sloping steeply down to the right. . 2. It is composed primarily of quartz. The Himalaya range is an example of where regional metamorphism is happening because two continents are colliding (Figure 6.25). metaconglomerate - metamorphosed conglomerate ; marble - metamorphosed limestone ; hornfels - contact metamorphism of shale; very hard, like a brick ; . Geologic unit mapped in Maryland: Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet. To the unaided eye, metamorphic changes may not be apparent at all. Thus, they are not always 'planar' in the strictest sense and may violate the rule of being perpendicular to the regional stress field, due to local influences. Types of Foliated Metamorphic Rocks Following such a methodology allows eventual correlations in style, metamorphic grade, and intensity throughout a region, relationship to faults, shears, structures and mineral assemblages. 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.
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