Foliations typically bend or curve into a shear, which provides the same information, if it is of a scale which can be observed. a. T. Metamorphism at ocean ridges is mainly (a) contact (b) dynamic (c) hydrothermal (d) regional. What are the two textures of metamorphic rocks. Houston, TX: Lunar and Planetary Institute Read full text, Physical Geology, First University of Saskatchewan Edition by Karla Panchuk is licensed under CC BY-NC-SA 4.0 Adaptation: Renumbering, Remixing, https://openpress.usask.ca/physicalgeology/. The pattern of aligned crystals that results is called foliation. [http://commons.wikimedia.org/wiki/ File:Migmatite_in_Geopark_on_Albertov.JPG] Phyllite is similar to slate, but has typically been heated to a higher temperature; the micas have grown larger and are visible as a sheen on the surface. The lines are small amounts of glassy material within the quartz, formed from almost instantaneous melting and resolidification when the crystal was hit by a shock wave. 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). Drag the appropriate labels to their respective targets. 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). Examples of nonfoliated rocks include: hornfels, marble, novaculite, quartzite, and skarn. Foliation is usually formed by the preferred orientation of minerals within a rock. The mineral crystals dont have to be large to produce foliation. When a rock is squeezed under directed pressure during metamorphism it is likely to be deformed, and this can result in a textural change such that the minerals are elongated in the direction perpendicular to the main stress (Figure 7.5). Usually, this represents the protolith chemistry, which forms distinct mineral assemblages. Under these conditions, higher grades of metamorphism can take place closer to surface than is the case in other areas. Slaty cleavage is composed of platy minerals that are too small to see. This effect is especially strong if the new minerals grow in platy or elongated shapes. In contrast, nonfoliated metamorphic rocks do not contain minerals that align during metamorphism and do not appear layered. Marble is metamorphosed limestone. Contrast the rock known commercially as Black Marinace Gold Granite (Figure 6.24)but which is in fact a metaconglomeratewith the metaconglomerate in Figure 6.10. It is composed of alternating bands of dark and light minerals. Platy minerals tend to dominate. Non-foliated metamorphic rocks do not have a layered or banded appearance. In this treatment, we'll describe metamorphic rock that does not show visible alignment of materials as massive. Foliated metamorphic rocks exhibit layers or stripes caused by the elongation and alignment of minerals in the rock as it undergoes metamorphism. Phyllite is a third type of foliated metamorphic rock. Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. Some examples of non-foliated metamorphic rocks are marble, quartzite, and hornfels. As a rock heats up, the minerals that melt at the lowest temperatures will melt first. The specimen shown above is about two inches (five centimeters) across. 2. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. 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. 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. Metamorphic rocks can be foliated, displaying banding or lamellar texture, or non-foliated. Want to create or adapt OER like this? These properties make it useful for a wide variety of architectural, practical, and artistic uses. Question 14. 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. University of Notre Dame: Prograde Metamorphism. For rocks at the surface, the true starting point for the rock cycle would be (a) igneous (b) sedimentary (c) metamorphic. Mariposite is a word that has been used in many ways. Novaculite is a dense, hard, fine-grained, siliceous rock that breaks with a conchoidal fracture. Essentials of Geology, 3rd Ed, Stephen Marshak. An example of contact metamorphism, where magma changes the type of rock over time, Metamorphism of slate, but under greater heat and pressure thane slate, Often derived from metamorphism of claystone or shale; metamorphosed under more heat and pressure than phyllite, Metamorphism of various different rocks. At an oceanic spreading ridge, recently formed oceanic crust of gabbro and basalt is slowly moving away from the plate boundary (Figure 6.26). The mica crystals are consistently parallel to one another. Weathering, Sediment, and Soil, Chapter 10. 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. Rocks that form from regional metamorphism are likely to be foliated because of the strong directional pressure of converging plates. Lapis Lazuli, the famous blue gem material, is actually a metamorphic rock. Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. Well foliated to nearly massive quartz monzonite gneiss, generally medium-grained and even textured but locally porphyritic and pegmatitic. The figure below shows a metaconglomerate. Slate exhibits slaty foliation, which is also called cleavage. Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. Metaconglomerate, however, breaks through the grains, as the cement has recrystallized and may be as durable as the clasts. Pressures in the lower mantle start at 24 GPa (GigaPascals), and climb to 136 GPa at the core-mantle boundary, so the impact is like plunging the rock deep into the mantle and releasing it again within seconds. Under extreme conditions of heat and pressure, Contact metamorphism of various different rock types. This is a megascopic version of what may occur around porphyroblasts. Marble is composed of calcite and will readily react to a small drop of HCl. [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. It is foliated, crenulated, and fine-grained with a sparkly appearance. NONFOLIATED METAMORPHIC ROCKS As opposed to the foliated metamorphic rocks, the nonfoliated rocks are not distinctly layered. Foliation, as it forms generally perpendicular to the direction of principal stress, records the direction of shortening. Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet. Foliated - those having directional layered aspect of showing an alignment of particles like gneiss. Metaconglomerate looks similar to conglomerate, although sometimes the clasts are deformed. The specimen shown above is about two inches (five centimeters) across. Names given to rocks that are sold as building materials, especially for countertops, may not reflect the actual rock type. - Examples: quartzite derived from the metamorphism of sandstone, and marble derived from the metamorphism of limestone or dolostone. It is dominated by quartz, and in many cases, the original quartz grains of the sandstone are welded together with additional silica. The metaconglomerate formed through burial metamorphism does not display any of the foliation that has developed in the metaconglomerate in Figure 6.10. Some types of metamorphism are characteristic of specific plate tectonic settings, but others are not. Springer. Image copyright iStockPhoto / RobertKacpura. Most gneiss has little or no mica because it forms at temperatures higher than those under which micas are stable. This happens because the stress can cause some parts of the quartz crystals to dissolve, and the resulting ions flow away at right angles to the greatest stress before forming crystals again. Schistose foliation is composed of larger minerals which are visible to the unaided eye. Anthracite is the highest rank of coal. 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. Introduction to Hydrology and Groundwater, 12a. Measurement of the intersection between a fold's axial plane and a surface on the fold will provide the fold plunge. The aligned minerals are mostly mica, which has a platy crystal habit, with plates stacked together like pages in a book. It is often referred to as "hard coal"; however, this is a layman's term and has little to do with the hardness of the rock. A rock with visible minerals of mica and with small crystals of andalusite. Protoliths are transformed chemically and physically by high temperatures, high pressures, hot fluids or some combination of these conditions. This is related to the axis of folds, which generally form an axial-planar foliation within their axial regions. It is composed primarily of quartz. When a rock is both heated and squeezed during metamorphism, and the temperature change is enough for new minerals to form from existing ones, there is a likelihood that the new minerals will be forced to grow with their long axes perpendicular to the direction of squeezing. The metaconglomerate formed through burial metamorphism does not display any of the foliation that has developed in the metaconglomerate in Figure 10.10. With aligned minerals that are coarse enough to see, rocks that exhibit schistose foliation sparkle, because they contain micas that reflect light. The outcome of metamorphism depends on pressure, temperature, and the abundance of fluid involved, and there are many settings with unique combinations of these factors. 1. The Geology.com store offers inexpensive rock collections that can be mailed anywhere in the United States or U.S. Texture is divided into two groups. Most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress. French, B.M. This is probably because nonfoliated rocks were exposed to high temperature conditions, but not to high directional pressure conditions. In some cases, hornfels has visible crystals of minerals like biotite or andalusite. A hard rock that is easy to carve, marble is often used to make floor tiles, columns and sculptures. The figure below shows a metaconglomerate. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix of sand, silt, or clay. is another name for thermal metamorphism. What are some of the differences between foliated rocks and nonfoliated rocks? The collisions result in the formation of long mountain ranges, like those along the western coast of North America. In the example shown in Figure 7.8d, the dark bands are largely amphibole while the light-coloured bands are feldspar and quartz. Usually, this is the result of some physical force and its effect on the growth of minerals. The larger size gives the foliation a slighly shiny appearance. Shale, slate, phyllite, schist, gneiss, partial melting Match each rock with its first-order metamorphic equivalent (the first rock it would turn into when metamorphosed). Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks. Often, retrograde metamorphism will not form a foliation because the unroofing of a metamorphic belt is not accompanied by significant compressive stress. In contrast, nonfoliated metamorphic rocks do not contain minerals that align during metamorphism and do not appear layered. . One kind of foliation is called gneissic banding, which looks like bands of light and dark layers. If a rock is both heated and squeezed during metamorphism, and the temperature change is enough for new minerals to form from existing ones, the new minerals can be forced to grow longer perpendicular to the direction of squeezing (Figure 10.7). Slate, for example, is characterized by aligned flakes of mica that are too small to see. . Foliation may parallel original sedimentary bedding, but more often is oriented at some angle to it. It often contains significant amounts of mica which allow the rock to split into thin pieces. This is not always the case, however. These are the result of quartz . Phyllitic foliation is composed of platy minerals that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided eye. Adding foil creates a layer, so foliated rocks are layered rocks. Metamorphic rocks that form under either low-pressure conditions or just confining pressure do not become foliated. Foliated textures show four types of foliation. Click on image to see enlarged photo. Contact metamorphic aureoles are typically quite small, from just a few centimeters around small dykes and sills, to as much as 100 m around a large stock. One derived from shale may be a muscovite-biotite schist, or just a mica schist, or if there are garnets present it might be mica-garnet schist. 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 best way to learn about rocks is to have a collection of specimens to examine while you study. Introduction to Hydrology and Shorelines, 14a. . Dynamic metamorphism is the result of very high shear stress, such as occurs along fault zones. The layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Most of the blueschist that forms in subduction zones continues to be subducted. It is a rock of intermediate metamorphic grade between phyllite and gneiss. 2.1 Electrons, Protons, Neutrons, and Atoms, 4.5 Monitoring Volcanoes and Predicting Eruptions, 5.3 The Products of Weathering and Erosion, 6.3 Depositional Environments and Sedimentary Basins, 7.5 Contact Metamorphism and Hydrothermal Processes, 9.1 Understanding Earth through Seismology, 10.1 Alfred Wegener the Father of Plate Tectonics, 10.2 Global Geological Models of the Early 20th Century, 10.3 Geological Renaissance of the Mid-20th Century, 10.4 Plates, Plate Motions, and Plate-Boundary Processes, 11.5 Forecasting Earthquakes and Minimizing Damage and Casualties, 15.1 Factors That Control Slope Stability, 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting, 21.2 Western Canada during the Precambrian, Chapter 22 The Origin of Earth and the Solar System, Karla Panchuk, Department of Geological Sciences, University of Saskatchewan, 22.2 Forming Planets from the Remnants of Exploding Stars, Appendix 1 List of Geologically Important elements and the Periodic Table, Chapter 7 Metamorphism and Metamorphic Rocks.