Metamorphism and Metamorphic Rocks, Chapter 13. Differential stress has caused quartz pebbles within the rock to become elongated, and it has also caused wings to form around some of the pebbles (see the pebble in the dashed ellipse). The larger size gives the foliation a slighly shiny appearance. Some types of metamorphism are characteristic of specific plate tectonic settings, but others are not. It has a bright, lustrous appearance and breaks with a semi-conchoidal fracture. The planar fabric of a foliation typically forms at right angles to the maximum principal stress direction. The specimen shown above is about two inches (five centimeters) across. It is composed primarily of quartz. Question 14. Even if formed during regional metamorphism, quartzite does not tend to be foliated because quartz crystals dont align with the directional pressure. is another name for dynamothermal metamorphism. A large intrusion will contain more thermal energy and will cool much more slowly than a small one, and therefore will provide a longer time and more heat for metamorphism. It is composed primarily of hornblende (amphibole) and plagioclase, usually with very little quartz. Soapstone is a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes, and carbonates. 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. Crenulation cleavage and oblique foliation are particular types of foliation. Foliations, in a regional sense, will tend to curve around rigid, incompressible bodies such as granite. 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. Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. Slate tends to break into flat sheets. Further identification of non-foliated rocks is dependent on the composition of the minerals or components in the rock. Non-foiliated - those having homogeneous or massive texture like marble. (PDF) Petrostructural Features of Metaconglomerate in Igarra and Otuo, South-Western Nigeria Petrostructural Features of Metaconglomerate in Igarra and Otuo, South-Western Nigeria Authors:. 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. 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. The best way to learn about rocks is to have a collection of specimens to examine while you study. 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. https://en.wikipedia.org/w/index.php?title=Foliation_(geology)&oldid=1134898332, the mineralogy of the folia; this can provide information on the conditions of formation, whether it is planar, undulose, vague or well developed, its orientation in space, as strike and dip, or dip and dip direction, its relationship to other foliations, to bedding and any folding. The pebbles in this sample are not aligned and elongated as in the metaconglomerate in Figure 10.10. mineral cleavage. 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. In gneiss, the minerals may have separated into bands of different colours. French, B.M. Some examples of. The tendency of slate to break into flat pieces is called slaty cleavage. This effect is especially strong if the new minerals grow in platy or elongated shapes. Molecular Biology and Genetics. Platy minerals tend to dominate. 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. It is produced by contact metamorphism. Chlorite and serpentine are both hydrated minerals, containing water in the form of OH in their crystal structures. The specimen shown above is about two inches (five centimeters) across. Rockman's metamorphic rock specimens are hand broken as opposed to being crushed which helps keep cleavage and fracture characteristics intact. 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. Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Foliation Glaucophane is blue, and the major component of a rock known as blueschist. Alignment of tabular minerals in metamorphic rocks, igneous rocks and intrusive rocks may form a foliation. It is foliated, crenulated, and fine-grained with a sparkly appearance. In geotechnical engineering a foliation plane may form a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) Supplying quality educational materials for teachers, collectors and other educational organizations since 1995. If stress from all directions is equal, place all thin arrows. The protolith for a schist is usually shale, a type of sedimentary rock. It is composed primarily of calcium carbonate. 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). 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. of rock masses in, for example, tunnel, foundation, or slope construction. Schist is a metamorphic rock with well-developed foliation. It forms from sediments deposited in marine environments where organisms such as diatoms (single-celled algae that secrete a hard shell composed of silicon dioxide) are abundant in the water. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. What are some of the differences between foliated rocks and nonfoliated rocks? 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. Minerals are homogeneous, naturally occurring inorganic solids. The cement matrix of conglomerate is not as durable as the grains, and hence when broken, conglomerate breaks around the grains. However, compositional banding can be the result of nucleation processes which cause chemical and mineralogical differentiation into bands. 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. The aligned minerals are mostly mica, which has a platy crystal habit, with plates stacked together like pages in a book. 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. Weakly foliated: Any material: Hard, fine-grained rock: Metaconglomerate: Weakly foliated: Quartz-rich conglomerate: Strongly stretched pebbles: Amphibolite: Weakly foliated: Mafic volcanic rocks: Coarse-grained: Examples of metamorphic rock: Index Reference Lutgens and Tarbuck Ch 7 . 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). c. hydrothermal. 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). The mica crystals are consistently parallel to one another. 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). Dynamic metamorphism is the result of very high shear stress, such as occurs along fault zones. An example of a synthetic material is the one referred to as quartz, which includes ground-up quartz crystals as well as resin. 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 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. 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/. If a foliation does not match the observed plunge of a fold, it is likely associated with a different deformation event. Names given to rocks that are sold as building materials, especially for countertops, may not reflect the actual rock type. Protoliths are transformed chemically and physically by high temperatures, high pressures, hot fluids or some combination of these conditions. A second type of nonfoliated metamorphic rock, quartzite, is composed mostly of silicon dioxide. Polymict metaconglomeraat, . The specimen shown above is about two inches (five centimeters) across. Foliated metamorphic rocks have elongated crystals that are oriented in a preferred direction. Skarn is a rock characterized by its formation rather than its mineral composition. A fine-grained rock that splits into wavy sheets. 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. This planar character can be flat like a piece of slate or folded. Often this foliation is associated with diagenetic metamorphism and low-grade burial metamorphism. In gneiss, the foliation is more typically represented by compositional banding due to segregation of mineral phases. Some examples of foliated rocks include. One kind of foliation is called gneissic banding, which looks like bands of light and dark layers. Foliated - those having directional layered aspect of showing an alignment of particles like gneiss. 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. Determination of this information is not easily accomplished in this lab. (1998). Most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress. This typically follows the same principle as mica growth, perpendicular to the principal stress. 30 seconds. In the example shown in Figure 7.8d, the dark bands are largely amphibole while the light-coloured bands are feldspar and quartz. VALLEY, John W.1, CAVOSIE, A.J., WILDE, S.A., GRANT, M., and LIU, Dunyi, http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_39602.htm, ftp://rock.geosociety.org/pub/reposit/2002/2002034.pdf, https://en.wikipedia.org/w/index.php?title=Metaconglomerate&oldid=1007375955, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 17 February 2021, at 20:28. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. This is related to the axis of folds, which generally form an axial-planar foliation within their axial regions.
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