Slate tends to break into flat sheets. This is illustrated in Figure 7.6, where the parent rock is shale, with bedding as shown. Chapter 22: A Classification of Metamorphic Rocks. Metamorphic rocks are an important topic in geology. 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. Classification of Metamorphic Rocks: 1. Knowing the parent rock helps us classify these rocks, and we can further classify them by their texture. II - Origin, Texture, and Classification of Metamorphic Rocks - Teklewold Ayalew ©Encyclopedia of Life Support Systems (EOLSS) Some metamorphic rocks, particularly those buried to depths of several kilometers, contain numerous veins rich in quartz and feldspar. Next: 7.3 Plate Tectonics and Metamorphism, Creative Commons Attribution 4.0 International License. Schist; Slate; Gneiss; Hornfels; Marble; Mylonites and cataclastites; Other classes Diorite. Metamorphic rocks that form under either low-pressure conditions or just confining pressure do not become foliated. Classification – Metamorphic rocks Foliated Metamorphic Rocks (structural terms/names) Types of foliations a. Compositional layering on less than cm scale b. Chapter 22: A Classification of Metamorphic Rocks • Metamorphic rocks are classified on the basis of texture and composition (either mineralogical or chemical) • Unlike igneous rocks, which have been plagued by a proliferation of local and specific names, metamorphic rock … The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are slate, phyllite, schist, and gneiss (Figure 7.8). 50, no. Gemologist Discovers Rock That Looks Like Cookie Monster, Five Rare Blue Diamonds Discovered at Cullinan Mine, A 99-Million-Year-Old Millipede, Perfectly Preserved in Amber, Tourmaline kyanite, staurolite, garnet, andalusite, Micas, chlorites, talc, stilpnomelane, prehnite, The composition of any fluid phase present during metamorphism, and. The mica crystals are consistently parallel to one another. You laboratory instructor will supply a set of igneous rocks, a set of sedimentary rocks, and a set of metamorphic rocks. 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. Classification of metamorphic rocks depends on what is visible in the rock and its degree of metamorphism. Metamorphic rocks are classified on the basis of texture and composition (either mineralogical or chemical) Unlike igneous rocks, which have been plagued by a proliferation of local and specific names, metamorphic rock … Most gneiss has little or no mica because it forms at temperatures higher than those under which micas are stable. Rocks: Igneous, Metamorphic and Sedimentary Rocks hold the history of the earth and the materials that will be used to build its future. However, the classifiction of metamorphic rocks is more difficult to get into than with igneous … This large boulder has bedding still visible as dark and light bands sloping steeply down to the right. Squeezing and heating alone (as shown in Figure 7.5) and squeezing, heating, and formation of new minerals (as shown in Figure 7.6) can contribute to foliation, but most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress (Figure 7.6). Igneous. Classification of Metamorphic Rocks. Preferred orientation of platy minerals c. Shape of deformed grains dG i i itid. Pegmatite. Select a rock, and take the appropriate path below to classify the rock. 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. Metamorphic rocks are classified on the basis of mineralogy and texture. Diabase. In most cases, this is because they are not buried deeply, and the heat for the metamorphism comes from a body of magma that has moved into the upper part of the crust. The texture can be foliated or nonfoliated. Using a new analysis technique, scien... Credit : Nathan Almeyda Aura quartz is quartz that has been enhanced with a combination of titanium and niobium. Metamorphic rocks-formation,classification, type, distribution Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. The bulk chemical composition of the rock. Geological classification 2. Quartzite is metamorphosed sandstone (Figure 7.11). TEXTURES Textures of metamorphic rocks fall into two broad groups, FOLIATED and NON-FOLIATED. 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). Foliated Metamorphic Rocks 2. Dead ringer for Cookie Monster? 10.3 Classification of Metamorphic Rocks Metamorphic rocks are broadly classified as foliated or non-foliated. Slate, for example, is characterized by aligned flakes of mica that are too small to see. Distribution of metamorphic rocks; Classification of metamorphic rocks. This effect is especially strong if the new minerals are platy like mica or elongated like amphibole. Figure 7.7 shows an example of this effect. Non-foliated rocks form when pressure is uniform, or near the surface where pressure is very low. It is dominated by quartz, and in many cases, the original quartz grains of the sandstone are welded together with additional silica. Three kinds of criteria are normally employed. Each of these will be discussed in turn, then we will summarize how metamorphic rocks are classified. This contributes to the formation of foliation. In some cases, hornfels has visible crystals of minerals like biotite or andalusite. Classification of metamorphic rocks is based on mineral assemblage, texture, protolith, and bulk chemical composition of the rock. Metamorphic rocks may be classified on the basis of foliation into two types. Schist and gneiss can be named on the basis of important minerals that are present. Physical classification 3. A very hard rock with a granular appearance and a glassy lustre. 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. In this article of Geomorphology(Geography UPSC), we will discuss the Classification of Rocks: Igneous, Sedimentary, and Metamorphic Rocks & Rock Cycle.ROCK SYSTEM. Chemically Formed Sedimentary Rocks 3. A schist consisting mostly of talc would be called a talc-magnesian schist. of its formation. These parent rocks can be any type of rock, meaning they can be igneous, sedimentary or even other metamorphic rocks. Dacite. Rocks are classified based on three major factors as follows : 1. These are Foliated metamorphic rocks and Non-foliated metamorphic rocks. Classification of Metamorphic Rocks by Russell B. Travis Web pages adapted from Quarterly of the Colorado School of Mines, vol. The surfaces of the sheets have a sheen to them. Each of these will be discussed in turn, then we will summarize how metamorphic rocks are classified. Non-foliated metamorphic rocks do not have aligned mineral crystals. Igneous Rocks: Photos, descriptions and facts about intrusive and extrusive igneous rocks. Note that classification is generally loose and practical such that names can be adapted to describe the rock in the most satisfactory way that conveys the important characteristics. Foliated metamorphic rocks are formed from direct exposure to pressure and heat. Organically Formed Sedimentary Rocks. Mineralogical - The most distinguishing minerals are used as a prefix to a textural term. Most commonly they belong to sedimentary and metamorphic groups of geological classification. Textural Classification of Metamorphic Rocks: Since metamorphic rocks can be formed from any type of existing rocks, their mineral composition ranges more widely than that of all other types of rock. If you continue browsing the site, you agree to the use of cookies on this website. Metamorphic facies The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are: slate, phyllite, schist, and gneiss (Figure 7.2. A schist containing porphyroblasts of K-feldspar would be called a K-spar porphyroblastic schist. Credit: Leif Moritz Amber from Age of the Dinosaurs Disc... A new discovery could be a clue for us to see if life could emerge elsewhere in the Solar System. If a rock is buried to a great depth and encounters temperatures that are close to its melting point, it will partially melt. It is composed primarily of hornblende (amphibole) and plagioclase, usually with very little 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. Classification of Metamorphic Rocks • Metamorphic rocks are classified on the basis of texture and composition (either mineralogical or chemical) • Unlike igneous rocks, which have been plagued by a proliferation of local and specific names, metamorphic rock names are These rocks differ in – Texture – the degree to which something is rough or smooth, or soft or hard The Earth’s crust is made up of various types of rocks and the scientific study of rocks is called petrology.. Figure 7.7 shows an example of this effect. Now, they're not parents like your mom and dad, but they do come from parent rocks. Metamorphic rocks are classified by their mineral composition, the source rock, also known as a protolith, and the context (pressure, temperature, hydrological features, etc.) 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). The mineral crystals don’t have to be large to produce foliation. This large boulder has bedding still visible as dark and light bands sloping steeply down to the right. 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 the chart below notice how each of the first three rocks become the parent rock for the next. 2.1 Electrons, Protons, Neutrons, and Atoms, 4.5 Monitoring Volcanoes and Predicting Eruptions, 5.3 The Products of Weathering and Erosion, Chapter 6 Sediments and Sedimentary Rocks, 6.3 Depositional Environments and Sedimentary Basins, Chapter 7 Metamorphism and Metamorphic Rocks, 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, Chapter 21 Geological History of Western Canada, 21.2 Western Canada during the Precambrian, Chapter 22 The Origin of Earth and the Solar System, 22.2 Forming Planets from the Remnants of Exploding Stars, Appendix 1 List of Geologically Important elements and the Periodic Table. Those that are bounded by their own crystal faces are termed, The pressure and temperature reached during metamorphism. The grade of metamorphism is primarily controlled by temperature. When it forms, the calcite crystals tend to grow larger, and any sedimentary textures and fossils that might have been present are destroyed. This is contact metamorphism. Grain size variation e. Preferred orientation of platy minerals in matrix without preferred orientation f. There is no evidence of foliation. Foliated rocks can be ordered in terms of increasing metamorphism. A fine-grained rock that splits into wavy sheets. The quartz crystals show no alignment, but the micas are all aligned, indicating that there was directional pressure during regional metamorphism of this rock. Some rocks, such as granite, do not change much at the lower metamorphic grades because their minerals are still stable up to several hundred degrees. The newly described millipede (Burmanopetalum inexpectatum) seen in amber. 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. 1. In the example shown in Figure 7.8d, the dark bands are largely amphibole while the light-coloured bands are feldspar and quartz. 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. The specimen shown above is about two inches (five centimeters) across. Protolithic -  If a rock has undergone only slight metamorphism such that its original texture can still be observed then the rock is given a name based on its original name, with the prefix meta- applied. Marble is metamorphosed limestone. (Image: Petra Diamonds.) In gneiss, the minerals may have separated into bands of different colours. Metamorphic rock is classified by texture and composition. Chemical classification Basalt. Foliated Metamorphic Rocks. The rock has split from bedrock along this foliation plane, and you can see that other weaknesses are present in the same orientation. A gneiss containing hornblende, pyroxene, quartz, and feldspar would be called a hornblende-pyroxene gneiss. Best known examples of calcareous or carbonate rocks are … Home » Rocks. Mechanically Formed Sedimentary Rocks 2. Granite. Three kinds of criteria are normally employed. Most sandstone contains some clay minerals and may also include other minerals such as feldspar or fragments of rock, so most quartzite has some impurities with the quartz. They cannot be covered by a simple scheme of classification, but a simple textural classification … 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. 1. The rock has split from bedrock along this foliation plane, and you can see that other weaknesses are present in the same orientation. Andesite. For example a schist derived from basalt is typically rich in the mineral chlorite, so we call it chlorite schist. Thus, a schist containing biotite, garnet, quartz, and feldspar, would be called a biotite-garnet schist. Types of Metamorphic Rocks. Note that classification is generally loose and practical such that names can be adapted to describe the rock in the most satisfactory way that conveys the important characteristics. If the hornfels formed in a situation without directed pressure, then these minerals would be randomly orientated, not foliated as they would be if formed with directed pressure. 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. Did you know that metamorphic rocks have parents? Classification of metamorphic rocks. Foliated metamorphic rocks appeared banded or layered. It turns out that both texture and grain size are functions of the degree, or grade of metamorphism. Where slate is typically planar, phyllite can form in wavy layers. ADVERTISEMENTS: In this article we will discuss about the classification of sedimentary rocks on the basis of the nature of sediments:- 1. The resulting rock, which includes both metamorphosed and igneous material, is known as a migmatite (Figure 7.9). Foliated metamorphic rock. A rock that is dominated by aligned crystals of amphibole. In each of the sections, you will find brief descriptions of TEXTURES and MINERAL COMPOSITIONS, and a classification chart based on these characteristics. For example: metabasalt, metagraywacke, meta-andesite, metagranite. Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. Classification of Metamorphic Rocks. 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). Similarly, a gneiss that originated as basalt and is dominated by amphibole, is an amphibole gneiss or, more accurately, an amphibolite. In these types of rocks, the dominant component is a CARBONATE > 50%, generally of Calcium and also of Magnesium. For example a schist with a lot of quartz and feldspar and some garnet and muscovite would be called a garnet-muscovite quartzo-feldspathic schist. 1 UNESCO – EOLSS SAMPLE CHAPTERS GEOLOGY – Vol. Some examples of non-foliated metamorphic rocks are marble, quartzite, and hornfels. While metamorphic rocks can be formed in different ways, the resulting rocks can also be categorized based on the way in which minerals align in the newly formed rock. 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. Some form during mountain-building by forces of others from the heat of igneous intrusions in regional metamorphism others from the heat of igneous intrusions in contact metamorphism. Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. The metamorphic rocks which are produced by this process as known as dynamothermal metamorphic rocks, and are some of the most commonly formed. 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. These are the rocks that form by the effects of heat, pressure, and shear upon igneous and sedimentary rocks. Classification of metamorphic rocks is based on mineral assemblage, texture, protolith, and bulk chemical composition of the rock. These are: Chemical - If the general chemical composition can be determined from the mineral assemblage, then a chemical name can be employed. 6.2 Classification of Metamorphic Rocks There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are massive (not foliated) because they have formed in an environment without directed pressure or relatively near the surface with very little pressure at all. Foliation is produced in a rock by the parallel alignment of platy minerals (e.g., muscovite, biotite, chlorite), needle-like minerals (e.g., hornblende), or tabular minerals (e.g., feldspars). Classification of metamorphic rocks depends on what is visible in the rock and its degree of metamorphism. There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure at all. Obsidian. Classification Of Metamorphic Rocks . 7.2 Classification of Metamorphic Rocks There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure at all. Metamorphic rocks are largely grouped into foliated and non-foliated rocks. Metamorphic rocks are classified on the basis of foliation into the following types: 1. A rock with visible minerals of mica and with small crystals of andalusite. An example of this is shown in Figure 7.12. There are two main types of metamorphic rocks. Even if formed during regional metamorphism, quartzite does not tend to be foliated because quartz crystals don’t align with the directional pressure. The following are the examples of metamorphic rocks: Slate: Clay becomes slate after metamorphosis [Texture = Foliated] Marble: Limestone becomes marble after metamorphosis [Texture = … As already noted, the nature of the parent rock controls the types of metamorphic rocks that can form from it under differing metamorphic conditions. Gabbro. As with igneous and sedimentary rocks, metamorphic rocks are classified on the basis of texture(grain size, shape, orientation) and mineral composition. Classification of Metamorphic Rocks Metamorphic rocks are named primarily on the basis of their textures and grain size. 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