Typically this will be initially described as foliated or non foliated. Furthermore, the texture of sedimentary rocks affects such derived properties of these rocks as porosity, permeability, bulk density, electrical conductivity, and sound transmissibility. This chapter describes different types of textures … Foliation is described as the existence or appearance of layers. The texture of a metamorphic rock is both a description of its constituent minerals along with their arrangement and size. For example : Biotite schist, hornblende schist, chlorite-granet schist, kyanite schist, etc. This type of metamorphic was created by regional metamorphism, in which a sedimentary or igneous rock has been deeply buried and subjected to high temperatures and pressures. All images have two views, in plane- and cross-polarized light. New minerals form that are in equilibrium with the new environment, and a new rock texture develops in response to the growth of new minerals. • Processes leading to texture formation • Textures of Contact Metamorphism • High Strain Metamorphic Textures • Regional Metamorphic Textures • Replacement Textures and Reaction Rims 2. A change in the texture, structure, or chemical composition of a rock due to contact with magma Shape of mineral grains: rounded, angular, or elongated. Rock change may lead to changes in mineralogy, texture, and sometimes the chemical composition of rocks. These can range from textures similar to the original protolith at low grades of metamorphism, to textures that are purely produced during metamorphism and leave the rock with little resemblance to the original protolith. Phaneritic textures are where interlocking crystals of igneous rock are visible to the unaided eye. Allothimorph —a constituent of a metamorphic rock that has not changed its original crystal outline. Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) 1 Olivine: forsterite Olivine: Forsterite, in marble. Here we examine only the foliated types. Metamorphic textures are divided into two categories: foliated and non-foliated. It is popular for a wide variety of uses such as roofing, flooring, and flagging because of its durability and attractive appearance. Rocks which exhibit foliation are said to exhibit a planar texture. The most important non-foliated rock is marble. Classification of metamorphic rocks is based on mineral assemblage, texture, protolith, and bulk chemical composition of the rock. [2] Porphyritic texture is one in which larger pieces ( phenocrysts ) are embedded in a background mass made of much finer grains. Metamorphic Rocks: Metamorphic rocks are made through the process of intense heat and pressure that is applied to a sedimentary, metamorphic, or igneous rock. If a rock is foliated, its name is determined by the type of foliation present and the dominant minerals—for example, a kyanite schist. Foliated metamorphic rocks. Metamorphic rocks exhibit a variety of textures. Some rocks may even appear to be non-foliated and banded. The formation of granoblastic textures occurs to minimise the combined surface energy of phases within a rock. Foliation - any planar set of minerals, or banding of mineral concentrations, especially the planar structure that results from flattening of the mineral grains, like micas. Slate is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. There are nine main types of igneous rock textures: Phaneritic, vesicular, aphanitic, porphyritic, poikilitic, glassy, pyroclastic, equigranular, and spinifex. Strong foliation in fine-grained metamorphic rocks. Like igneous rocks, metamorphic rocks are classified based on texture and composition. The changes that occur during metamorphism may involve changes in rock texture, in the minerals present, and sometimes in overall rock composition. There are fundamental types of metamorphism: regional metamorphism and phone, or thermal, metamorphism. 8.3 Regional metamorphism is more intense at depth Metamorphic Textures. Each kind of texture has a variety of different characteristics that make them unique. If the minerals are segregated into alternating light‐colored and dark‐colored layers, the rock is called a gneiss. Metamorphic Textures provides definitions, descriptions and illustrations of metamorphic textures, as well as the fundamental processes involved in textural development.This book is composed of 11 chapters and begins with a presentation of the metamorphic processes and the production of metamorphic minerals. Metamorphic rocks are categorised by way of texture and mineralogy. Metamorphic rock can also be formed from tectonic processes such as continental collisions. The process where one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure Define contact metamorphism. Metamorphic rock, any rock that results from the alteration of preexisting rocks in response to changing conditions, such as variations in temperature, pressure, and mechanical stress, and the addition or subtraction of chemical components. The following are textures, or terms used in relation to textures, of metamorphic rocks; * indicates an illustration in the cross-reference. Most Metamorphic rocks form in the influence of a directed stress field. Arrangement of mineral grains: aligned or un-aligned (massive or homogeneous). Metamorphic rocks are eventually exposed at the surface by uplift and erosion of the overlying rock. Foliation can occur in both igneous and metamorphic rocks (this section will only focus on foliation in metamorphic rocks). 6.2 Metamorphic textures . Foliation in metamorphic rocks occurs when the … The pressure applied to the reforming rock causes the differences in the way the rock looks once recrystallized and determines whether it will be foliated or nonfoliated. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. Metamorphic Rocks. This is a somewhat haphazard collection of metamorphic textures and rocks seen in thin section, with some discussion of the processes thought to have made them. Planar texture can … Granoblastic texture: is an equigranular texture in which crystals adopt a polygonal morphology with grain triple junctions of approximately 120 degrees. The preexisting rocks may be igneous, sedimentary, or other metamorphic rocks. Types: Igneous rocks are of two types – intrusive (solidified from magma below the earth’s surface) and extrusive (solidified from lava on the surface of the earth) Metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (), without the protolith melting into liquid magma (a solid-state change). … Metamorphic rocks form by recrystallization in the solid state because of changes in temperature, pressure, or the composition of pore fluids. Most of metamorphic rocks have good crystallization, compact textures, high strength, small porosity, and low water permeability. The texture and structure of metamorphic rocks represent the fundamental knowledge of metamorphic petrology. Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. The texture of a metamorphic rock can be either foliated and appear layered or banded, or non-foliated and appear uniform in texture without banding. Metamorphic petrologists study metamorphic rocks to interpret those histories. Metamorphic rocks are classified by texture and by mineral composition. It is composed primarily of the mineral calcite (CaCO 3 ) and usually contains other minerals, such as clay minerals, micas, quartz , pyrite , iron oxides, and graphite . Textures and Structures of Metamorphic Rocks 1. Over time, this collection should become more orderly and comprehensive, but don't hold your breath. Along with other properties of these rocks, it helps to characterize and distinguish them from other types of rocks and it aids in their correlation. Most classifications of metamorphic rocks involve first separating the rocks into two categories by their texture -foliated rocks and non-foliated rocks. Granoblastic texture is the typical equigranular texture formed in metamorphic rocks when grains mutually adjust their boundaries in the solid state in an attempt to achieve textural equilibrium. Foliated texture is where metamorphic rock is made of layers of materials. The subsequent chapters describe the structural classification of grain … Some examples of metamorphic rocks are gneiss, slate, marble, schist, quartzite, hornblende, and phyllite. The major differences between foliated and nonfoliated metamorphic rocks are in the areas of texture, appearance and the type of pressure applied during recrystallization. Foliated Textures. Metamorphic rock textures are foliated, non-foliated, or lineated are described below.. Metamorphic rock identification table. It is a characteristic of foliation planes, and the rocks showing this texture are found under greenschist, amphibolite, and eclogite metamorphic facies. Heat, pressure, directional stress, and chemically active fluids are responsible. Engineering Uses of Metamorphic Rocks: The metamorphic rocks are extensively used as building stones. Gneiss ("nice") is a rock of great variety with large mineral grains arranged in wide bands. Textural features of metamorphic rocks have been discussed in the previous lecture. The foliated rocks like slate, gneiss and schist are used as roofing material tabletops, staircases, etc. Each of these will be discussed in turn, then we will summarize how metamorphic rocks are classified. Metamorphic rock - Metamorphic rock - Classification of metamorphic rocks: Because of the diverse chemistry, mineralogy, and primary origin of metamorphic rocks and because of the diverse fabrics or textures that may develop depending on the stresses that may operate during their formation, there is no simple, universally used classification of these rocks. The texture of metamorphic rocks is foliated due to pressure. A rock’s texture is a description of: Size of mineral grains: fine, medium, or coarse. The foliation or layering that occurs in these rocks is because of the immense directional pressure they undergo deep within the Earth, usually along the boundary of a converging tectonic plate. Plane-polarised light, width of view 2.5 mm. Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. Texture In metamorphic rocks individual minerals may or may not be bounded by crystal faces. 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