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) … Metamorphic Rocks: Metamorphic rocks are made through the process of intense heat and pressure that is applied to a sedimentary, metamorphic, or igneous rock. 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. Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) 1 Olivine: forsterite Olivine: Forsterite, in marble. Metamorphic rocks form by recrystallization in the solid state because of changes in temperature, pressure, or the composition of pore fluids. Metamorphic Textures. Phaneritic textures are where interlocking crystals of igneous rock are visible to the unaided eye. Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. [2] Porphyritic texture is one in which larger pieces ( phenocrysts ) are embedded in a background mass made of much finer grains. 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. The most important non-foliated rock is marble. Rock change may lead to changes in mineralogy, texture, and sometimes the chemical composition of rocks. The following are textures, or terms used in relation to textures, of metamorphic rocks; * indicates an illustration in the cross-reference. Metamorphic rocks exhibit a variety of textures. Foliated Textures. Most classifications of metamorphic rocks involve first separating the rocks into two categories by their texture -foliated rocks and non-foliated rocks. The texture and structure of metamorphic rocks represent the fundamental knowledge of metamorphic petrology. If the minerals are segregated into alternating light‐colored and dark‐colored layers, the rock is called a gneiss. It means a type of rock texture, not a composition. Metamorphic Rocks. Foliated Rock Textures Foliation is broadly defined as any planar arrangement of mineral grains or structural features in a rock. Typically this will be initially described as foliated or non foliated. A rock’s texture is a description of: Size of mineral grains: fine, medium, or coarse. Over time, this collection should become more orderly and comprehensive, but don't hold your breath. Metamorphic rocks are categorised by way of texture and mineralogy. 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. Texture In metamorphic rocks individual minerals may or may not be bounded by crystal faces. Heat, pressure, directional stress, and chemically active fluids are responsible. Shape of mineral grains: rounded, angular, or elongated. The changes that occur during metamorphism may involve changes in rock texture, in the minerals present, and sometimes in overall rock composition. All images have two views, in plane- and cross-polarized light. 8.3 Regional metamorphism is more intense at depth 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. Gneiss ("nice") is a rock of great variety with large mineral grains arranged in wide bands. Metamorphic rocks are eventually exposed at the surface by uplift and erosion of the overlying rock. Strong foliation in fine-grained metamorphic rocks. • Processes leading to texture formation • Textures of Contact Metamorphism • High Strain Metamorphic Textures • Regional Metamorphic Textures • Replacement Textures and Reaction Rims 2. Slate is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. The process where one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure Define contact metamorphism. Classification of metamorphic rocks is based on mineral assemblage, texture, protolith, and bulk chemical composition of the rock. 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. Foliation can occur in both igneous and metamorphic rocks (this section will only focus on foliation in metamorphic rocks). If a rock is foliated, its name is determined by the type of foliation present and the dominant minerals—for example, a kyanite schist. A change in the texture, structure, or chemical composition of a rock due to contact with magma 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. Allothimorph —a constituent of a metamorphic rock that has not changed its original crystal outline. Furthermore, the texture of sedimentary rocks affects such derived properties of these rocks as porosity, permeability, bulk density, electrical conductivity, and sound transmissibility. Metamorphic textures are divided into two categories: foliated and non-foliated. There are fundamental types of metamorphism: regional metamorphism and phone, or thermal, metamorphism. It is popular for a wide variety of uses such as roofing, flooring, and flagging because of its durability and attractive appearance. Like igneous rocks, metamorphic rocks are classified based on texture and composition. The preexisting rocks may be igneous, sedimentary, or other metamorphic rocks. The formation of granoblastic textures occurs to minimise the combined surface energy of phases within a rock. Metamorphic rocks are classified by texture and by mineral composition. The texture of a metamorphic rock is both a description of its constituent minerals along with their arrangement and size. The texture of metamorphic rocks is foliated due to pressure. 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. 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. Foliation in metamorphic rocks occurs when the … It is a characteristic of foliation planes, and the rocks showing this texture are found under greenschist, amphibolite, and eclogite metamorphic facies. Some rocks may even appear to be non-foliated and banded. The foliated rocks like slate, gneiss and schist are used as roofing material tabletops, staircases, etc. These changes record geologic processes and events of the past. Here we examine only the foliated types. Rocks which exhibit foliation are said to exhibit a planar texture. Each kind of texture has a variety of different characteristics that make them unique. Metamorphic rock can also be formed from tectonic processes such as continental collisions. 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. 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). Granoblastic texture: is an equigranular texture in which crystals adopt a polygonal morphology with grain triple junctions of approximately 120 degrees. There are two basic types of texture for a metamorphic rock. Engineering Uses of Metamorphic Rocks: The metamorphic rocks are extensively used as building stones. Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. Metamorphic petrologists study metamorphic rocks to interpret those histories. There are nine main types of igneous rock textures: Phaneritic, vesicular, aphanitic, porphyritic, poikilitic, glassy, pyroclastic, equigranular, and spinifex. Some examples of metamorphic rocks are gneiss, slate, marble, schist, quartzite, hornblende, and phyllite. This chapter describes different types of textures … Most of metamorphic rocks have good crystallization, compact textures, high strength, small porosity, and low water permeability. Each of these will be discussed in turn, then we will summarize how metamorphic rocks are classified. Foliated metamorphic rocks. The subsequent chapters describe the structural classification of grain … Planar texture can … 6.2 Metamorphic textures . Foliation is described as the existence or appearance of layers. For example : Biotite schist, hornblende schist, chlorite-granet schist, kyanite schist, etc. Textures and Structures of Metamorphic Rocks 1. Most Metamorphic rocks form in the influence of a directed stress field. Metamorphic rock textures are foliated, non-foliated, or lineated are described below.. Metamorphic rock identification table. Plane-polarised light, width of view 2.5 mm. Textural features of metamorphic rocks have been discussed in the previous lecture. 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 . 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 textures are either granular or foliated. Foliated texture is where metamorphic rock is made of layers of materials. 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 major differences between foliated and nonfoliated metamorphic rocks are in the areas of texture, appearance and the type of pressure applied during recrystallization. Arrangement of mineral grains: aligned or un-aligned (massive or homogeneous). 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. 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. 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