texture and structure of metamorphic rocks

The words "texture" and "microstructure" are interchangeable, with the latter preferred in modern geological literature. Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". Figure 7.1 Metamorphic rock (gneiss) of the Okanagan Metamorphic and Igneous Complex at Skaha Lake, B.C. This is a porphyritic basalt that was regionally metamorphosed to epidote amphibolite facies. Metamorphic rock textures are foliated, non-foliated, or lineated are described below. porphyroblastic. These rocks get their name from the Latin word sedimentum which means settle down. Rock microstructure includes the texture of a rock and the small scale rock structures. Textures. You can either follow the sequence through in order, or else scroll down the list below (which roughly follows the outline of lecture 3) and click on individual terms. The original rock (called the “protolith”) is either an igneous or sedimentary rock. Metamorphic rocks were once igneous or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth’s crust. Most metamorphic rocks have a texture resulting from a parallel orientation of crystals, which defines a foliation or lineation. Earth Sciences 2: Introduction to Metamorphic Rocks. Grain shapes 2. Metamorphic rock textures are foliated, non-foliated, or lineated are described below. If a rock is foliated, its name is determined by the type of foliation present and the dominant minerals—for example, a kyanite schist. source. Metamorphic rocks are classified as either foliated or non foliated depending on their mineral structure and pattern; Metamorphic rocks are rocks that have changed from one type of rock to another. aphanitic. Grain distributions 5. Other factors include the diffusion rate, which is how atoms and molecules move through the liquid. burial, regional metamorphic rocks) – Slaty cleavage – Phyllitic – Schistose – Gneissose – Mylonitic • Non Foliation; equidimentional rock fabric (e.g. Foliated metamorphic rocks. First, is the fact that metamorphism takes place through heat, pressure, and chemically … It is one of the features that helps differentiate gneiss from other foliated rocks. Metamorphic Fabric and Texture FABRIC: Refers to orientation of the crystallographic lattices of the minerals TEXTURE: Refers to mineral distributions or orientations within the rock, overall structure of the rock. When it forms, the calcite crystals tend to grow larger, and any sedimentary textures and fossils that might have been present are destroyed. However, the classifiction of metamorphic rocks is more difficult to get into than with igneous and sedimentary rocks, for a couple of reasons. (i) Slaty structure: The slaty structure is also called slaty cleavage. The changed rock is called the metamorphic rock and it will be stable under the new set of conditions till there is a further change in those conditions. cryptocrystalline. Metamorphic rocks exhibit a variety of textures. Allothimorph —a constituent of a metamorphic rock that has not changed its original crystal outline. (Source: Belinda Madsen) 6.2.1: Foliation and Lineation. Metamorphic rock is classified by texture and composition. These are a few examples of igneous feature that survived regional-scale deformation. Cleavage Planar Fabric of Preferred Fracture, sub-parallel orientation, non-penetrative. Schistose. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Such features include folds, nappes, and faults with a wide variety of geometries. Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. This is a set of photomicrographs illustrating metamorphic textures, arranged as a slide show. The nomenclature of metamorphic rocks is classified according to various criteria, especially texture, composition, and P–T conditions of metamorphism. While sedimentary rock is formed from sediments, and igneous rock is formed from molten magma, metamorphic rock is rock made from pre-existing rocks. It all comes down to the rate at which the rock cools. Foliated metamorphic rocks appeared banded or layered. Sedimentary Rocks. Examples of metamorphic rocks whose normal structure … The foliated rock types that form under these conditions are called schist or gneiss, depending on their texture. 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. If the minerals are segregated into alternating light‐colored and dark‐colored layers, the rock is called a gneiss. Throughout their cooling history all magmatic rocks try to achieve mechanical and chemical equilibrium, but rarely succeed. Foliation is a term used that describes minerals lined up in planes. PLAY. Allotrioblast(ic) —see Xenoblast(ic) Atoll —see * Atoll garnet. The original rock is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (100 megapascals (1,000 bar) or more), causing profound physical or chemical change.The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rock identification table. The following are textures, or terms used in relation to textures, of metamorphic rocks; * indicates an illustration in the cross-reference. Relict igneous textures in metamorphic rocks are relatively common, mostly requiring that deformation has been limited enough to allow them to survive. Metamorphic rocks are the third great class of rocks. The texture of sedimentary rocks depends on their clast, age, and depositional setting. Metamorphic rock identification table. Metamorphic rocks are the product of “metamorphism”, which is the partial or complete recrystallization of rocks. Non-foliated rocks occur when heat is high, but pressure is low or equal on all sides. grains visible with the unaided eye. The structures of the metamorphic rocks are: (i) Slaty structure, (ii) Schistose structure, (iii) Gneissose structure, and (iv) Granulose structure. METAMORHISM is the term used to express the process responsible for all the changes that take place in an original rock under the influence of changes in the surrounding conditions of temperature, pressure and chemically active fluids. Metamorphic rock - Metamorphic rock - Structural features: Metamorphic rocks are often intimately related to large-scale (kilometres of tens of kilometres) structural features of Earth. The texture can be foliated or nonfoliated. Start studying Lab 5 - Textures and Structures of Rocks II. The texture of a rock provides a clue whether the magma cooled fast or slowly and where the rock was formed. Metamorphic. Grain orientations 4. If the transformation is incomplete we can observe a serpentine mesh structure composed of a lattice work of longitudinally divided cross-fibre veins enclosing olivine cores. Textural features of metamorphic rocks have been discussed in the previous lecture. Metamorphic rock Texture and Structure of Metamorphic Rocks Texture Grain size from EASC 1402 at The University of Hong Kong Rock cycle means the process by which rocks are formed, degraded and reformed by the internal geological processes like plutonism, volcanism, uplift etc and/or by external geological process like erosion, weathering, … Metamorphic Structures and Textures • Structure – features that characterize handspecimen or larger masses of rock. Structure and Texture Anastasia Neni Metamorphic structure • Foliation; planar rock fabric (e.g. microcrystalline . phaneritic. STUDY. They have a very fine grained structure. These are generally grainy. They are crystalline and often have a “squashed” (foliated or banded) texture. Foliation is a term used that describes minerals lined up in planes. What determines igneous rock texture? These rocks undergo a change, … Mineralogically, tends to include quartz, feldspar, mica, chlorite, and other clay minerals. Others have a more isotropic arrangement of mineral grains. Sediments are the smaller particles / fragments that are formed by the breaking … Metamorphism. Like water cycle, there exist rock cycle (geological cycle) in geology. Metamorphic Microstructures. The Deccan Plateau is made up of basalt rocks. The texture of a metamorphic rock is a unique product of its mineralogy and metamorphic conditions. The rock possessing slaty cleavage has a unique property of splitting into thin sheets. Slate. Foliated metamorphic rock. Metamorphic rocks are rocks whose structure and appearance have been affected or changed by greater heat, pressure and chemical processes, usually while buried deep below the Earth’s surface or where tectonic plates meet. As with igneous and sedimentary rocks, metamorphic rocks are classified on the basis of texture (grain size, shape, orientation) and mineral composition. 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. The texture of metamorphic rocks is foliated due to pressure. (Source: Belinda Madsen) 6.2.1 Foliation and Lineation. grains too small to see without a microscope, but rock isn't glassy. Texture of a rock is the appearance of the rock and how one feels touching it. even in the microscope, individual crystals cannot be discerned. Gneiss rocks exhibit a unique form of foliation known as gneissic banding, which are thicker bands of foliation than most metamorphic rocks display. Some examples of non-foliated metamorphic rocks are marble, quartzite, and hornfels. #2. Schist is finely foliated whereas gneiss is organized in noticeable, wide bands of minerals. Grain sizes 3. Marble is metamorphosed limestone. The rate of crystal growth is another factor, and that's how quickly new constituents come to the surface of the growing crystal. • Texture – microscopic to small-scale mesoscopic features of the rock produced by: 1. The dark bands are amphibole-rich, the light bands are feldspar-rich. individual crystals require a hand lens to discern. Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. These rocks are formed by the settling down of sediments. Metamorphic Rocks. (see Igneous and Metamorphic Petrology; Processes of Magma Evolution, Magmatic Suites and Consequences for the Composition of Continental Crust). Textures /structures of metamorphic rocks. Basalt is an example of extrusive igneous rocks. Some rocks may even appear to be non-foliated and banded. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, and their appearance. The size and shape of the mineral grains or crystals and the pattern of their arrangement give a texture to the rock. Metamorphic rocks are rocks that have changed from igneous rocks or metamorphic rocks. These terms describe the rock; for specific minerals in a rock description, you would give measurements in mm or cm. Terms other than “porphyritic” can be applied to the whole rock, or the groundmass around the phenocrysts (but not to individual minerals). Metamorphic rocks typically have different mineral assemblages and different textures from their parent rocks (Figure 7.1) but they may have the same overall composition. Even if a complex assemblage is not identifiable at the wellsite, a combination of minerals and textures should allow the rock to be characterized. Metamorphic rocks are classified by texture and by mineral composition. Mesh texture In olivine-rich rocks such as dunites and peridotites, serpentinization may or may not be complete. 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