texture and structure of metamorphic rocks

Metamorphic Microstructures. PLAY. Throughout their cooling history all magmatic rocks try to achieve mechanical and chemical equilibrium, but rarely succeed. These terms describe the rock; for specific minerals in a rock description, you would give measurements in mm or cm. 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. The rate of crystal growth is another factor, and that's how quickly new constituents come to the surface of the growing crystal. Structure and Texture Anastasia Neni Metamorphic structure • Foliation; planar rock fabric (e.g. When it forms, the calcite crystals tend to grow larger, and any sedimentary textures and fossils that might have been present are destroyed. 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. Schist is finely foliated whereas gneiss is organized in noticeable, wide bands of minerals. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of these rocks. Allothimorph —a constituent of a metamorphic rock that has not changed its original crystal outline. burial, regional metamorphic rocks) – Slaty cleavage – Phyllitic – Schistose – Gneissose – Mylonitic • Non Foliation; equidimentional rock fabric (e.g. Texture of a rock is the appearance of the rock and how one feels touching it. Non-foliated rocks occur when heat is high, but pressure is low or equal on all sides. If a rock is foliated, its name is determined by the type of foliation present and the dominant minerals—for example, a kyanite schist. #2. Metamorphic texture is the description of the shape and orientation of mineral grains in a metamorphic rock. Others have a more isotropic arrangement of mineral grains. The nomenclature of metamorphic rocks is classified according to various criteria, especially texture, composition, and P–T conditions of metamorphism. If the minerals are segregated into alternating light‐colored and dark‐colored layers, the rock is called a gneiss. STUDY. Metamorphic Structures and Textures • Structure – features that characterize handspecimen or larger masses of rock. Sedimentary Rocks. aphanitic. grains visible with the unaided eye. 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. Metamorphic rock is classified by texture and composition. The texture of sedimentary rocks depends on their clast, age, and depositional setting. The texture of metamorphic rocks is foliated due to pressure. 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 rock possessing slaty cleavage has a unique property of splitting into thin sheets. Other factors include the diffusion rate, which is how atoms and molecules move through the liquid. Terms other than “porphyritic” can be applied to the whole rock, or the groundmass around the phenocrysts (but not to individual minerals). (Source: Belinda Madsen) 6.2.1 Foliation and Lineation. Rock microstructure includes the texture of a rock and the small scale rock structures. individual crystals require a hand lens to discern. 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. Metamorphic Rocks. The dark bands are amphibole-rich, the light bands are feldspar-rich. Metamorphic rocks are the third great class of rocks. This is a set of photomicrographs illustrating metamorphic textures, arranged as a slide show. Start studying Lab 5 - Textures and Structures of Rocks II. The words "texture" and "microstructure" are interchangeable, with the latter preferred in modern geological literature. Mesh texture In olivine-rich rocks such as dunites and peridotites, serpentinization may or may not be complete. Sediments are the smaller particles / fragments that are formed by the breaking … The texture of a metamorphic rock is a unique product of its mineralogy and metamorphic conditions. Such features include folds, nappes, and faults with a wide variety of geometries. The size and shape of the mineral grains or crystals and the pattern of their arrangement give a texture to the rock. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Textures. Earth Sciences 2: Introduction to Metamorphic Rocks. First, is the fact that metamorphism takes place through heat, pressure, and chemically … 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 exhibit a variety of textures. Metamorphic rock identification table. They have a very fine grained structure. 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. Foliation is a term used that describes minerals lined up in planes. (see Igneous and Metamorphic Petrology; Processes of Magma Evolution, Magmatic Suites and Consequences for the Composition of Continental Crust). Like water cycle, there exist rock cycle (geological cycle) in geology. Slate. Some rocks may even appear to be non-foliated and banded. 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. Changed from igneous rocks or metamorphic rocks whose normal structure … metamorphic rocks a property... 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