Metamorphic Rocks - Encyclopedia.com
Jun 11, 2018 · Metamorphic rock found closer to Earth's surface, or produced by low pressure, characteristically splits or flakes into layers of varying thickness. This is called foliation. Slate is often used as roofing tiles and paving stones. With lots of pressure and increasing heat, rock called schist forms.
Phyllite - Encyclopedia.com
May 9, 2018 · Phyllite is an intermediate-grade, foliated metamorphic rock type that resembles its sedimentary parent rock , shale, and its lower-grade metamorphic counterpart, slate . Like slate, phyllite can be distinguished from shale by its foliation, called slaty cleavage, and its brittleness, or fissility. Both slate and phyllite are generally dark ...
Schist - Encyclopedia.com
May 23, 2018 · schist A regional metamorphic rock of pelitic (see PELITE) composition which displays a schistosity. Schists are coarsergrained than phyllites, having a grain size greater than 1 mm. The minerals defining the schistosity may be muscovite mica, biotite mica, and/or elongate quartz, depending on the composition and the pressure and temperature of ...
Metamorphism - Encyclopedia.com
Jun 8, 2018 · metamorphism The process of changing the characteristics of a rock in response to changes in temperature, pressure, or volatile content. Most metamorphic changes do not include bulk chemical changes, but merely the crystallization of new mineral phases. These isochemical changes cause major textural changes.
Gneiss - Encyclopedia.com
Jun 8, 2018 · gneiss (adj. gneissose) General petrological term applied to coarse-grained, banded rocks that formed during high-grade regional metamorphism. The banding (gneissose banding, or gneissosity) is a result of the separation of dark minerals (e.g. biotite, hornblende, and pyroxenes) and the light-coloured quartzofeldspathic minerals. A gneissose ...
Hornfels - Encyclopedia.com
May 21, 2018 · Hornfels is a fine-textured metamorphic rock formed by contact metamorphism . Contact metamorphism occurs when a mass of hot magma intrudes into preexisting rock , whether by injecting itself into a crack or by ascending in a large body (e.g., pluton ). Rock in close proximity to the magma is temporarily softened or melted and recrystallizes ...
Greenstone - Encyclopedia.com
May 8, 2018 · greenstone A low-grade, regional metamorphic rock containing actinolite, epidote, and albite, and lacking a cleavage. Greenstones form by metamorphism of basic igneous rocks, the actinolite and epidote components being derived from the ferromagnesium minerals present in the original rock. Actinolite and epidote impart a green colour to the ...
Migmatite - Encyclopedia.com
May 29, 2018 · Migmatite. A migmatite, or "mixed rock" in Greek, is a banded, heterogenous rock composed of intermingled metamorphic and igneous components. Veins, contorted layers, and irregular pods of silica-rich granite occur within the structure of foliated iron and magnesium-rich metamorphic rocks like gneiss , schist and amphibolite.
Sedimentary Rock - Encyclopedia.com
May 17, 2018 · Sedimentary Rock. Sedimentary rocks form at or near Earth ’ s surface from the weathered remains of pre-existing rocks or organic debris. The term sedimentary rock applies both to consolidated, or lithified sediments (bound together, or cemented) and unconsolidated sediments (loose, like sand). Although there is some overlap, most sedimentary ...
Marble - Encyclopedia.com
May 18, 2018 · 1. a hard crystalline metamorphic form of limestone, typically white with mottlings or streaks of color, that is capable of taking a polish and is used in sculpture and architecture. ∎ used in similes and comparisons with reference to the smoothness, hardness, or color of marble: her shoulders were as white as marble. ∎ a marble sculpture.2 ...