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Greywacke or graywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size lithic fragments set in a compact, clay-fine matrix.
Lithic sandstones can have a speckled (salt and pepper) or gray color, and are usually associated with one specific type of lithic fragment (i.e., igneous, sedimentary, or metamorphic). [ 1 ] Tectonically, lithic sandstones often form in a wide variety sedimentary depositional environments (including fluvial , deltaic , and alluvial sediments ...
Arkose – Type of sandstone containing at least 25% feldspar; Banded iron formation – Layered iron-rich sedimentary rock; Breccia – Rock composed of angular fragments; Calcarenite – Type of limestone that is composed predominantly of sand-size grains; Chalk – Soft carbonate rock
Stockton Sandstone: in western New Jersey along the Delaware River Potsdam Sandstone : in upstate New York Tapeats Sandstone : in Arizona (famously found in the Grand Canyon)
Tremolite is a member of the amphibole group of silicate minerals with composition Ca 2 (Mg 5.0-4.5 Fe 2+ 0.0-0.5)Si 8 O 22 (OH) 2.Tremolite forms by metamorphism of sediments rich in dolomite and quartz, and occurs in two distinct forms, crystals and fibers.
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar ) or more, causing profound physical or chemical changes.
The grey and white crystals are quartz and (limited) feldspar. Metamorphism is the transformation of existing rock (the protolith ) to rock with a different mineral composition or texture . Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids ...
Greenschist is defined by the presence of the minerals chlorite, epidote, or actinolite, which give the rock its green color. Greenschists also have pronounced schistosity . [ 3 ] Schistosity is a thin layering of the rock produced by metamorphism (a foliation ) that permits the rock to easily be split into flakes or slabs less than 5 to 10 ...