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This article discusses how rocks are formed. There are also articles on physical rock formations, rock layerings , and the formal naming of geologic formations. Terrestrial rocks are formed by three main mechanisms: Sedimentary rocks are formed through the gradual accumulation of sediments: for example, sand on a beach or mud on a river bed. As ...
It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects. Rocks are usually grouped into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are formed when magma cools in the Earth's crust, or lava cools
Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks, and volcanic rocks. Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes. [11]
A thunderegg (or thunder egg) is a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. [1] Thundereggs are rough spheres, most about the size of a baseball—though they can range from a little more than a centimeter (one half inch) to over a meter (three feet) across.
Skarn – Hard, coarse-grained, hydrothermally altered metamorphic rocks; Slate – Metamorphic rock - A low grade metamorphic rock formed from shale or silts; Suevite – Rock consisting partly of melted material formed during an impact event – A rock formed by partial melting during a meteorite impact
The rocks are deformed in a number of different ways: by erosion and weathering, glacial action, or from a sudden disturbance. Mushroom rocks are related to, but different from, yardang. [1] A mushroom rock, rock pedestal, or gour is a typical mushroom-shaped landform that is formed by the action of wind erosion. At an average height of two to ...
These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian, however the most common fine-grained rock would be known as basalt. Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks. [2]
Uluru (Ayers Rock) is a large sandstone formation in Northern Territory, Australia.. Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical (biogenic) sedimentary rocks, chemical sedimentary rocks, and a fourth category for "other" sedimentary rocks formed by impacts, volcanism, and other minor processes.