It is a very dense polymorphic form of quartz that is stable at room temperatures only at pressures above 20,000 bars. Clays may be classified by use, origin, mineral composition, or color.Ĭoesite - A monoclinic mineral, SiO 2. 2) An earthy, extremely fine-grained sediment or soft rock composed primarily of clay-size or colloidal particles, having high plasticity and a considerable content of clay minerals. This is approximately the upper limit of size of particle that can show colloidal properties. The most common cements are silica, carbonates, and iron oxides.Ĭlast - An individual constituent, grain, or fragment of a detrital sediment or sedimentary rock, produced by the physical disintegration of a larger rock mass.Ĭlay - 1) A detrital mineral particle of any composition having a diameter less than 1/256 millimeter (4 microns). Calcite and aragonite (CaCO 3 ) are examples of carbonates.Ĭavity - A solutional hollow, often found in a limestone cave or in cavernous lava.Ĭement - Chemically precipitated mineral material that occurs in the spaces of a sedimentary rock, thus binding the grains into a rigid mass. Sometimes spelled cañon.Ĭarbonate - A mineral compound characterized by a fundamental anionic structure of CO 3 -2. Canyons are characteristic of arid or semiarid regions where downcutting by streams greatly exceeds weathering. Commonly gray or white, it has perfect rhombohedral cleavage and reacts readily with cold dilute hydrochloric acid.Ĭaldera - A large basin-shaped volcanic depression, more or less circular, the diameter of which is many times greater than that of the included ventor vents, irrespective of steepness of the walls or form of the floor.Ĭanyon - A stream-cut chasm or gorge, the sides of which are composed of cliffs or a series of cliffs rising from its bed. Most asteroid orbits are between those of planets Mars and Jupiter.īasalt - A dark colored igneous rock, commonly extrusive, composed primarily of calcic plagioclase and pyroxene the fine-grained equivalent of gabbro.īedrock - The solid rock that underlies gravel, soil, or other surficial material.īioherm - A mound-like or circumscribed mass of rock built by sedentary organisms such as corals, stromatoporoids, or algae, and enclosed in rock of different lithological character.īreccia - A coarse-grained clastic rock, composed of angular broken rock fragments held together by a mineral cement or a fine-grained matrix.Ĭalcite - A common rock-forming mineral, CaCO 3. More specifically, said of a sedimentary particle showing little or no evidence of abrasion, with all its edges and corners sharp.Īsh Fall - A rain of airborne volcanic ash falling from an eruption cloud.Īsteroid - One of the many small celestial bodies in orbit around the sun. They range in size from simple unicelluar forms to giant kelps several meters long, and display extremely varied life cycles and physiological processes, with, for example, different complexes of photosynthetic pigments.Īlluvial Fan - An outspread, gently sloping mass of alluvium deposited by a stream in an arid or semi-arid region where a stream issues from a narrow canyon onto a plain or valley floor.Īngular - Having sharp angles or borders. Any of several hard, inert materials, such as sand, gravel, slag, or crushed stone, used for mixing with a cemeting or bituminous material to form concrete, mortar, or plater or used alone, as in railroad ballast or graded fill.Īlgae - Photosynthetic, almost exclusively aquatic plants of a large and diverse group, including seaweeds and their fresh-water allies. Aggregate - A mass or body of rock particles, mineral grains, or both.
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