Aggregate -- A mass or body of rock particles, mineral grains, or both. 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.
Algae -- Photosynthetic, almost exclusively aquatic plants of a large and diverse group, including seaweeds and their fresh-water allies. 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. Alluvial 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.
Angular -- Having sharp angles or borders. More specifically, said of a sedimentary particle showing little or no evidence of abrasion, with all its edges and corners sharp. Ash Fall -- A rain of airborne volcanic ash falling from an eruption cloud. Asteroid -- One of the many small celestial bodies in orbit around the sun. Most asteroid orbits are between those of planets Mars and Jupiter. Basalt -- A dark colored igneous rock, commonly extrusive, composed primarily of calcic plagioclase and pyroxene; the fine-grained equivalent of gabbro.
Bedrock -- The solid rock that underlies gravel, soil, or other surficial material. Bioherm -- 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.
Breccia -- A coarse-grained clastic rock, composed of angular broken rock fragments held together by a mineral cement or a fine-grained matrix. Calcite -- A common rock-forming mineral, CaCO 3. Commonly gray or white, it has perfect rhombohedral cleavage and reacts readily with cold dilute hydrochloric acid. Caldera -- 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.
Canyon -- A stream-cut chasm or gorge, the sides of which are composed of cliffs or a series of cliffs rising from its bed. Canyons are characteristic of arid or semiarid regions where downcutting by streams greatly exceeds weathering. Carbonate -- A mineral compound characterized by a fundamental anionic structure of CO 3 Calcite and aragonite CaCO 3 are examples of carbonates. Cavity -- A solutional hollow, often found in a limestone cave or in cavernous lava.
Cement -- Chemically precipitated mineral material that occurs in the spaces of a sedimentary rock, thus binding the grains into a rigid mass.
The most common cements are silica, carbonates, and iron oxides. Clast -- An individual constituent, grain, or fragment of a detrital sediment or sedimentary rock, produced by the physical disintegration of a larger rock mass.
This is approximately the upper limit of size of particle that can show colloidal properties. Clays may be classified by use, origin, mineral composition, or color. Coesite -- A monoclinic mineral, SiO 2. It is a very dense polymorphic form of quartz that is stable at room temperatures only at pressures above 20, bars. Found in impact craters and associated structures. Comet -- A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.
Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water. Complex Crater -- An impact crater that has a more irregular shape than a simple crater with a depth to diameter ratio near This type of crater has an uplift that forms in the center due to the earth rebounding from the impact event.
Crust -- The outermost layer of the Eart; that part of the Earth above the Mohorovicic discontinuity, made up of sial , or of sial and sima. It represents less than 0. Crystal -- A homogenous, solid body of a chemical element, compound, or isomorphous mixture, having a regularly repeating atomic arrangement that may be outwardly expressed by plane faces.
Deformation -- A general term for the processes of folding, faulting, shearing, compression, or extension of rocks as a result of various earth forces. Datum -- A fixed or assumed point, line, or surface, in relation to which others are determined. Delta -- The nearly flat alluvial tract of land at the mouth of a river, commonly forming a triangular or fan-shaped plain resembling the greek letter "delta" in plan view.
It is crossed by many distributaries, and results from the accumulation of sediment supplied by the river. Desert -- A region with a mean annual precipitation of 10 inches or less, and so devoid of vegetation as to be incapable of supporting any considerable population. Four kinds may be distinguished: 1 polar deserts, marked by perpetual snow cover and intense cold; 2 middle-latitude deserts, in the basinlike interiors of the continents, such as the Gobi, characterized by scant rainfall and high summer temperatures; 3 trade-wind deserts, notably the Sahara, with negligible precipitation and large daily temperature range; 4 coastal deserts, as in Peru, where there is a cold current on the western coast of a large land mass.
Dune -- A mound, ridge, or hill of wind-blown sand, either bare or covered with vegetation. Ejecta -- Glass, rock fragments, and other material thrown out of an explosion or impact crater during formation.
Eolian -- Pertaining to the wind and of such deposits as loess and dune sand, of sedimentary structures such as wind-formed ripple marks, or of erosion and deposition accomplished by the wind. Fault -- A fracture or a fracture zone along which there has been displacement of the sides relative to one another parallel to the fracture. Fault plane -- A fault surface that is more or less planar. The term is used in a relative sense, and various size limits have been utilized.
Formation -- 1. A body of rock strata that consists dominantly of a certain lithologic type or combination of types. It is the fundamental lithostratigraphic unit. Formations may be combined into groups or subdivided into members. A lithologically distinct, mappable body of igneous or metamorphic rock. An informal term applied by drillers to a sedimentary rock with certain drilling characteristics, e.
A group of plant or animal associations that exist together because of closely similar life patterns, habits, and climate requirements. A topographic feature differing conspicously from adjacent features, e. A speleothem. Fossil -- Any remains, trace, or imprint of a plant or animal that has been preserved in the earth's crust since some past geologic or prehistoric time; loosely, any evidence of past life. Fracture -- A crack, joint, or other break in rocks.
Glacier -- A large mass of ice formed on land by the compaction and recrystallization of snow, creeping downslope or outward due to the stress of its own weight, and surviving from year to year.
Glass -- A state of matter intermediate between the close-packed, highly ordered array of a crystal, and the poorly-packed, highly disordered array of a gas. Most glasses are supercooled liquids, i. The distinction between glass and liquid is on the basis of viscosity.
Gneiss -- A foliated rock formed by regional metamorphism, in which bands or lenticles of granular minerals alternate with bands or lenticles of minerals with flaky or elongate prismatic habit. Broadly applied, any holocrystalline quartz-bearing plutonic rock. Gravel -- 1 An unconsolidated natural accumulation of rounded rock fragments, mostly of particles larger than sand diameter greater than 2 millimeters , such as boulders, cobbles, pebbles, granules, or any combination of these; the unconsolidated equivalent of a conglomerate.
It is the commonest sulfate mineral, and is frequently associated with halite and anhydrite in evaporites, forming thick, extensive beds, especially in rocks of Permian and Triassic age. Hydrothermal -- Of or pertaining to hot water, to the action of hot water, or to the products of this action, such as a mineral deposit precipitated from a hot aqueous solution; also said to be the solution itself.
This term is generally used for any hot water, but has been restricted by some to water of magmatic origin. Igneous-- Said of a rock or mineral that solidified from molten or partly molten material, i. Igneous rocks constitute one of the three main classes into which rocks are divided, the others being metamorphic and sedimentary. Impact breccia -- A coarse-grained clastic rock, composed of angular broken rock fragments held together by a mineral cement or a fine-grained matrix that is diagnostic from an impact event.
Impact melt breccia -- A coarse-grained clastic rock, composed of angular broken rock fragments held together by a mineral cement or a fine-grained matrix of crystallized impact melt that is diagnostic from an impact event.
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