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GLG 101
Geology Terms
| Question | Answer |
|---|---|
| Abyssal plain | very level area of the deep-ocean floor, usually lying at the foot of the continental rise |
| Asthenosphere | a subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed |
| Catastrophism | the concept that Earth was shaped by catastrophic events of a short-term nature |
| Continental margin | that portion of the seafloor adjacent to the continents. It may include the continental shelf, continental slope, and continental rise |
| Continental rise | the gently sloping surface at the base of the continental slope |
| Continental shelf | the gently sloping submerged portion of the continental margin extending from the shoreline to the continental slope |
| Continental slope | the steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf |
| Core | the innermost layer of Earth based on composition. It is thought to be largely and iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur |
| Craton | that part of the continental crust that has attained stability; that is, it has not been affected by significant tectonic activity during the Phanerozoic eon. It consists of the shield and stable platform |
| Crust | the very thin outermost layer of Earth |
| Deep ocean basin | the portion of seafloor that lies between the continental margin and the oceanic ridge system. This region comprises almost 30% of Earth's surface |
| Deep ocean trench | a narrow, elongated depression of the seafloor |
| Fossil succession | fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content |
| Geology | the science that examines Earth, its form and composition, and the changes that it has undergone and is undergoing |
| Hypothesis | a tentative explanation that is then tested to determine if it is valid |
| Igneous rock | rock formed from the crystallization of magma |
| Inner core | the solid inner most layer of Earth, about 1216 kilometers (754 miles) in radius |
| Lithosphere | the ridged outer layer of Earth, including the crust and upper mantle |
| Lower mantle (mesosphere) | the part of the mantle that extends from the core to the mantle boundary to a depth of 660 kilometers |
| Mantle | one of Earth's compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 kilometers |
| Metamorphic rock | rock formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids |
| Oceanic ridge (mid-ocean ridge) | a continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300-3000 miles). The rifts at the crests of these ridges represent divergent plat boundaries |
| Outer core | a layer beneath the mantle about 2270 kilometers (1410 miles) thick, which ahs the properties of a liquid |
| Relative dating | rocks and structures are placed in their proper sequence or order. Only the chronological order of events is determined |
| Rock cycle | a model that illustrates the origin of the three basic rock types and the interrelatedness of Earth materials and processes |
| Sedimentary rock | rock formed from the weathered products of preexisting rocks that have been transported, deposited, and lithified |
| Shield | a large, relatively flat expanse of ancient igneous and metamorphic rocks within the craton |
| Stable platform | that part of the craton that is mantled by relatively undeformed sedimentary rocks and underlain by a basement complex of igneous and metamorphic rock |
| Law of Superposition | in any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below |
| System | a group of interacting or interdependent parts that form a complex whole |
| Theory | a well-tested and widely accepted view that explains certain observable facts |
| Uniformitarianism | the concept that the processes that have shaped Earth in the geologic past are essentially the same as those operating today |
| Atom | the smallest particle that exists as an element |
| Chemical compound | a substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements |
| Cleavage | the tendency of mineral to break along planes of weak bonding |
| Color | a phenomenon of light by which otherwise identical objects may be differentiated |
| Law of Constancy of Interfacial Angles | a law stating that the angle between equivalent faces of the same mineral are always the same |
| Covalent bond | a chemical bond produced by the sharing of electrons |
| Crystal | any natural solid with an ordered, repetitive atomic structure. Generally refers to a single mineral displaying geometrically related faces |
| Crystalline | any natural solid with and ordered, repetitive atomic structure |
| Crystal shape | characteristic combination of intersecting faces typical of specific crystalline materials |
| Electron | a negatively charged subatomic particle that has a negligible mass and is found outside and atom's nucleus |
| Element | a substance that cannot be decomposed into simpler substances by ordinary chemical or physical means |
| Fracture | the tendency of a mineral to break randomly, in the absence of planes of weak bonding |
| Hardness | a mineral's resistance to scratching and abrasion |
| Ion | an atom or molecule that possess and electrical charge |
| Ionic bond | a chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to the other |
| Isotopes | variety of the same element that have different mass numbers; their nuclei contain the same number of protons but different number of neutrons |
| Luster | the appearance or quality of light reflected from the surface of a mineral |
| Metallic bond | a chemical bond present in all metals that may be characterized as an extreme type of electron sharing in which the electrons move freely from atom to atom |
| Mineral | a naturally occurring, inorganic crystalline material with a unique chemical structure |
| Mohs scale | a series of 10 minerals used as a standard in determining hardness |
| Radioactive decay | the spontaneous decay of certain unstable atomic nuclei |
| Rock | a consolidated mixed of minerals |
| Silicate | any one of numerous minerals that have the silicon-oxygen tetrahedron as their basic structure |
| Silicon-oxygen tetrahedron | a structure composed of four oxygen atoms surrounding a silicon atom that constitutes the basic building block of silicate minerals |
| Specific gravity | the ratio of a substance's weight to the weight of any equal volume of water |
| Streak | the color of a mineral in powdered form |
| Tenacity | describes a mineral's toughness or its resistance to breaking or deforming |
| Unit cell | the basic building block of crystalline solids; the smallest unit that exhibits the physical and chemical properties o the particular mineral |
| Andesite | a fine-grained igneous rock with an intermediate composition |
| Aphanitic texture | a texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope |
| Basalt | a fine-grained igneous rock of mafic composition |
| Bowen's Reaction Series | a concept by N.L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks |
| Crystallization | the formation and growth of a crystalline solid from a liquid or gas |
| Crystal settling | during the crystallization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber |
| Decompression melting | melting that occurs as rock ascends due to a drop in confining pressure |
| Diorite | a granular igneous rock consisting essentially of plagioclase,feldspar, and hornblende |
| Extrusive | igneous activity that occurs at Earth's surface |
| Felsic | a compositional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicates |
| Fragmental texture | an igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption |
| Gabbro | a coarse-grained igneous rock of mafic composition |
| Geothermal gradient | the gradual increase in temperature with depth in the crust. The average is 30oC per kilometer in the upper crust |
| Glassy texture | a term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals |
| Granite | a coarse-grained igneous rock of felsic composition |
| Groundmass | the matrix of smaller crystals within an igneous rock that has porphyritic texture |
| Igneous rocks | rock formed from the crystallization of magma |
| Intermediate composition | a compositional group of igneous rocks, indicating that the rock contains at least 25% dark silicate minerals. The other dominate mineral is plagioclase feldspar |
| Intrusive | igneous rock that formed below Earth's surface |
| Lava | magma that reaches Earth's surface |
| Mafic | a compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar |
| Magma | a body of molten rock found at depth, including any dissolved gases and crystals |
| Magma mixing | the process of altering the composition of magma through the mixing of material from another magma body |
| Magmatic differentiation | the process of generating more than one rock type from a single magma |
| Melt | the liquid portion of magma excluding the solid crystals |
| Obsidian | volcanic glass, usually of silica-rich composition |
| Partial melting | process which most igneous rocks melt individual minerals have different melting points, most melt over a temperature range of a few hundred degrees. If liquid is squeezed out after some melting has occurred, a melt with a higher silica content results. |
| Pegmatitic texture | a texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter |
| Phaneritic texture | an igneous rock texture in which the crystals are roughly equal in size and large enough so that individual minerals can be identified without the aid of a microscope |
| Phenocryst | conspicuously large crystal embedded in a matrix of finer-grained crystals |
| Plutonic | igneous rocks that form at dept. After Pluto, the god of the lower world in classical mythology |
| Porphyritic texture | an igneous rock texture characterized by two distinctively different crystals sizes |
| Pyroclastic texture | an igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption |
| Rhyolite | a fine-grained rock of felsic composition |
| Texture | the size, shape, and distribution of the particles that collectively constitute a rock |
| Tuff | a pyroclastic igneous rock composed of tiny ash-sized fragments |
| Ultramafic | a compositional group of igneous rocks containing mostly olivine and pyroxene |
| Vesicular texture | a term applied to Aphanitic igneous rocks that contain many small cavities called vesicles |
| Volcanic | pertaining to the activities, structures, or rock types of a volcano |
| Welded tuff | a pyroclastic igneous rock in which the ash-sized fragments have been fused (welded) together by remnant heat |
| Aa flow | a type of lava flow that has a jagged, blocky surface |
| Batholith | a large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion |
| Caldera | a large depression typically caused by collapse or ejection of the summit area of a volcano |
| Cinder cone | a rather small volcano built primarily of ejected lava fragments that consist mostly of pea to walnut-size lapilli |
| Columnar joints | a pattern of cracks that forms during cooling of molten rock to generate columns |
| Composite cone | a volcano composed of bother lava flows and pyroclastic material |
| Concordant | a term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock |
| Crater | a depression at the summit of a volcano |
| Dike | a tabular-shaped intrusive igneous feature that cuts through the surrounding rock |
| Discordant | a term used to describe plutons that cut across existing rock stuctures, such as bedding planes |
| Fissure | a crack in rock along which there is a distinct separation |
| Flood basalt | flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds o meters |
| Fumarole | a vent in a volcanic area from which fumes or gases escape |
| Laccolith | a massive igneous body intruded between preexisting strata |
| Lahar | debris flows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope usually following stream channels |
| Lava dome | a bulbous mass associated with old-age volcano, produced when thick lava is slowly squeezed from the vent |
| Lava tube | tunnel in hardened lava that acts as a horizontal conduit for lava flowing rom a volcanic vent |
| Nueé ardente | incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion |
| Pahoehoe flow | a lava flow with smooth-to-ropy surface |
| Pillow lava | basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows |
| Pluton | a structure that results from the emplacement and crystallization of magma beneath the surface of the Earth |
| Pumice | a light-colored glassy vesicular rock commonly having a granitic composition |
| Pyroclastic flow | a highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground |
| Scoria | vesicular ejecta that is the product of basaltic magma |
| Shield volcano | a broad, gently sloping volcano built from fluid basaltic lavas |
| Sill | a tabular igneous body that was intruded parallel to the layering of preexisting rock |
| Stock | a pluton similar to but small than a batholith |
| Stratovolcanoes | a volcano composed of bother lava flows and pyroclastic material |
| Vent | the surface opening of a conduit or pipe |
| Viscosity | a measure of the fluid's resistance to flow |
| Volcanic neck | an isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano |
| Volcano | a mountain formed from lava and/or pyroclastics |
| Volatiles | gaseous components of magma dissolved in the melt |
| Xenolith | an inclusion of unmelted country rock in an igneous pluton |
| Acid mine drainage | mine drainage water that has been rendered acidic by the chemical alteration of pyrite exposed by the mining process |
| Chemical weathering | the process by which the internal structure of a mineral is altered by the removal and/or addition of elements |
| Differential weathering | the variation in the rate and degree of weathering caused by such factors as mineral makeup, degree of jointing, and climate |
| Dissolution | a common form of chemical weathering, it is the process of dissolving into a homogeneous solution, as when an acidic solution dissolves limestone |
| Eluviation | the washing out of fine soil components from the A horizon by downward percolating water |
| Erosion | the incorporation and transportation of material by a mobile agent, such as water, wind, or ice |
| Exfoliation dome | large dome-shaped structure, usually composed of granite, formed by sheeting |
| Frost wedging | the mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices |
| Horizon | a layer in a soil profile |
| Humus | organic matter in soil produced by the decomposition of plants and animals |
| Hydrolysis | a chemical weathering process in which minerals are altered by chemically reacting with water and acids |
| Leaching | the depletion of soluble materials from the upper soil by downward percolating water |
| Mass wasting | the downslope movement of rock, regolith, and soil under the direct influence of gravity |
| Mechanical weathering | the physical disintegration of rock, resulting in smaller fragments |
| Oxidation | the removal of one or more electrons from an atom or ion |
| Parent material | the material upon which a soil develops |
| Regolith | the layer of rock and mineral fragments that nearly everywhere covers Earth's land surface |
| Sheeting | a mechanical weathering process characterized by the splitting off of slablike sheets of rock |
| Soil | a combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant growth |
| Soil profile | a vertical section through a soil, showing its succession of horizons and the underlying parent material |
| Soil taxonomy | a soil classification system consisting of six hierarchical categories based on observable soil characteristics |
| Spheroidal weathering | any weathering process that tends to produce a spherical shape from an initially blocky shape |
| Talus slope | an accumulation of rock debris at the base of a cliff |
| Weathering | the disintegration and decomposition of rock at or near the surface of Earth |
| Alluvial fan | a fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced |
| Asymmetrical ripple mark | a wave of sand formed by a directional water or wind current, so that the wave is tipped in the direction of the current |
| Angularity | a measure of the degree to which a sedimentary clast's edges and corners are rounded |
| Bedding plane | a nearly flat surface separating two beds of sedimentary rock, and marking the end of one deposit and beginning of another |
| Beds | parallel layers of sedimentary rock |
| Biochemical | a type of chemical sediment that forms when material dissolved in water is precipitated by water-dwelling organisms |
| Breccia | a poorly sorted detrital sedimentary rock composed of large angular clasts |
| Cementation | a type of Lithification in which precipitates from water percolated through the sediment, filling open spaces and joining particles into a solid mass |
| Chemical sedimentary rock | ions in a solution are precipitated by either organic or biologic processes (chemical weathering) |
| Chert | a chemical sedimentary rock composed of microcrystalline quartz |
| Clastic texture | a sedimentary rock texture consisting of broken fragments of preexisting rock |
| Clasts | mineral and rock fragment resulting from weathering |
| Coal | an organic sedimentary rock composed of carbon derived from plant debris |
| Compaction | lithification in which the weight of overlying material compresses more deeply buried sediment (fine-grained sedimentary rocks- shale) |
| Conglomerate | a poorly sorted detrital sedimentary rock composed of large rounded clasts |
| Crossbedding | structure in which relatively thin layers are inclined at an angle to the main bedding |
| Crystalline texture | a term for the texture of sedimentary rocks in which the minerals from a pattern of interlocking crystals |
| Deep marine environment | depositon environment that occupies the portion of the seafloor that lies between the continental margin and the oceanic ridge system |
| Delta environment | system of stream, swamp and terrestrial depositional environments occupying on the accumulated sediment where a stream enter a lake or ocean |
| Detrital sedimentary rock | rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanical and chemical weathering |
| Diagenesis | a collective term for all the chemical, physical, and biological changes that take place after sediments are deposited and during and after Lithification |
| Dolostone | a chemical sedimentary rock composed of mineral dolomite |
| Dune environment | depositional environment associated with dunes, or hill/ridges of wind-deposited sand |
| Environment of deposition | a geographic setting where sediment accumulates under a particular set of geologic processes and environmental conditions |
| Evaporite | a sedimentary rock formed of material deposited from solution by evaporation of water |
| Facies | a portion of a rock unit that possesses a distinctive set of characteristics that distinguishes it from other parts of the same unit |
| Fossil | the remains or traces of organisms preserved from the geologic past |
| Glacial environment | depositional environments associated with glaciers and glaciation |
| Graded bed | a sedimentary layer characterized by a decrease in sediment size from bottom to top |
| Limestone | a chemical sedimentary rock composed of mineral limestone |
| Lithification | the process, generally cementation and/or compaction, of converting sediments to solid rocks |
| Mudcrack | a feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks |
| Nonclastic texture | a term for the texture of sedimentary rocks in which the minerals form a pattern of interlocking crystals |
| Organic sedimentary rock | sedimentary rock composed of organic carbon from the remains of plants that died and accumulated on the floor of a swamp |
| Rounding | the reduction in the angularity of a sedimentary clast's edges and corners, usually by abrasion experienced during transportation |
| Salt flat | a white crust on the ground produced when water evaporates and leaves its dissolved materials behind |
| Sandstone | a detrital sedimentary rock composed of sand-sized particles |
| Sedimentary environment | a geographic setting where sediment accumulates under a particular set of geologic processes and environmental conditions |
| Sedimentary rock | a rock composed of the particles, precipitates, or organic debris resulting from the erosion, transportation and deposition of the products of weathering |
| Shale | a detrital sedimentary rock composed of silt and clay-sized particles |
| Shallow marine environment | system of depositional environments found between the shoreline and the continental rise |
| Sorting | the degree of similarity in particle size in sediment or sedimentary rock |
| Strata | parallel layers of sedimentary rock |
| Symmetrical ripple mark | the back and forth movement of surface waves in a shallow near shore environment (oscillation ripple marks) |
| Turbidity current | a downslope movement of water in and erratic fashion often characterized by swirling, whirlpool-like eddies |
| Aureole | a zone or halo of contact metamorphism found in the country rock surrounding and igneous intrusion |
| Burial metamorphism | low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata |
| Confining pressure | an equal, all-sided pressure |
| Contact metamorphism | changes in rock caused by the heat from a nearby magma body |
| Differential stress | forces that are unequal in different directions |
| Foliation | a term for linear arrangement of textural features often exhibited by metamorphic rocks |
| Gneiss | a high-grade foliated metamorphic rock with a banded appearance |
| Gneissic texture | A texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance |
| Hydrothermal metamorphism | chemical alterations that occur as hot, ion-rich water circulates through fractures in rock |
| Hydrothermal solution | the hot, watery solution that escapes from a mass of magma during the later stages of crystallization |
| Impact metamorphism | metamorphism that occurs when meteorites strike Earth's surface |
| Index mineral | a mineral that is a good indicator of the metamorphic environment in which it formed |
| Marble | an unfoliated metamorphic rock composed of calcite |
| Metamorphic facies | a group of associated minerals that are used to establish the pressures and temperature at which rocks undergo metamorphism |
| Metamorphism | the changes in mineral composition and texture of a rock subjected to high temperature and pressure with Earth |
| Metasomatism | a metamorphic change in composition by the interaction with fluids around magma body |
| Nonfoliated texture | a texture of metamorphic rocks in which there is no linear arrangement of textural features |
| Parent rock | the rock from which a metamorphic rock formed |
| Phyllite | gradation in the degree of metamorphism between slate and schist, glossy sheen, wavy texture, fine crystals of muscovite, chlorite |
| Quartzite | an unfoliated metamorphic rock composed of quartz |
| Regional metamorphism | metamorphism associated with large-scale mountain building |
| Rock cleavage | the tendency of rocks to split along parallel, closely spaced surfaces |
| Schist | a medium to coarse grained foliated metamorphic rock in which platy minerals are visible |
| Schistosity | a type of floatation characterized by parallel arrangement of platy minerals |
| Shield | a large, relatively flat expanse of ancient igneous and metamorphic rocks with the craton |
| Shock metamorphism | metamorphism caused when high-speed projectiles (meteorites) impact Earth |
| Slate | a low-grade foliated metamorphic rock that is fine-grained and composed of undiscernible platy minerals |
| Slaty cleavage | the type of foliation in which there is parallel arrangement of fine-grained metamorphic minerals |
| Texture | the size, shape, and distribution of the particles that collectively constitute a rock |
| Thermal metamorphism | changes in rock caused by the heat from a nearby magma body |
| Cap rock | an impermeable layer that constitutes and oil trap by preventing mobile oil and gas from escaping at the surface |
| Disseminated deposit | any economic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore |
| Fossil fuel | general term for any hydrocarbon that may be used as fuel, including coal, oil, natural gas, bitumen for tar sands, and shale oil |
| Geothermal energy | natural steam used for power generation |
| Hydroelectric power | electricity generated by falling water that is used to drive turbines |
| Hydrothermal solution | the hot, watery solution that escapes from a mass of magma during the latter stages of crystallization |
| Mineral resource | all discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future |
| Nonmetallic mineral resource | a mineral resource that is not a fuel or processed for the metals it contains |
| Nonrenewable resource | a mineral resource that forms or accumulates over such long time span that it must be considered as fixe in total quantity |
| Nuclear fission | the splitting of atomic nuclei into smaller nuclei, causing neutrons to be emitted and heat energy to be released |
| Oil trap | a set of impermeable layers and/or geologic structures that result in the accumulation of oil and gas |
| Ore | usually a useful metallic (and certain non-metallic) mineral that can be mined at a profit |
| Pegmatite | a very coarse-grained igneous rock commonly found as dike associated with a large mass of plutonic rock that has smaller crystals |
| Placer | deposit formed when heavy minerals are mechanically concentrated by currents, most commonly streams and waves |
| Renewable resource | a resource that is virtually inexhaustible or that can be replenished over relatively short time spans |
| Reserve | already identified deposits from which minerals can be extracted profitably |
| Reservoir rock | the porous, permeable portion of any oil trap that yields oil and gas |
| Secondary enrichment | the concentration of minor amounts of metals that are scattered through unweathered rock into economically valuable concentrations by weathering processes |
| Vein deposit | a mineral filling a fracture or fault in a host rock |
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