Glossary / Science

Geology Glossary

A-Horizon: The uppermost layer of a soil, containing organic material and leached minerals.
Aa: A blocky and fragmented form of lava occurring in flows with fissured and angular surfaces.
Acidic Rock: An igneous rock that has a relatively high silica content. Examples are granite and rhyolite. Also s
Acquisition: Obtaining the legal right to test a property for mineral resources and produce any that are discover
Acre-Foot: The volume of water needed to flood one acre of land to a depth of one foot. Equivalent to 43,560 cu
Acreage: An area, measured in acres, that is owned or controlled by one or more owners or lessees. "Gross Acr
Algal Mat: A layered communal growth of algae observed in fossils an in present day tidal zones associated with
Alkali: Used in reference to materials that are rich in sodium and/or potassium.
Alkali Metal: A strongly basic metal like potassium or sodium.
Alluvial Fan: A fan-shaped wedge of sediment that typically accumulates on land where a stream emerges from a stee
Alluvium: Unconsolidated terrestrial sediment composed of sorted or unsorted sand, gravel, and clay that has b
Amphibolite: Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions
Andesite: A fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as ho
Angle Of Repose: The maximum angle that a soil, sediment or other loose material can be placed or accumulate and be s
Angstrom: A length of 10 to the minus tenth meter or one hundred millionth of a centimeter.
Angular Unconformity: An erosional surface that separates rock units of differing dips. The rocks below the surface were d
Anthracite: The highest rank of coal. By definition, a coal with a fixed carbon content of over 91% on a dry ash
Aquiclude: A subsurface rock, soil or sediment unit that does not yield useful quanties of water.
Aquifer: A subsurface rock or sediment unit that is porous and permeable. To be an aquifer it must have these
Aquifer (Artesian): An aquifer that is bounded above and below by impermeable rock or sediment layers. The water in the
Aquifer (Confined): An aquifer that is bounded above and below by impermeable rock or sediment layers. There may or may
Aquifer (Unconfined): An aquifer that is not overlain by an impermeable rock unit. The water in this aquifer is under atmo
Arkose: A sandstone that contains at least 25% feldspar. Easily recognized because the feldspar grains are t
Arroyo: A steep-sided and flat-bottomed gulley in an arid region that is occupied by a stream only intermitt
Artesian Well: A well that penetrates an aquiclude to reach an aquifer containing water under pressure. Thus water
Asthenosphere: A portion of the upper mantle that is directly below the lithosphere. A zone of low strength in the
Astrobleme: An ancient circular scar on Earth's surface produced by the impact of a meteorite or comet. Use our
Atmosphere (Unit): A unit of pressure equal to 101,325 newtons per square meter, or about 14.7 pounds per square inch.
Atoll: A ring-shaped group of coral islands that are surrounded by deep ocean water and that enclose a shal
B-Horizon: The intermediate layer in a soil, situated below the A-horizon and consisting of clays and oxides. A
Backwash: The seaward rush of water down a beach that occurs with a receding wave.
Banded Iron Ore: A rock that consists of alternating layers of chert and iron oxide mineral (usually hematite) with t
Bank Storage: Water that seeps into the ground along the banks of a stream during a time of high flow. This loss o
Bankfull Stage: A height of water in a stream that completely fills the natural channel. If the water rises any high
Bar: An underwater ridge, usually of sand and/or gravel, that forms from the deposition and reworking of
Bar (Stream): An accumulation of sediment, usually sandy, which forms at the borders or in the channels of streams
Bar-Finger Sand: An elongated lens of sand deposited during the growth of a distributary in a delta. The bar at the d
Barchan: A sand dune that is crescent-shaped in map view. Barchan dunes form in areas of limited sand supply.
Barrier Island: A long, narrow island parallel to the shore, composed of sand and built by wave action.
Basalt: A dark-colored fine-grained extrusive igneous rock composed largely of plagioclase feldspar and pyro
Base Flow: Water that seeps into a stream through a permeable rock or sediment unit that outcrops in the bottom
Base Level: The lower limit of erosion by a stream. Sea level is the ultimate base level. However, lakes can ser
Basement: The oldest rocks recognized in a given area, a complex of metamorphic and igneous rocks that underli
Basic Rock: An igneous rock that has a relatively low silica content. Examples are gabbro and basalt. Also see e
Basin: In tectonics, a circular, syncline-like depression of strata. In sedimentology, the site of accumula
Batholith: A great irregular mass of coarse-grained igneous rock with an exposed surface of more than 100 squar
Bathymetry: The measurement of ocean depths and the preparation of topographic maps of the ocean floor.
Bauxite: The principal ore of aluminum. A mixture of aluminum oxides and hydroxides that forms from intense c
Bed Load: The larger, heavier particles that are being transported by a stream. Instead of being dissolved or
Bed-Load: The sediment that a stream moves along the bottom of its channel by rolling and bouncing.
Bedding: The characteristic structure of sedimentary rocks in which layers of different composition, grain si
Bedding Plane: A distinct surface of contact between two sedimentary rock layers.
Bedrock: Solid rock present beneath any soil, sediment or other surface cover. In some locations it may be ex
Beta-Particle: An electron emitted with high energy and velocity from the nucleus of an atom during radioactive dec
Biochemical Precipitate: A sediment, especially of limestone or iron, formed from elements extracted from seawater by living
Biochemical Rocks: A sedimentary rock that forms from the chemical activities of organisms. Organic (reef and fossilife
Bioturbated: An adjective used in reference to a sediment or sedimentary rock. Bioturbated sediments have been di
Bituminous Coal: A rank of coal that falls between anthracite and semi-bituminous. The most abundant rank of coal. Fr
Block Fault: A structure formed when the crust is divided into blocks of different elevation by a set of normal f
Block Fault Mountain: A linear mountain that is bounded on both sides by normal faults.
Blowout: A shallow, round or trough-shaped depression in sand or dry soil that is formed by wind erosion. The
Bolson: In arid regions, a basin filled with alluvium and intermittent playa lakes and having no outlet.
Bond: The force that holds together two atoms in a compound. It may be derived from the sharing of electro
Breccia: A clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragment
Butte: A conspicuous hill with steep sides and a flat top. The top is usually a cap-rock of resistant mater
C-Horizon: The lowest horizon of a soil profile. It is below the B-horizon and is made up of weathered bedrock.
Caldera: A large, bowl-shaped crater associated with a volcanic vent. A caldera can form from a volcanic blas
Carbonate Ion: The anion group CO3 with a charge of minus two.
Carbonate Platform: A submarine or intertidal shelf whose elevation is maintained by active shallow water carbonate depo
Carbonate Rock: A rock made up primarily of carbonate minerals (minerals containing the CO3 anionic structure). Lime
Carbonic Acid: A weak acid (H2CO3) that forms from the reaction of water and carbon dioxide. Most rain water is a v
Carrying Costs: The costs incurred by a lessee to retain exploration and property rights after acquisition but befor
Cataclastic Rock: A breccia of powdered rock formed by crushing and shearing during tectonic movements.
Cation: Any ion with a positive electric charge.
Cement: A solid precipitate of calcium carbonate, silica, iron oxide, clay minerals or other materials that
Cementation: The processes through which chemical precipitates form within the pore spaces of a sediment and help
Central Vent: The largest vent of a volcano, situated at the center of its cone.
Chemical Sediment: One that is formed at or near its place of deposition by chemical precipitation, usually from seawat
Chemical Sedimentary Rock: A rock that forms from the precipitation of mineral material from solution. Examples are chert and r
Chemical Weathering: The breaking down of surface rock material by solution or chemical alteration. Common alteration pro
Chert: A microcrystalline or cryptocrystalline sedimentary rock material composed of SiO2. Occurs as nodule
Christmas Tree: The valves, pipes and fittings installed above ground surface at an oil or gas well site. These cont
Cinder Cone: A steep, conical hill built up about a volcanic vent and composed of coarse pyroclasts expelled from
Cirque: The head of a glacial valley, usually with the form of one half of an inverted cone. The upper edges
Clastic: A sedimentary rock (such as shale, siltstone, sandstone or conglomerate) or sediment (such as mud, s
Clastic Rock: A sedimentary rock formed from mineral particles (clasts) that were mechanically transported.
Clay: A clastic mineral particle of any composition that has a grain size smaller than 1/256 mm. The term
Coal: A brown or black sedimentary rock that forms from accumulated plant debris. A combustible rock that
Coal Gasification: The process of converting solid coal into gas, usually by heating. The gas is then used as a fuel or
Coal Liquefaction: The process of converting solid coal into a liquid fuel such as synthetic crude oil or methanol.
Coastal Plain: An area of low relief along a continental margin that is underlain by thick, gently dipping sediment
Compaction: A compression process that reorients and reshapes the grains of a sediment in response to the weight
Composite Cone: A cone-shaped volcanic mountain composed of alternating layers of cinders and lava flows. Also known
Cone Of Depression: A cone-shaped lowering of the water table around a producing well.
Conglomerate: A clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded pa
Contact Metamorphism: Mineralogical and textural changes and deformation of rock resulting from the head and pressure of a
Contour Line: A line on a map that traces locations where the value of a variable is constant. For example, contou
Contour Map: A map that shows the change in value of a variable over a geographic area through the use of contour
Crude Oil: A liquid hydrocarbon produced from natural underground reservoirs. It might also include liquid hydr
Cubic Feet Per Second: A unit of measure frequently used to quantify the rate of flow of a stream. It is equal to a volume
Datum: A reference location or elevation which is used as a starting point for subsequent measurements. Sea
Datum Plane: An artificially established, well surveyed horizontal plane against which elevations, depths, tides,
Daughter Element: Also 'daughter product'. An element that occurs in a rock as end product of the radioactive decay of
Debris Avalanche: The sudden downslope movement of rock and soil on a steep slope.
Declination: At any place on Earth, the angle between the magnetic and rotational poles.
Decollment: A horizontal to subhorizntal fault or shear zone with a very large displacement. The rocks above the
Deflation: The removal of clay- and silt-size particles from a soil by wind erosion. The term can also be used
Delay Rental: A payment to a mineral rights owner by a lessee if commercial production does not begin according to
Delta: A deposit of sediment that forms where a stream enters a standing body of water such as a lake or oc
Delta Kame: A deposit having the form of a steep, flat topped hill, left at the front of a retreating continenta
Dendritic Drainage: A stream drainage pattern that resembles the veins of a leaf in map view. Occurs mainly where the ro
Density: The mass per unit volume of a substance, commonly expressed in grams/ cubic centimeter.
Density Current: A gravity-driven flow of dense water down an underwater slope. The increased density of the water is
Deposition: The settling from suspension of transported sediments. Also, the precipitation of chemical sediments
Deposition Remnant Magnetization: A weak magnetization created in sedimentary rocks by the rotation of magnetic crystals into line wit
Desert Pavement: A ground cover of granule-size and larger particles that is typically found in arid areas. This grou
Detrital: A word used in reference to sediments or sedimentary rocks that are composed of particles that were
Detrital Sediment: A sediment deposited by a physical process.
Development: The work done on a mineral property before mineral production begins on a commercial scale.
Development Well: A well drilled within the proven area of an oil or gas reservoir to the depth of the productive stra
Developmental Drilling: Drilling done to delineate the boundaries of a known mineral deposit or to evaluate the deposit in a
Diagenesis: All of the changes which happen to a sediment after deposition, excluding weathering and metamorphis
Diatom: A one celled plant that lives in the shallow waters of lakes, streams or oceans. Many of these secre
Diatom Ooze: A seafloor sediment that consists of at least 30% diatom remains.
Diatomite: A light colored, fine-grained siliceous sedimentary rock that forms from a sediment rich in diatom r
Diatreme: A volcanic vent filled with breccia by the explosive escape of gases.
Differentiated Planet: A planet that has layers composed of elements and minerals of different densities. As an example, Ea
Diorite: A coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende a
Dip: The angle that a rock unit, fault or other rock structure makes with a horizontal plane. Expressed a
Directional Drilling: Drilling wells that are deliberately deviated from the vertical to hit a target that is not directly
Discharge: The volume of water in a flowing stream that passes a given location in a unit of time. Frequently e
Discontinuity: A surface separating rock layers of differing properties or compositions. (See seismic discontinuity
Dissolved Load: The dissolved material being carried by a stream.
Distribution Pipeline: A pipeline that carries natural gas between a main transmission line and a consumer.
Divide: A ridge of high ground separating two drainage basins emptied by different streams.
Dome: An uplift that is round or elliptical in map view with beds dipping away in all directions from a ce
Domestic Operations: Domestic operations are activities located in the United States, including the offshore territorial
Drainage Basin: The geographic area that contributes runoff to a stream. It can be outlined on a topographic map by
Drainage Divide: The boundary between two adjacent drainage basins. Drainage divides are ridge crests (or less obviou
Drawdown: A lowering of the water table around a producing well. The drawdown at any given location will be th
Drift: A general term for all sedimentary materials deposited directly from the ice or melt water of a glac
Drift (Glacial): A collective term for all the rock, sand, and clay that is transported and deposited by a glacier ei
Drilling Arrangement: A contractual agreement under which a mineral rights owner or lessee assigns a fractional interest i
Drumlin: A low, smoothly rounded, elongate hill. Drumlins are deposits of compacted till that are sculpted be
Dry Wash: An intermittent streambed in an arroyo or canyon that carries water only briefly after a rain.
Dry-Hole: A well drilled in hopes of finding oil or natural gas that fails to make commercial production rates
Dry-Hole Contribution: A payment made to the owner of an unsuccessful well in exchange for a log of the well and evaluation
Dune: A mound or ridge of wind-blown sand. Typically found in deserts and inland from a beach. Many dunes
Earthflow: A detached mass of soil that moves downslope over a curved failure surface under the influence of gr
Earthquake: The violent oscillatory motion of the ground caused by the passage of seismic waves radiating from a
Ebb Tide: A tidal current that generally moves seaward and occurs during the part of the tide cycle when sea l
Echo-Sounder: An oceanographic instrument that emits sound pulses into the water and measures its depth by the tim
Ecliptic: The plane that contains the Earth's orbit around the Sun.
Eclogite: An extremely high-pressure metamorphic rock containing garnet and pyroxene.
Ecology: The science of the life cycles, populations, and interactions of various biological species as contr
Effluent Stream: A stream that gains water from ground water flow. These streams are typical of humid climates where
Elastic Limit: The maximum stress that can be applied to a body without resulting in permanent deformation - the ro
Elastic Rebound Theory: A theory that explains the earthquake process. In this theory, slowly accumulating elastic strain bu
Electron: A subatomic particle with a negative charge and of negligible mass that orbits the nucleus of an ato
Elevation: The vertical distance between mean sea level and a point or object on, above or below Earth's surfac
Elliptical Orbit: An orbit with the shape of a geometrical ellipse. All orbits are elliptical or hyperbolic, with the
Eolian: A term used in reference to the wind. Eolian materials or structures are deposited by or created by
Eon: The major divisions of the geologic time scale. Eons are divided into intervals know as 'eras'. Two
Ephemeral Stream: A stream that flows for a short interval of time after precipitation or snow melt in the immediate a
Epicenter: The point on the Earth's surface directly above the focus or hypocenter of an Earthquake.
Epoch: A subdivision of geologic time that is longer than an age but shorter than a period. The Tertiary Pe
Era: A subdivision of geologic time that is longer than a period but shorter than an eon. Precambrian, Pa
Erosion: A general term applied to the wearing away and movement of earth materials by gravity, wind, water a
Esker: A long winding ridge of sorted sands and gravel. Thought to be formed from sediment deposited by a s
Eugeosyncline: The seaward part of a geosyncline: characterized by clastic sediments and volcanism.
Eustatic Change: Sea level changes that affect the whole Earth.
Eustatic Sea Level Change: A rise or fall in sea level that affects the entire earth. Thought to be caused by an increase/decre
Eutrophication: A superabundance of algal life in a body of water: caused by an unusual influx of nitrate, phosphate
Evaporation: The process of liquid water becoming water vapor. Includes vaporization from water surfaces, land su
Evaporite: A chemical sediment or sedimentary rock that has formed by precipitation from evaporating waters. Gy
Evapotranspiration: All methods of water moving from a liquid to water vapor in nature. Includes both evaporation and tr
Exfoliation: A physical weathering process in which sheets of rock are fractured and detached from an outcrop.
Exobiology: The study of life outside the Earth.
Expansive Clay (Expansive Soil): A clay soil that expands when water is added and contracts when it dries out. This volume change whe
Exploration: The work of identifying areas that may contain viable mineral resources. This work can include surfa
Exploratory Drilling: Drilling done to locate mineral deposits in an area where little subsurface data about those mineral
Extinction Angle: The angle between a crystallographic direction, such as a face or cleavage plane, and the direction
Extractive Industries: Industries involved in mineral resource exploration, acquisition, assessment, development or product
Extrusive: Igneous rocks that crystallize at Earth's surface.
Facies: The characteristics of a rock mass that reflect its depositional environment. These characteristics
Farm-Out Arrangement: A contractual agreement in which a mineral rights owner or lessee assigns a working interest to anot
Fault: A planar or gently curved fracture in the Earth's crust across which there has been relative displac
Fault Plane: The plane that best approximates the fracture surface of a fault.
Fault-Block Mountain: A mountain or range formed as a horst when it was elevated between parallel normal faults.
Faunal Succession: A principle of relative dating that is based upon the observed sequence of organisms in the rock rec
Felsic: An adjective used to describe a light-colored igneous rock poor in iron and magnesium content, abund
Fiord: A former glacial valley with steep walls and a U-shaped profile now occupied by the sea.
Fissure: An extensive crack, break, or fracture in the rocks.
Fissure Vein: A cleft or crack in the rock material of the earth's crust, filled with mineral matter different fro
Fjord: A deep, narrow, steep-walled, U-shaped valley that was carved by a glacier and is now occupied by th
Flood: An overflow of water onto lands that are normally above local water levels. Can be caused by stream
Flood Basalt: A sequence of parallel to subparallel basalt flows that were formed during a geologically brief inte
Flood Plain: An area of alluvium-covered, relatively level land along the banks of a stream that is covered with
Flood Stage: A water height that is reached when the discharge of a stream exceeds the capacity of the channel.
Flood Tide: A tidal current that generally moves landward and occurs during the part of the tide cycle when sea
Flow Cleavage: In a metamorphic rock, the parallel arrangement of all planar or linear crystals as a result of rock
Flowing Well: A well that taps an aquifer that is under enough pressure to force water to the surface. Caused when
Fluid Inclusion: A small amount of fluid (liquid and/or gas) trapped within a rock and which is thought to represent
Flume: A laboratory model of stream flow and sedimentation consisting of a rectangular channel filled with
Focus: A point beneath Earth's surface where the vibrations of an earthquake are thought to have originated
Focus (Earthquake): The point at which the rupture occurs: synonymous with hypocenter.
Fold: A planar feature, such as a bedding plane, that has been strongly warped, presumably by deformation.
Foliation: The planar or layered characteristics of metamorphic rocks that are evidence of the pressures and/or
Foraminifer: A group of single-celled organisms, mostly marine, that produce a calcium carbonate shell. Their she
Foraminifera: A class of oceanic protozoa most of which have shells composed of calcite.
Foraminiferal Ooze: A calcareous sediment composed of the shells of dead Foraminifera.
Foreign Operations: Activities located outside of the United States, its offshore territorial waters, commonwealth terri
Formation: The basic unit for the naming of rocks in stratigraphy: a set of rocks that are or once were horizon
Forset Bed: One of the inclined beds found in crossbedding: also an inclined bed deposited on the outer front of
Forset Beds: The distinctly dipping sediment layers deposited on the front of a prograding delta or on the lee si
Fossil: Remains, imprints or traces of an ancient organism that have been preserved in the rock record. Bone
Fossil Fuel: A general term for combustible geologic deposits of carbon in reduced (organic) form and of biologic
Free Oscillation: The ringing or periodic deformation of the whole Earth at characteristic low frequencies after a maj
Friction Breccia: A breccia formed in a fault zone or volcanic pipe by the relative motion of two rock bodies.
Fringing Reef: A coral reef that is directly attached to a landmass not made of coral.
Fumarole: A small vent in the ground from which volcanic gases and heated groundwater emerge, but not lava.
Gabbro: A black, coarse-grained intrusive igneous rock that is the compositional equivalent of basalt. Compo
Gage Height: A measured height of water above a reference datum. Frequently used to describe the height of water
Gaging Station: A facility on a stream, lake, canal, reservoir or other water body where instruments are installed t
Gas Field: The geographic area that is directly above an underground accumulation of natural gas that is commer
Gathering Pipeline: A pipeline that carries natural gas between a production well and a main transmission line.
Gathering System: A network of small pipelines that connect producing wells to the main transmission system.
Geochronology: The science of absolute dating and relative dating of geologic formations and events, primarily thro
Geologic Cycle: The sequence through which rock material passes in going from its sedimentary form, through diastrop
Geomorphic Cycle: An idealized model of erosion wherein a plain is uplifted epeirogenically, then dissected by rapid s
Geomorphology: The science of Earth's landforms, their description, classification, distribution, origin and signif
Geosyncline: A major downwarp in the Earth's crust, usually more than 1000 kilometers in length, in which sedimen
Geotherm: A curving surface within Earth along which the temperature is constant.
Geothermal Gradient: The progressive increase of temperature with depth into the Earth.
Geyser: A hot spring that intermittently erupts a spray of steam and hot water. Caused by the heating of gro
Glacial Rebound: Epeirogenic uplift of the crust that takes place after the retreat of a continental glacier, in resp
Glacial Striations: Grooves and scratches on a bedrock surface that were produced by the movement of a glacier. The orie
Glacial Valley: A valley occupied or formerly occupied by a glacier, typically with a U-shaped profile.
Glacier: A thick mass of ice that forms on land from an accumulation and recrystallization of snow significan
Glacier Surge: A period of unusually rapid movement of one glacier, sometimes lasting more than a year.
Glass: An amorphous (without crystal structure) igneous rock that forms from very rapid cooling of magma. T
Glassiness: The content of extent of glass in an igneous rock.
Gneiss: A coarse-grained, foliated rock produced by regional metamorphism. The mineral grains within gneiss
Graben: A downthrown block between two normal faults of parallel strike but converging dips: hence a tension
Graded Bedding: A rock layer that has a progressive change in particle size from top to bottom. Most common is a seq
Graded Stream: A stream whose smooth profile is unbroken by resistant ledges, lakes, or waterfalls, and which maint
Granite: A coarse-grained, intrusive igneous rock composed primarily of light colored minerals such as quartz
Granitization: The formation of metamorphic granite from other rocks by recrystallization with or without complete
Granular Snow: Snow that has been metamorphosed into small granules of ice.
Granulite: A metamorphic rock with coarse interlocking grains and little or no foliation.
Gravel: The coarsest of alluvial sediments, containing mostly particles larger than 2 mm in size and includi
Gravity Anomaly: The value of gravity left after subtracting from a gravity measurement the reference value based on
Gravity Survey: The measurement of gravity at regularly spaced grid points with repetitions to control instrument dr
Greenhouse Effect: A warming of the atmosphere caused by carbon dioxide and water vapor in the lower portions of the at
Greenschist: A metamorphic schist containing chlorite and epidote (which are green) and formed by low-temperature
Ground Moraine: A glacial deposit of till with no marked relief, interpreted as having been transported at the base
Ground Water: Water that exists below the water table in the zone of saturation. Ground water moves slowly in the
Ground Water Recharge Area: A location where surface water or precipitation can infiltrate into the ground and replenish the wat
Groundwater: The mass of water in the ground below the phreatic zone, occupying the total pore space in the rock
Gully: A small steep-sided valley or erosional channel from 1 meter to about 10 meters across.
Guyot: A flat-topped submerged mountain or seamount found in the ocean.
Gyre: The circular rotation of the waters of each major sea, driven by prevailing winds and the Coriolis e
Half-Life: The time required for half of a homogeneous sample of radioactive material to decay.
Halite: The mineral name for 'rock salt'. A chemical sedimentary rock that forms from the evaporation of oce
Hanging Valley: A tributary to a U-shaped glacial valley which, instead of entering the valley at the same level as
Hard Water: Water that has a significant amount of dissolved calcium and magnesium ions. This water performs poo
Headwater(S): The upper portions of a drainage basin where the tributaries of a stream first begin flow.
Heat Conduction: The transfer of the rapid vibrational energy of atoms and molecules, which constitutes heat energy,
Heat Engine: A device that transfers heat from a place of high temperature to a place of lower temperature and do
Heat Flow: The movement of heat energy from the core of the Earth towards the surface.
Hematite: An iron oxide mineral that is commonly used as an ore of iron. Picture of Hematite.
Hill: A natural land elevation, usually less than 1000 feet above its surroundings, with a rounded outline
Hogback: A formation similar to a Cuesta in that it is a ridge formed by slower erosion of hard strata, but h
Hookes Law: The principle that the stress within a solid is proportional to the strain. It holds only for strain
Hornfels: A high-temperature, low-pressure metamorphic rock of uniform grain size showing no foliation. Usuall
Horst: An elongated block of high topographic relief that is bounded on two sides by steep normal faults. P
Hot Spot: A volcanic center located within a lithospheric plate that is thought to be caused by a plume of hot
Hot Spring: A spring whose waters are above both human body and soil temperature as a result of plutonism at dep
Humus: The dark portion of a soil that consists of organic material that is well enough decayed that the or
Hydration: A chemical reaction, usually in weathering, which adds water or OH to a mineral structure.
Hydraulic Conductivity: A measure of the permeability of a rock or soil: the volume of flow through a unit surface in unit t
Hydrocarbon: Any organic chemical compound (gaseous, liquid or solid) that is composed of carbon and hydrogen. Th
Hydroelectric Power: The production of electrical energy through the use of flowing or falling water.
Hydrograph: A graph that shows the change of a water-related variable over time. Example: A stream discharge hyd
Hydrologic Cycle: The natural cycling of Earth's water between the atmosphere, surface and subsurface through the proc
Hydrology: The science of that part of the hydrologic cycle between rain and return to the sea: the study of wa
Hydrolysis: A chemical reaction involving water that results in the breakdown of mineral material.
Hydrothermal: Pertaining to hot water, the actions of hot water or the products produced by the actions of hot wat
Hydrothermal Activity: Any process involving high-temperature groundwaters, especially the alteration and emplacement of mi
Hydrothermal Deposits: Mineral deposits that are formed by the actions of hot water or gases associated with a magmatic sou
Hydrothermal Metamorphism: Alteration of rock by hot waters or gases associated with a magmatic source.
Hydrothermal Vein: A deposit of minerals precipitated in a fracture by the actions of hot water or gases associated wit
Hypocenter: A point beneath earth's surface where the vibrations of an earthquake are thought to have originated
Hypsometric Diagram: A graph that shows in any way the relative amounts of the Earth's surface at different elevations wi
Igneous Rock: A rock formed by the crystallization of magma or lava. Pictures of Igneous Rocks
Ignimbrite: An igneous rock formed by the lithification of ash flow or pyroclastic flow deposits.
Impermeable Layer: A layer of rock, sediment or soil that does not allow water to pass through. This could be caused by
Inclination: The angle between a line in the Earth's magnetic field and the horizontal plane: also a synonym for
Index Of Refraction: The ratio of the speed of light in a vacuum to the speed in a material: this ratio determines the am
Infiltration: The movement of groundwater or hydrothermal water into rock or soil through joints and pores.
Injection Well: A well that is used to force a fluid into the ground. The injection could be done for disposal or to
Interfacial Angle: The angle between two crystal faces of a crystal, characteristic of a mineral's symmetry.
Interior Drainage: A system of streams that converge in a closed basin and evaporate without reaching the sea.
Intermediate Rock: An igneous rock that has an intermediate silica content. Examples are syenite and diorite. Also see
Intermittent Stream: A stream that goes dry at certain times of the year. Intermittent streams flow during seasons of the
Intermontane Basin: A basin between mountain ranges, often formed over a graben.
Intrusion: A igneous rock body that formed from magma that forced its way into, through or between subsurface r
Intrusive: Igneous rocks that crystallize below Earth's surface.
Intrusive Rock: Igneous rock that is interpreted as a former intrusion from its cross-cutting contacts, chilled marg
Ion: An atom or group of atoms that have gained or lost one or more electron and as a result has an elect
Ionic Bond: A bond formed between atoms by electrostatic attraction between oppositely charged ions.
Iron Formation: A layered deposit of chemical sedimentary rocks containing at least 15 percent (by weight) iron in t
Iron Ore: A chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances) combine
Isograd: A line on a map that represents a specific degree of metamorphism. Rocks on one side of the line hav
Isostasy: A condition of gravitational balance (similar to floating) in which a mass of lighter crustal rocks
Isotope: One of several forms of one element, all having the same number of protons in the nucleus, but diffe
Isotope Geology: The study of the relative abundances of isotopes in rocks to determine their ages (see geo-chronolog
Isotropic Substance: One in which the magnitude of a physical property, such as transmission of light is independent of c
Jade: A translucent gemstone consisting of either jadeite or nephrite that is typically green in color. Ja
Jadeite: A high pressure clinopyroxene that is frequently carved and polished as a gemstone.
Jasper: A variety of colored chert, typically red or green and often found in association with iron ores. Ja
Jet: A variety of coal that is frequently cut and polished for jewelry or ornaments.
Jetty: A human made structure built at right angles to a coastline and extending into the water. Jetties ar
Joint: A large and relatively planar fracture in a rock across which there is no relative displacement of t
Joint Set: A group of joints that are parallel or nearly parallel. They are frequently formed at the same time
Jolly Balance: A spring balance used in the determination of specific gravity.
Juvenile Gas: Gases that come to the surface for the first time from the deep interior.
Juvenile Water: Water that is new to the hydrologic cycle. Brought to Earth's surface through volcanic eruptions.
K-Feldspar: A potassium feldspar such as orthoclase, microcline, sanidine or adularia. Also referred to as potas
Karst: A landscape that is characterized by the features of solution weathering and erosion in the subsurfa
Kerogen: A mixture of organic substances found in many fine-grained sedimentary rocks and a major constituent
Kettle: A small hollow or depression formed in glacial deposits when outwash was deposited around a residual
Kettle Lake: A lake that forms in a kettle.
Kilobar: A unit of pressure equal to 1000 bars (the mean atmospheric pressure at 100 meters above sea level i
Kimberlite: A variety of peridotite that is found in volcanic pipes which are thought to be intrusions from the
Knickpoint: An abrupt change in slope. A point on a stream profile where a change in gradient occurs. This could
Knob: A small hilltop that is round in shape.
Laccolith: An igneous intrusion that has been forced between two layered rock units. The top of the intrusion i
Lahar: A mudflow composed of water and volcanic ash. Lahars can be triggered by the flash melting of the sn
Laminar Flow: A state of uniform flow within a fluid in which the moving particles travel along parallel paths (co
Landslide: The rapid downslope movement of soil and rock material, often lubricated by groundwater, over a basa
Lapilli: Volcanic rock materials which are formed when magma is ejected by a volcano. Typically used for mate
Lateral Moraine: A moraine formed along the side of a valley glacier and composed of rock scraped off or fallen from
Lava: Magma or molten rock that has reached the surface.
Lava Tube: A tunnel below the surface of a solidified lava flow, formed when the exterior portions of the flow
Leaching: The removal of soluble constituents from a rock or soil by moving ground water or hydrothermal fluid
Lease Bonus: Money paid to a mineral rights owner in exchange for granting a lease. This payment may be in additi
Left-Lateral Fault: A fault with horizontal movement. If you are standing on one side of the fault and look across it th
Levee: A long continuous ridge built by people along the banks of a stream to contain the water during time
Limb: One side of a fold. The dipping rock units between the crest of an anticline and the trough of a syn
Limb (Fold): The relatively planar part of a fold or of two adjacent folds (for example, the steeply dipping part
Limestone: A sedimentary rock consisting of at least 50% calcium carbonate (CaCO2) by weight. Picture of Limest
Lineament: A straight topographic feature of regional extent which is thought to represent crustal structure. A
Lineation: Any linear arrangement of features found in a rock.
Liquefied Natural Gas (Lng): Natural gas that has been converted to the liquid state by reducing its temperature. (At standard su
Lithification: The processes through which sediments are converted into sedimentary rock, including compaction and
Lithology: The study and description of rocks, including their mineral composition and texture. Also used in re
Lithosphere: The outer, rigid shell of the Earth, situated above the asthenosphere and containing the crust, cont
Lithospheric Plate: A large slab of the lithosphere that can be moved by convection current motion within the mantle.
Load: The total amount of sediment being carried by a stream or a glacier. Includes suspended materials, d
Lode: A rich accumulation of minerals in solid rock. Frequently in the form of a vein, layer or an area wi
Longitudinal Dune: A long, narrow sand dune that has its long dimension oriented parallel to the direction of the wind.
Longitudinal Profile: A cross section of a stream or valley beginning at the source and continuing to the mouth. These pro
Longshore Current: A current that moves parallel to a shore and is formed from the momentum of breaking waves that appr
Longshore Drift: The movement of sediment along a coastline caused by waves striking the coast at an oblique angle. T
Lopolith: A large laccolith that is bowl-shaped and depressed in the center, possibly by subsidence of an empt
Low-Velocity Zone: A zone within the upper mantle where seismic wave velocities are relatively low. This zone is locate
Lowland: A relatively flat area in the lower levels of regional elevation.
Luster: The general textural impression of a mineral surface, given by the light reflected from it. Terms su
Maar Volcano: A volcanic crater without a cone, believed to have been formed by an explosive eruption of trapped g
Mafic: A term used to describe an igneous rock that has a large percentage of dark-colored minerals such as
Mafic Mineral: A dark-colored mineral rich in iron and magnesium, especially a pyroxene, amphibole, or olivine.
Magma: Molten rock material that forms igneous rocks upon cooling. Magma that reaches the surface is referr
Magma Chamber: A full or emptied magma reservoir in the shallow portion of the lithosphere.
Magmatic Water: Water that is dissolved in a magma or water that is released from a magma. Some magmas can contain u
Magnetic Anomaly: The value of the local magnetic field remaining after the subtraction of the dipole portion of the E
Magnetic Coupling: The transfer of momentum between celestial bodies, especially dust and gas clouds, through magnetic
Magnetic Declination: The horizontal angular difference between True North and Magnetic North.
Magnetic Inclination: The vertical angular difference between a horizontal plane and the orientation of Earth's magnetic f
Magnetic North: The direction that a compass points. The location where Earth's magnetic field dips vertically into
Magnetic North Pole: (1) The point where the Earth's surface intersects the axis of the dipole that best approximates the
Magnetic Reversal: A change in the polarity of Earth's magnetic field in which the north magnetic pole becomes the sout
Magnetic Stratigraphy: The study and correlation of polarity epochs and events in the history of the Earth's magnetic field
Magnetometer: An instrument for measuring either one orthogonal component or the entire intensity of the Earth's m
Magnitude: A measure of earthquake size, determined by taking the common logarithm base 10) of the largest grou
Manganese Nodule: A rounded concretion, rich in manganese minerals with minor concentrations of cobalt, copper and nic
Mantle: The main bulk of the Earth, between the crust and core, ranging from depths of about 40 to 3480 kilo
Mantle Plume: A rising mass of hot mantle material that can create an area of volcanic activity in the center of a
Marble: A non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed
Mass Movement: A downhill movement of soil or fractured rock under the force of gravity.
Mass Spectrometer: An instrument for separating ions of different mass but equal charge (mainly isotopes in geology) an
Mass Wasting: A general term used for any downslope movement of rock, soil, snow or ice under the influence of gra
Massive: A term used in reference to a rock unit that is homogeneous in texture, fabric and appearance.
Massive Rock: A rock that is little or not at all broken by joints, cracks, foliation, or bedding, tending to pres
Maturity: A stage in the geomorphic cycle in which maximum relief and well-developed drainage are both present
Meander: Broad, semicircular curves in a stream that develop as the stream erodes the outer bank of a curve a
Meandering Stream: A stream that has many bends (meanders). This type of drainage pattern usually develops on a nearly
Mechanical Weathering: A general term applied to a variety of weathering processes that result in the particle size reducti
Medial Moraine: A streak of till in the center of a glacier. These are found downslope from the junction of two glac
Medical Geology: The study of human health related to geology. Examples would include the correlation of disease or v
Metamorphism: The changes of mineralogy and texture imposed on a rock by pressure and temperature in the Earth's i
Meteor: A meteoroid that penetrates Earth's atmosphere, producing a streak of bright light caused by inciner
Meteoric Water: Water from the atmosphere, such as rain, snow, hail, or sleet.
Meteorite: A stony or metallic object from inter-planetary space that penetrates the atmosphere to impact on th
Meteoroid: A particle of iron or rock found in inter-planetary space. Distinguished from planets or asteroids b
Micrometeorite: A meteorite less than 1 millimeter in diameter.
Microseism: A weak vibration of the ground that can be detected by seismographs and which is caused by waves, wi
Migmatite: A rock with both igneous and metamorphic characteristics that shows large crystals and laminar flow
Milling: The activities of preparing an ore for market. This can include: crushing, grinding, concentration,
Milling Capacity: The maximum amount of material that a mill can produce in a unit of time.
Mineral: A naturally occurring element or compound with a precise chemical formula and a regular internal lat
Mineral Interest: An ownership, lease, concession, or other contractual interest that gives a party the right to explo
Mineral Lease: A contract in which a mineral interest owner conveys to another party a right to explore for, develo
Mineralogy: The study of minerals - their composition, structure, formation, uses, properties, occurrence and ge
Miogeosyncline: A Geosyncline that is situated near a craton and receives chemical and well-sorted elastic sediments
Mohorovic Discontinuity: The boundary between crust and mantle, marked by a rapid increase in seismic wave velocity to more t
Mohs Hardness Scale: A collection of minerals ranging from very soft to very hard. Use as a comparison scale during miner
Mohs Scale Of Hardness: An empirical, ascending scale of mineral hardness with talc as 1, gypsum 2, calcite 3, fluorite 4, a
Monadnock: An isolated hill or mountain rising above a peneplain.
Monocline: The S-shaped fold connecting two horizontal parts of the same stratum at different elevations. Its c
Moraine: A glacial deposit of till left at the margin of an ice sheet. See specifically by name, ground morai
Mountain: A general term used in reference to an area that is at a conspicuously higher elevation than surroun
Mudflow: A type of mass movement composed mainly of clay-size materials with a high enough water content that
Mudstone: A sedimentary rock composed of clay-size particles but lacking the stratified structure that is char
Multiple Completion Well: A well equipped to produce oil and/or gas from more than one reservoir.
Mylonite: A brecciated metamorphic rock frequently found in a fault zone. The fractured texture is thought to
Nannofossils: A generic term used in reference to very small fossils that are at the limit of resolution by a ligh
Nappe: A large slab of earth's surface that has been moved in a horizontal or near horizontal direction ove
Native Metal: A natural deposit of a metallic element in pure metallic form, neither oxidized nor combined with su
Natural Bridge: An arch-shaped rock formation produced by weathering and/or erosion.
Natural Gas: Naturally occurring hydrocarbons that exist in subsurface rock units in the gaseous state. Methane i
Natural Levee: A mound of sediment that parallels a stream channel forming a levee-like deposit. When flood waters
Natural Reservoir Pressure: The pressure within an oil or gas reservoir that forces oil or gas up the well bore when the reservo
Neap Tide: A tide cycle of unusually small amplitude, which occurs twice monthly when the lunar and solar tides
Neap Tide: A daily tidal range of minimal amplitude that occurs when the moon and sun are positioned at 90 degr
Nebula: An immense, diffuse body of interstellar gas and dust that has not condensed into a star.
Nebular Hypothesis: A theory of the formation of the planets that states that a rotating nebula contracted and was then
Neutron: A subatomic particle, contained in the nucleus of an atom. It has no electrical charge and a mass si
Neutron-Activation Analysis: A method of identifying isotopes of an element by bombarding them with neutrons and observing the ch
Nodule: A mineral mass that has a different composition or is more weathering resistant than its surrounding
Non-Operating Interest: A mineral lease interest that does not involve the rights and responsibilities of exploration, devel
Non-Point Source Pollution: Pollution that does not originate at a single location. In an urban area runoff water can be pollute
Non-Producing: A term that refers to a property, a well or a mine from which commercial amounts of a mineral resour
Normal Fault: A fault with vertical movement and an inclined fault plane. The block above the fault has moved down
Nuclear Electric Power (Nuclear Power): The generation of electricity using the heat released from a nuclear fuel.
Nuclear Fuel: Fissionable materials that are rich enough to sustain a fission chain reaction.
Nuclear Reactor: A facility where a nuclear fission chain reaction can be initiated, controlled, and sustained.
Oblique-Slip Fault: A fault that combines some strike slip motion with some dip-slip motion.
Obsidian: A glassy igneous rock with a composition similar to granite. The glassy texture is a result of cooli
Octahedral Coordination: The packing of six ions around an ion of opposite charge to form an octahedron.
Offshore: The geographic area that is seaward of a coastline.
Oil Field: An underground accumulation of oil and gas concentrated beneath an impermeable trap, preventing its
Oil Shale: A dark-colored shale containing an unusual amount of solid organic material known as kerogen. This s
Old Age: A stage in the development of a landscape when streams have a low gradient and meander back and fort
Oolite: A small sphere of calcium carbonate no more than a few millimeters in diameter and with a concentric
Oolitic: A limestone texture that is characterized by spherical grains of calcium carbonate with a concentric
Opaque: An adjective used in reference to a substance that does not allow light of visible wavelength to ent
Opaque Mineral: A mineral which transmits no light through a thin section under a microscope. Usually a native metal
Ophiolite Suite: The typical sequence of rocks in the oceanic crust from bottom to top: ultrabasic rocks, gabbro, she
Orbit: An elliptical or hyperbolic path traveled by a satellite object around a more massive body. For exam
Ore: A natural deposit in which a valuable metallic element occurs in high enough concentration to make m
Ore Deposit: A natural accumulation of a metal, gemstone or other valuable mineral substance, which is rich enoug
Ore Mineral: A mineral that contains a high enough concentration of a useful element or compound that the element
Original Horizontality: One of the principles of relative dating. Based upon the good assumption that sedimentary rocks are
Orogenic Belt: A linear region, often a former geo-syncline, that has been subjected to folding, and other deformat
Orogeny: The tectonic process in which large areas are folded, thrust-faulted, metamorphosed, and subjected t
Oscillation Ripple: A ripple with a symmetrical cross section and a sharp peak formed by waves.
Oscillation Ripple Marks: Symmetrical ridges in sand or other sediment that are caused by a back-and-forth wave action.
Outcrop: An exposure of bedrock. Outcrops can be formed naturally or by human action. Stream erosion and high
Outfall: A location where water is discharged. Normally used in reference to where a water treatment facility
Outgassing: The release of juvenile gases and water to the surface from a magma source.
Outwash: A glaciofluvial sediment that is deposited by meltwater streams emanating from a glacier.
Overturned Fold: A fold that has both limbs dipping in the same direction, resulting from one of those limbs being ro
Oxbow Lake: A long, broad, crescent-shaped lake formed when a stream abandons a meander and takes a new course.
Oxidation: A chemical reaction in which substances combine with oxygen. For example, the combination of iron wi
Oxidized Element: An element occurring in the more positively charged of two common ionic forms.
P-Wave: Primary seismic waves. The fastest set of earthquake vibrations. They move through the Earth in comp
Pahoehoe: A Hawaiian term for a lava flow that has a surface flow structure appearance that looks like coiled
Paleoclimate: The climate of a given area at a specific time in the past. Paleoclimates can be read from the rocks
Paleocurrent Map: A map that shows the directions of currents at the time of sediment deposition. These directions can
Paleogeographic Map: A map that shows the distribution of sedimentary environments at a specific time in the past. These
Paleomagnetism: The study of Earth's magnetic field over time. When rocks that contain magnetic minerals are deposit
Paleontology: The science of fossils, of ancient life-forms, and their evolution.
Paleowind: A prevailing wind direction in an area, inferred from dune structure or the distribution of volcanic
Pangaea: A large continental landmass that existed from about 300 million years ago through about 200 million
Panthalassa: A hypothetical primeval ocean covering two-thirds of the world except for the continent of Pangaea.
Parent Element: A radioactive element that spontaneously decays into a new substance. The product of this decay is k
Peak Flow: The maximum instantaneous discharge of a stream at a specific location. Corresponds to the highest s
Peat: An accumulation of unconsolidated plant debris that if buried and preserved could become coal. Speci
Pedalfer: A common soil type in humid regions, characterized by an abundance of iron oxides and clay minerals
Pediment: A broad, gently sloping erosional surface of low local relief adjacent to an eroding cliff or mounta
Pedocal: A common soil type of arid regions, characterized by accumulation of calcium carbonate in the A-hori
Pegmatite: A very coarse grained igneous rock, normally of granitic composition. Typically forms during the fin
Pelagic Sediment: A ocean sediment that accumulates far enough from land that detrital materials are a minor component
Peneplain: A hypothetical extensive area of low elevation and relief reduced to near sea level by a long period
Perched Groundwater: An isolated body of ground-water that is perched above and separated from the main water table by an
Perched Water Table: A water table that is isolated from and higher than the regional water table. This can occur when a
Peridotite: A dark-colored, coarse-grained igneous rock that is made up mainly of olivine and pyroxene, with ver
Permeability: A measure of how well a material can transmit water. Materials such as gravel, that transmit water q
Petrochemicals: Organic and inorganic compounds and mixtures that are derived from petroleum. These include: organic
Petroleum: A group of liquid hydrocarbons that includes: crude oil, lease condensate, unfinished oils, refined
Ph: A relative measure of the acidity or alkalinity of a water based upon a scale that ranges between 0
Phreatomagmatic: An explosive volcanic eruption initiated by the interaction of magma and water (usually either meteo
Phyllite: A foliate metamorphic rock that is made up mainly of very fine-grained mica. The surface of phyllite
Physical Weathering: A general term applied to a variety of weathering processes that result in the particle size reducti
Placer Deposit: A mass of stream sediment that contains an economically significant concentration of mineral particl
Plateau Basalt: A sequence of parallel to subparallel basalt flows that were formed during a geologically brief inte
Plinian Eruption: An explosive eruption where large volumes of rock, ash and gas are blasted at high velocity from a v
Point-Source Pollution: Water contamination that can be traced to a single point. A toxic material spill and a sewage discha
Polarity Epoch: An interval of time between reversals of Earth's magnetic field.
Polarity Event: A specific event in the history of Earth's magnetic field. Usually used in reference to a specific p
Polarity Reversal: A change in the polarity of Earth's magnetic field in which the north magnetic pole becomes the sout
Porosity: The volume of pore space in a rock, sediment or soil. Usually expressed as a percentage. This pore s
Potable Water: Water that is agreeable to the taste and not dangerous to the health.
Pothole: A cylindrical or hemispherical hold in the bedrock of a stream that is formed from the continual swi
Pratt Isostatic Compensation: The mechanism in which variations in crustal density act to counterbalance the varying weight of top
Precipitation: Movement of water from the atmosphere to the land or to a surface water body. Rain, hail, snow, dew,
Preferred Orientation: Any deviation from randomness in the distribution of the crystallographic or grain shape axes of min
Primary Recovery: Any crude oil or natural gas that is recovered from a well as a result of the natural pressure withi
Primary Seismic Waves: The fastest set of earthquake vibrations - also known as P-waves. They move through the Earth in com
Prospecting: The activities associated with the search for an area of probable mineralization. It can include: to
Proto-Sun: An intermediate stage in the development of a star in which a large cloud of dust and gases graduall
Proven Reserves: Deposits of fossil fuels whose location and extent are known, as opposed to potential but unproved (
Pumice: A vesicular volcanic glass of granitic composition. It has so many vesicles that it has a very low s
Pyroclastic Flow: A hot, high-velocity mixture of ash, gas and fragmented rock that flows like a liquid down slopes an
Pyroclastic Rock: A rock formed when small particles of magma are blown from the vent of a volcano by escaping gas.
Pyroclastic Texture: The unsorted, angular, and un-rounded texture of the fragments in a pyroclastic rock.
Pyroxene Granulite: A coarse-grained contact metamorphic rock that is formed at high temperatures and low pressures and
Quarry: A surface mine usually for the extraction of construction stone.
Quartz: One of the most abundant minerals in the earth's crust. Has a chemical composition of SiO2 and a har
Quartz Arenite: A sandstone containing very little except pure quartz grains and cement.
Quartzite: (1) A very hard, clean, white metamorphic rock formed from a quartz arenite sandstone. (2) A quartz
Quartzose: An adjective used in reference to a rock that is composted primarily of quartz.
Quartzose Sandstone: (1) A quartz arenite. (2) A clean quartz sandstone, less pure than a quartz arenite, that may contai
Quicksand: A bed of sand that has a high water content. The water within the sand is often flowing through the
Quicksilver: A nickname for the element mercury.
Radial Drainage: A system of streams running in a radial pattern away from the center of a circular elevation, such a
Radiative Transfer: One mechanism for the movement of heat, in which it takes the form of long-wavelength infrared radia
Radiolarian: A group of one-celled marine animals with a siliceous skeleton that occupies shallow portions of the
Radiolarian Ooze: A deep-sea pelagic sediment that contains at least 30% siliceous radiolarian remains.
Radiolarite: The lithified sedimentary rock formed from radiolarian ooze.
Rating Curve: A plot that shows the relationship between the stage and discharge (streamflow) of a specific stream
Ray: A linear landform of the lunar surface emanating from a large crater and extending as much as 100 ki
Reaction Series: A series of interactions between a melt and mineral crystals in contact with the melt. In a reaction
Recharge: Water added to an aquifer or other water body. An aquifer is recharged by precipitation in an area w
Recharge Area: The geographic area where water infiltrates into the ground and enters an aquifer.
Recrystallization: A solid state reaction in which the atoms of existing crystals within a rock are reorganized in resp
Rectangular Drainage: A drainage pattern in which stream channels develop within a large-scale network of intersecting joi
Recumbent Fold: An overturned fold that has two limbs which are nearly horizontal.
Redrilled Well: A previously drilled hole that is reentered and deepened by additional drilling.
Refraction: The bending of a seismic wave as it enters a material of different density, or, the bending of a bea
Refraction (Wave): The departure of a wave from its original direction of travel at the interface with a material of di
Regional Metamorphism: Metamorphism across a broad area caused by the elevated temperatures and pressures of plate collisio
Regolith: A general term used in reference to unconsolidated rock, alluvium or soil material on top of the bed
Regression: A drop in sea level that causes an area of the Earth to be uncovered by seawater, ending marine depo
Relief: Variations in the height and slope of Earth's surface. Also used in reference to the vertical differ
Remote Sensing: The collection of information about an object or area from a distance. Methods employed include phot
Replacement: The dissolving or disintegration of one material followed by precipitation of a new material in its
Replacement Deposit: A deposit of ore minerals by hydrothermal solutions that have first dissolved the original mineral t
Reservoir: A subsurface rock unit that is porous and permeable, and that contains an accumulation of oil and/or
Respiration: The chemical reaction by which carbohydrates are oxidized and by which all animals and plants conver
Retrograde Metamorphism: Mineral changes within a rock that are caused by adjustments to conditions of reduced temperature an
Reverse Fault: A fault with vertical movement and an inclined fault plane. The block above the fault has moved upwa
Reversible Reaction: A chemical reaction which can proceed in either direction, depending on the concentration of reactin
Rheidity: (1) The ability of a substance to yield to viscous flow under large strains. (2) One thousand times
Rhyolite: The fine-grained volcanic or extrusive rocks that are equivalent in composition to granite. Normally
Richter Magnitude Scale: A scale that is used to compare the strength of earthquakes based upon the amount of energy released
Ridge (Mid-Ocean): An elevated area of the sea floor in the center of an ocean basin with rugged topography, a central
Rift Valley: A fault trough formed in a divergence zone or other area of tension.
Right-Lateral Fault: A fault with horizontal movement. If you are standing on one side of the fault and look across it, t
Ring Dike: A dike in the form of a segment of a cone or cylinder, having an arcuare outcrop.
Rip Current: A strong, narrow current of high velocity and short duration that flows seaward through the breaker
Ripple: A very small dune of sand or silt whose long dimension is formed at right angles to the current. Riv
Ripple Marks: A series of parallel or sub-parallel ridges in sand or sediment that is caused by the rhythmic or di
Rock Cycle: The geologic cycle, with emphasis on the rocks produced: sedimentary rocks are metamorphosed to meta
Rock Flour: A glacial sediment of extremely fine (silt-and clay-size) ground rock formed by abrasion of rocks at
Rock Glacier: A mass of rock material, cemented together by ice, that flows down a slope under the force of gravit
Rock Salt: A chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is al
Rockslide: A type of mass wasting in which a large volume of rock debris slides down a slope under the influenc
Rounding: The degree to which the edges and corners of a particle become worn and rounded as a result of abras
Runoff: Liquid water moving over the land surface as a sheet or channelized flow. The portion of precipitati
Rupture Strength: The greatest stress that a material can sustain without fracturing at one atmosphere pressure.
S-Wave: Secondary seismic waves. A seismic wave with a direction of vibration that is perpendicular to the d
Saltation: The transport of sediment in short jumps and bounces above the stream bed or ground by a current tha
Sandblasting: A physical weathering process in which rock is eroded by the impact of sand grains carried by the wi
Sandstone: A detrital sedimentary rock composed of grains from 1/16 to 2 millimeters in diameter, dominated in
Schist: A metamorphic rock containing abundant particles of mica, characterized by strong foliation, and ori
Schistosity: The parallel arrangement of platy or prismatic minerals in a rock that is caused by metamorphism in
Scoria: Congealed lava, usually of mafic composition, with a large number of vesicles formed by gases coming
Sea-Floor Spreading: The mechanism by which new sea floor crust is created at ridges in divergence zones and adjacent pla
Seamount: A mountain on the sea floor that has at least 1000 meters of local relief. Most seamounts are shield
Secular Variation: Slow changes in the orientation of the Earth's magnetic field that appear to be long lasting and int
Sediment: A loose, unconsolidated deposit of weathering debris, chemical precipitates or biological debris tha
Sedimentary Rock: A rock formed by the accumulation and cementation of mineral grains transported by wind, water, or i
Sedimentary Structure: A structure in a sedimentary rock that forms at or near the time of deposition and reveals informati
Sedimentation: The process of deposition of mineral grains or precipitates in beds or other accumulations.
Seepage: The slow movement of water through the pore spaces of a solid material. This term is also applied to
Seif Dune: A large sand dune that forms parallel to the direction of a strong wind that blows in a consistent d
Seismic Discontinuity: A surface within the Earth across which P-wave or S-wave velocities change rapidly, usually by more
Seismic Profile: The data collected from a set of seismographs arranged in a straight line with an artificial seismic
Seismic Refraction: A mode of seismic prospecting in which the seismic profile is examined for waves that have been refr
Seismic Surface Wave: A seismic wave that follows the earth's surface only, with a speed less than that of S-waves. There
Seismic Transition Zone: A seismic discontinuity, found in all parts of the Earth, at which the velocity increases rapidly wi
Seismicity: The study of the worldwide distribution of earthquakes over time and the probability of an earthquak
Service Well: A well drilled to support production from other wells. Some reasons for support wells are: gas injec
Settling Pond: An open pond where waste or process water is allowed to stand while suspended materials settle out.
Shale: a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) wea
Short Ton: A unit of weight that equals 2,000 pounds.
Shut In: A well that is capable of production but which is temporarily closed for repair, cleaning or inacces
Signing Bonus: Money paid to a mineral rights owner in exchange for granting a lease. This payment may be in additi
Siltstone: A clastic sedimentary rock that forms from silt-size (between 1/256 and 1/16 millimeter diameter) we
Sinkhole: A depression in the land surface that results from the collapse or slow settlement of underground vo
Slate: A foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade meta
Solution: A chemical weathering process in which a material is dissolved. Also, the transport of dissolved ion
Storm Sewer: A sewer system that collects surface runoff instead of waste water. These two types of water are kep
Storm Surge: The piling up of water along a shoreline cause by the sustained winds of a strong storm - usually a
Strain: A change in the volume or shape of a rock mass in response to stress.
Stratification: A layered structure of sedimentary rocks in which the individual layers can be traced a considerable
Stratigraphic Sequence: The sequence of sedimentary rock layers found in a specific geographic area, arranged in the order o
Stratigraphy: The science of the description, correlation, and classification of strata in sedimentary rocks, incl
Stratovolcano: A volcanic cone made up of alternating layers of lava flows and pyroclastics. Also known as a compos
Streak: The color of a mineral in powdered form. Streak is normally determined by scraping a specimen across
Streak Plate: A piece of unglazed porcelain that is used for determining the streak of a mineral specimen.
Stream Order: A classification system that represents the relative position of streams in a drainage basin. The hi
Streaming Flow: A tranquil flow slower than shooting flow.
Streamline: A curved line representing the successive positions of a particle in a flow as time passes.
Stress: A force acting upon or within a mass or rock, expressed in terms of unit weight per surface area suc
Striations: Scratches or grooves on a rock or sediment surface caused by abrasive action of objects being transp
Strike: The angle between true North and the horizontal line contained in any planar feature (inclined bed,
Strike-Slip Fault: A fault with horizontal displacement, typically caused by shear stress.
Stromatolite: A fossil form representing the growth habit of an algal mat: concentric spherules, stacked hemispher
Strombolian Eruption: A type of volcanic eruption characterized by fountains of lava jetting from a lava-filled central cr
Subduction Zone: An area at a convergent plate boundary where an oceanic plate is being forced down into the mantle b
Sublimation: The process through which ice goes directly into a vapor without passing through the liquid state.
Submarine Canyon: An underwater canyon, carved into the continental shelf. These can be carved by turbidity currents o
Subsidence: A lowering of the land surface in response to subsurface weathering, collapse or slow settlement of
Supercontinent: A large landmass that forms from the convergence of multiple continents.
Superposed Stream: A stream that cuts across resistant bedrock units. This can occur when the stream's course was deter
Superposition: The concept that the oldest rock layers are at the bottom of a sequence with younger rock layers dep
Supersaturated Solution: A solution that contains more solute than its solubility allows. Such a solution is unstable and pre
Supersaturation: The unstable state of a solution that contains more solute than its solubility allows.
Surf: The breaking or tumbling forward of water waves as they approach the shore.
Surf Zone: An area of breaking waves bounded by the point of first breakers, then landward to the maximum uprus
Surface Wave: A type of seismic wave that travels along Earth's surface.
Suspended Load: The fine sediment kept suspended in a stream because the settling velocity is lower than the upward
Suspension: Transport of sediment by wind or water currents that are strong enough to keep the sediment particle
Swash: The landward rush of water from a breaking wave up the slope of the beach.
Swell: An oceanic water wave with a wavelength on the order of 30 meters or more and a height of perhaps 2
Symbiosis: A relationship between two species who live in close association but do not compete with each other
Syncline: A large fold whose limbs are higher than its center: a fold with the youngest strata in the center.
System: A stratigraphic unit of major significance which was deposited during a specific time period, and wh
System (Stratigraphy): A stratigraphic unit larger than a series, consisting of all the rocks deposited in one period of an
Tableland: A large elevated region with a relatively low relief surface.
Talus: An accumulation of angular rock debris at the base of a cliff or steep slope that was produced by ph
Tar Sand: A sandstone containing the densest asphaltic components of petroleum - the end-product of evaporatio
Tectonics: The study of the movements and deformation of the crust on a large scale, including epeirogeny, meta
Terminal Moraine: A sinuous ridge of unsorted glacial till deposited by a glacier at the line of its farthest advance.
Terrestrial Planet: One of the four rocky planets closest to the sun, which include Mars, Venus, Earth and Mercury.
Terrestrial Sediment: A deposit of sediment that accumulated above sea level in lakes, alluvial fans, floodplains, moraine
Terrigenous Sediment: Sediment that is derived from the weathering of rocks which are exposed above sea level.
Texture: The visible characteristics of a rock which include its grain size, grain orientation, rounding, ang
Texture (Rock): The rock characteristics of grain or crystal size, size variability, rounding or angularity, and pre
Thalweg: A sinuous imaginary line following the deepest part of a stream.
Thermal Conductivity: A measure of a rock's capacity for heat conduction.
Thermal Expansion: The property of increasing in volume as a result of an increase in internal temperature.
Thermal Pollution: Water quality is not defined by chemistry alone. If natural waters are withdrawn for use they should
Thermonuclear Reaction: A reaction in which atomic nuclei fuse into new elements with a large release of heat: especially a
Thermoremnent Magnetization: A permanent magnetization acquired by igneous rocks in the presence of the Earth's magnetic field as
Thrust Fault: A dip-slip fault in which the upper block above the fault plane moves up and over the lower block, s
Tidal Current: A horizontal displacement of ocean water under the gravitational influence of Sun and Moon, causing
Tidal Flat: A broad flat area, very close to sea level that is flooded and drained with each rise and fall of th
Tidal Wave: A term that is incorrectly used in reference to a tsunami. Tsunamis have nothing to do with the tide
Till: An unconsolidated sediment containing all sizes of fragments from clay to boulders deposited by glac
Time Scale: The division of geologic history into eras, periods, and epochs accomplished through stratigraphy an
Topographic Map: A map that shows the change in elevation over a geographic area through the use of contour lines. Th
Topography: The shape of the Earth's surface, above and below sea level: the set of landforms in a region: the d
Topset Bed: A horizontal sedimentary bed formed at the top of a delta and overlying the foreset beds.
Trace Element: An element that appears in minerals in a concentration of less than l percent (often less than 0.001
Trachyte: A fine-grained volcanic rock that contains large amounts of potassium feldspar.
Traction: Transport of sediment by wind or water in which the sediment remains in contact with the ground or b
Transform Fault: A strike-slip fault connecting the ends of an offset in a mid-ocean ridge. Some pairs of plates slid
Transgression: A rise in sea level relative to the land which causes areas to be submerged and marine deposition to
Transition Element: Elements of atomic number 21 to 29, 38 to 46, and 71 to 78, whose second outermost electron shell is
Transmission Pipeline: A pipeline that carries natural gas from a region where it is produced to a region where it is store
Transpiration: The removal of water from the ground into plants, ultimately to be evaporated into the atmosphere by
Transverse Dune: A dune that has its axis transverse to the prevailing winds or to a current. The upwind or upcurrent
Trap: A sedimentary or tectonic structure where oil and/or natural gas has accumulated. These are structur
Trap (Oil): A sedimentary or tectonic structure that impedes the upward movement of oil and gas and allows it to
Travel-Time Curve: A curve on a graph of travel time versus distance for the arrival of seismic waves from distant even
Travertine: Calcium carbonate deposits which form in caves and around hot springs where carbonate-bearing waters
Trellis Drainage: A drainage pattern in which streams intersect at right angles. This forms in areas of long parallel
Trench: A long and narrow deep trough in the sea floor: interpreted as marking the line along which a plate
Trench: A long, narrow, deep depression in the ocean floor that parallels a convergent boundary involving at
Triple Junction: A point that is common to three plates and which must also be the meeting place of three boundary fe
Tsunami: A large sea wave normally produced by sudden movement of the ocean floor caused by an earthquake or
Tuff: A consolidated rock composed of pyroclastic fragments and fine ash. If particles are melted slightly
Turbidite: A vertical sequence of sediments deposited by a turbidity current. Because the largest particles of
Turbidity Current: A mixture of sediment particles and water that flows down the continental slope. These high density
Turbulent Flow: An irregular state of fluid flow in which the particle paths cross one another and may even travel i
U-Shaped Valley: A deep valley with a flat floor and very steep walls. Shaped in cross-section like the letter 'U'. V
Ultrabasic Rock: An igneous rock with a very low silica content and rich in minerals such as hypersthene, augite and
Ultramafic Rock: An igneous rock consisting dominantly of mafic minerals, containing less than 10 percent feldspar. I
Unconformity: A surface that separates two strata. It represents an interval of time in which deposition stopped,
Unconsolidated: A term used when referring to sediment that has not been lithified into a rock. Uncemented.
Unconsolidated Material: Nonlithified sediment that has no mineral cement or matrix binding its grains.
Uniformitarianism: A basic geologic principle. Processes that act upon the Earth today are the same processes that have
Unit Cell: The smallest sample of a substance that has a complete representation of its atomic structure. A cry
Uplift: A structurally high area in Earth's crust. Formed by movements that bend the crust into a structure
Upwelling: Movement of cold water from the floor of a lake or ocean up into a shallow area.
Upwelling Current: The upward movement of cold bottom water in the sea, which occurs when wind or currents displace the
V-Shaped Valley: A valley with a narrow bottom and a cross section shaped like the letter 'V'. Valleys of this shape
Vadose Water: Water that exists in the pore spaces of a rock or soil, between the ground surface and the water tab
Vadose Zone: The region in the ground between the surface and the water table in which pores are not filled with
Valence Electrons: Electrons in the outermost shell of an atom. The electrons that are typically involved in making che
Valley Glacier: A glacier that is smaller than a continental glacier or an icecap, and which flows mainly along well
Van Der Waals Bond: A bond much weaker than the ionic or covalent, which bonds atoms by small electrostatic attraction.
Varve: A thin layer of fine-grained sediment deposited in the still waters of a lake. Varves are frequently
Vector: A mathematical element that has a direction and magnitude, but no fixed position. Examples are force
Vein: A deposit of foreign minerals within a rock fracture or joint.
Ventifact: A rock that exhibits the effects of sand-blasting or 'snowblasting' on its surfaces, which become fi
Vertical Exaggeration: In making sketches of landscapes and cross-sections, the vertical dimension is frequently exaggerate
Vesicle: Spherical or elongated cavities in an igneous rock that are created when a melt crystallizes with bu
Viscosity: The resistance of a fluid to flow. Fluids with a high viscosity resist flow. Fluids with a low visco
Volcanic Ash: A volcanic sediment of rock fragments, usually glass, less than 4 millimeters in diameter that is fo
Volcanic Ash Fall: An accumulation of volcanic ash produced by an eruption. These can be very thick near the vent and d
Volcanic Ash Flow: A mixture of volcanic ash and gases that moves downhill as a density current in the atmosphere.
Volcanic Block: A pyroclastic rock fragment ranging from about fist- to car-sized.
Volcanic Bomb: A projectile of hot magma or rock that is blown from the vent during a volcanic eruption. These soli
Volcanic Breccia: A rock made up of pyroclastic fragments that are at least 64 millimeters in diameter.
Volcanic Cone: A cone-shaped hill or mountain composed of pyroclastic debris and/or lava which builds up around a v
Volcanic Dome: A steep-sided extrusion of very viscous lava that is squeezed from a volcanic vent without major eru
Volcanic Ejecta Blanket: A collective term for all the pyroclastic rocks deposited around a volcano, especially by a volcanic
Volcanic Emanations: Gases, especially steam, emitted from a vent or released from lava.
Volcanic Neck: A vertical intrusion with the geometry of a volcanic pipe. An erosional remant of a volcanic pipe.
Volcanic Pipe: A vertical or nearly vertical tunnel which connects a magma reservoir to the surface. Magma and gas
Volcano: A vent in Earth's surface through which molten rock and gases escape. The term also refers to deposi
Wadi: A stream valley in an arid region that is dry except during the rainy season.
Warping: In tectonics, refers to the gentle, regional bending of the crust, which occurs in epeirogenic movem
Wasting Natural Resources: Mineral resources that can be extracted by people but which can not be readily replaced by the actio
Water Cycle: The movement of water between the atmosphere, ground and surface water bodies through the processes
Water Mass: A mass of water that fills part of an ocean or lake and is distinguished by its uniform physical and
Water Quality: An assessment of the physical, chemical and biological characteristics of water, especially how they
Water Table: A level beneath the Earth's surface, below which all pore spaces are filled with water and above whi
Watershed: The geographic area that contributes runoff to a stream. It can be outlined on a topographic map by
Wave Steepness: The maximum height or amplitude of a wave divided by its wavelength.
Wave-Cut Terrace: A level surface formed by wave erosion of coastal bedrock to the bottom of the turbulent breaker zon
Wavelength: An interval of repetition in a wave-like disturbance. The distance between two successive crests or
Weathering: The set of all processes that decay and break up bedrock, by a combination of physically fracturing
Wellhead Price: The value of natural gas at the mouth of the well.
Withdrawal: A removal of water from a surface or ground water source for use.
Worked Over Well: A previously drilled hole that is reentered and treated to improve or initiate a flow of oil and or
Working Interest: An interest in a mineral property that entitles a party to a share of the mineral production, often
X-Ray Diffraction: A technique used to identify minerals by bombarding them with X-rays. Planes of repetition within th
Xenoblast: A crystal that has grown in a rock during the process of metamorphism and which has not developed it
Xenolith: A preexisting rock that has been incorporated into magma without melting. When the magma crystallize
Xerophyte: A plant that can survive in a very dry location or climate.
Yazoo Stream: A tributary that parallels the main channel for a considerable distance. Joining of these streams is
Yellow Ground: Oxidized kimberlite. A yellow soil that is characteristic of the area above a kimberlite diamond pip
Yield: The quantity of water, coal, gold or other resource that can be produced from a deposit.
Youth: The earliest stage in the development of a landscape. During this stage streams are actively downcut
Youth (Geomorphology): A stage in the geomorphic cycle in which a landscape has just been uplifted and is beginning to be d
Zeolite: A group of hydrous aluminosilicates that are similar to the feldspars. They easily lose and regain t
Zinc Blende: A term used in reference to the mineral sphalerite.
Zirconium: A mineral, zirconium silicate. A hard mineral with a high index of refraction that is used as a gems
Zone Of Aeration: A zone between the land surface and the water table where pore spaces are filled mainly with air. Wa
Zone Of Saturation: The zone beneath the water table where all pore spaces are completely filled with water. Water that
Zone Of Weathering: A subsurface area, above the water table, where mineral and organic materials are subject to weather
Zoned Crystal: A crystal that grew while temperatures were changing or while the composition of the parent solution

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