Glossary of geology terms

Glossary of geology terms

Here is a glossary of Geological terms.


*Abyssal plain- Flat or very gently sloping areas of the deep ocean basin floor.
*Absolute dating- the process of determining a specific date (in years or some other unit of time) for an archaeological, geological or paleontological site or artifact.
*Accrete- Process by which material is added to a tectonic plate.
*Aftershock- Small earthquake that follows a main shock.
*Alkaline- A highly basic substance that dissolve in water.
*Allochthonous- a large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting.
*Alluvial fan- a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
*Alluvium- soil or sediments deposited by a river or other running water.
*Amber- name for fossil resin or tree sap that is appreciated for its colour.
*Andesite- fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals.
*Angular unconformity- an unconformity in which younger strata overlie an erosion surface on tilted of folded layered rock.
*Anticline- an arched fold in which the layers usually dip away from the axis.
*Aquifer- a body of saturated rock or sediment through which water can move readily.
*Aragonite sea- contains aragonite and high-magnesium calcite as the primary inorganic carbonate precipitates.
*Archean Eon- the oldest eon of the earth's history.
*Archipelago- a chain or cluster of islands.
*Asphalt- sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits.
*Asthenosphere- a region of the earth's outer shell beneath the lithosphere. The asthenosphere is of indeterminate thickness and behaves plastically.
*Autochthonous- large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting.


*Banded Iron Formation- distinctive type of rock often found in primordial sedimentary rocks.
*Basalt- fine-grained, mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of clacium-rich plagioclase feldspar.
*Basement rock- the thick foundation of ancient, and oldest metamorphic and igneous rock that forms the crust of continents, often in the form of granite.
*Basin- rock formation scooped out by water erosion.
*Basin and Range Province- particular type of topography that covers much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys.
*Batholith- a large discordant pluton with an outcropping area greater than 100 square kilometers.
*Bedrock- native consolidated rock underlying the surface of a terrestrial planet, usually the Earth.
*Bioerosion- the erosion of hard ocean substrates by living organisms through a number of mechanisms.
*Biostratigraphy- branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.
*Biostratinomy- study of the processes that take place after an organism dies but before its final burial.
*Bioturbation- displacement and mixing of sediment particles by benthic fauna (animals) or flora (plants).
*Blueschist- rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius.
*Brackish- water that has more salinity than fresh water, but not as much as seawater.
*Bowen's reaction series- the sequence in which minerals crystallize from a cooling basaltic magma.


*Calcareous- sediment, sedimentary rock, or soil type which is formed from or contains a high proportion of calcium carbonate in the form of calcite or aragonite.
*Calcite sea- one in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate.
*Caldera- volcanic feature formed by the collapse of land following a volcanic eruption.
*Carbon film- type of fossil, or preservation.
*Carbonate- a salt or ester of carbonic acid.
*Carbonate hardgrounds- surfaces of synsedimentarily-cemented carbonate layers that have been exposed on the seafloor.
*Casting- manufacturing process by which a liquid material such as a suspension of minerals as used in ceramics or molten metal or plastic is introduced into a mould, allowed to solidify within the mould, and then ejected or broken out to make a fabricated part.
*Cenozoic Era- the most recent of the eras; followed the Mesozoic Era.
*Chalk- soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite.
*Chert- fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils.
*Clast- composed of fragments, or clasts, of pre-existing rock.
*Compactions- process by which a newly deposited sediment progressively loses its original water content due to the effects of loading, this forms part of the process of lithification.
*Compression- system of forces that tend to decrease the volume of or shorten rocks.
*Concretion- volume of sedimentary rock in which a mineral cement fills the porosity (i.e. the spaces between the sediment grains).
*Conglomerate- rock consisting of individual stones that have become cemented together.
*Continental crust- layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves.
*Continental margin- zone of the ocean floor that separates the thin oceanic crust from thick continental crust.
*Continental shelf- extended perimeter of each continent and associated coastal plain, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs.
*Convergent boundary- boundary between two plates that are moving toward each other.
*Copal- type of resin produced by plant or tree secretions, particularly identified with the forms of aromatic tree resins used by the cultures of pre-Columbian Mesoamerica as a ceremonially burned incense, as well as for a number of other purposes.
*Coprolites- fossil that results when human or animal dung is fossilized.
*Core- innermost layer(s) of a planet.
*Craton- old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
*Cross-bedding- inclined sedimentary structures in a horizontal unit of rock; such tilted structures indicate the type of depositional environment, not post-depositional deformation.
*Crude oil- a liquid mixture of naturally occurring hydrocarbons.
*Crust- outermost solid shell of a planet or moon.


*Dacite- an igneous, volcanic rock with a high iron content.
*Daughter product- the isotope produced by radioactive decay.
*Delta- landform where the mouth of a river flows into an ocean, sea, desert, estuary, lake or another river.
*Dendrites- crystal that develops with a typical multi-branching tree-like form.
*Deposition- geological process by which material is added to a landform or land mass.
*Detachment fault- major fault in a mountain belt above which rocks have been intensely folded or faulted.
*Diagenesis- chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism.
*Diatomite- naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder.
*Diorite- grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene.
*Dip slope- geological formation often created by erosion of tilted strata.
*Disconformity- a surface that represents missing rock strata but beds above and below that surface are parallel to one another.
*Divergent plate boundary- boundary separating two plates moving away from each other.
*Dolomite- name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg(CO3)2 found in crystals.
*Drill core- drill specifically designed to remove a cylinder of material, much like a hole saw.
*Drumlin- an elongated whale-shaped hill formed by glacial action.


*Eon- the largest unit of geologic time.
*Epicenter- point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or other underground explosion originates.
*Epoch- each period of the standard geologic time scale is divided into epochs (e.g., Pleistocene Epoch of the Quaternary Period).
*Erosion- displacement of solids (sediment, soil, rock and other particles) usually by the agents of currents such as, wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
*Erratic-piece of rock that deviates from the size and type of rock native to the area in which it rests; the name "erratic" is based on the errant location of these boulders.
*Escarpment- transition zone between different physiogeographic provinces that involves an elevation differential, characterized by a cliff or steep slope.
*Esker- long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles in length and, because of their peculiar uniform shape, somewhat resemble railroad embankments.
*Estuary- semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea.
*Evaporite- water-soluble, mineral sediments that result from the evaporation of bodies of surficial water.
*Exfoliation- the stripping of concentric rock slabs from the outer surface of a rock mass.
*Extension- strain involving an increase in length. Extension can cause thinning and faulting.
*Extrusive- mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.


*Fault- planar rock fracture, which shows evidence of relative movement.
*Feldspars- group of most common minerals of the earth's crust. All feldspars contain silicon, aluminum, and oxygen and may contain potassium, calcium and sodium.
*Felsic- silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.
*Ferromagnesian mineral- iron/magnesium bearing mineral, such as augite, hornblende, olivine or biotite.
*Fold- stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of plastic (i.e. permanent) deformation.
*Foliation- parallel alignment of textural and structural features of a rock.
*Fossil- mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms.
*Freezing- process whereby a liquid turns to a solid when cold enough.


*Gabbro- dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt.
*Gastroliths- rocks, which are or have been held inside the digestive tract of an animal.
*Geologic maps- special-purpose map made to show geological features.
*Glass- hard, brittle, transparent solid, such as used for windows, many bottles, or eyewear, including soda-lime glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride.
*Gondwanaland- the southern part of Pangaea that formed South America, Africa, India, Australia and Antarctica.
*Granite- common and widely occurring type of intrusive, felsic, igneous rock.
*Granodiorite- intrusive igneous rock similar to granite, but contains more plagioclase than potassium feldspar.
*Graywacke- variety of sandstone generally characterized by its hardness, dark color, and poorly-sorted, angular grains of quartz, feldspar, and small rock fragments set in a compact, clay-fine matrix.


*Half-life- the time it takes for a given amount of a radioactive isotope to be reduced by one-half.
*Hot springs- spring that is produced by the emergence of geothermally-heated groundwater from the earth's crust.
*Hydrothermal vent- fissure in a planet's surface from which geothermally heated water issues.
*Hypersaline- saltiness or dissolved salt content of a body of water.


*Ichnology- branch of biology that deals with traces of organismal behavior.
*Igneous rock- rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
*Interbedded- beds (layers) of rock lying between or alternating with beds of a different kind of rock.
*Intrusion- body of igneous rock that has crystallized from molten magma below the surface of the Earth.
*Island arc- chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.
*Isotope- different forms of an element each having different atomic mass (mass number).


*Jurassic- major unit of the geologic timescale that extends from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, the end of the Triassic to the beginning of the Cretaceous.


*Kame- geological feature, an irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier, and is then deposited on the land surface with further melting of the glacier.
*Karst- landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite.
*Kettle- fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash.


* Lava- molten rock expelled by a volcano during an eruption.
* Limestone- sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3).
* Loess- fine, silty, pale yellow or buff in color, windblown (eolian) type of unconsolidated deposit.
* Lowland- broad expanse of land with a general low level.


*Mafic- a silicate mineral or rock that is rich in magnesium and iron.
*Magma- molten rock that sometimes forms beneath the surface of the earth (or any other terrestrial planet) that often collects in a magma chamber.
*Mantle- highly viscous layer directly under the crust, and above the outer core.
*Marine terrace- narrow flat area often seen at the base of a sea cliff caused by the action of the waves.
*Marl- calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite.
*Mélange- large scale breccia formed in the accretionary wedge above a subduction zone.
*Metamorphism- the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i.e without melting.
*Micropaleontology- branch of paleontology which studies microfossils.
*Mid-oceanic ridges- underwater mountain range, typically having a valley known as a rift running along its axis, formed by plate tectonics.
*Mineralization- hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".
*Molding- process of manufacturing by shaping pliable raw material using a rigid frame or model called a mold.
*Moraine- glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age.

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