Geological Glossary - C

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
C-horizon	The lowest layer of soil, consisting of fragments of rock and their chemically weathered products.
CSAMT	Controled Source Audio-MagnetoTelluric method in which an artificial source generally a long cable is used to simulate the audio-frequency magnetotelluric fields.
Cambrian	A period in the geologic time scale that spans from 570 to 505 million years ago.
Catastrophism	The doctrine that sudden violent and widespread events caused by supernatural forces formed most of the rocks that are visible at the earth's surface.
Cenozoic	An era in geologic time that spans from 65 million years ago to the present.
Cordilleran ice sheet	Ice cap that grew in western North America during the Pleistocene Epoch. It began growing first in Canada, eventually covering much of British Columbia, Alaska, the northern U.S., and parts of several western states.
Cretaceous	A period in the geologic time scale that spans from 144 to 65 million years ago.
Curie temperature	Temperature above which there is no spontaneous magnetization.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
calcareous	A descriptive term used for rocks and other earth materials that have an abundance of calcium carbonate (CaCO3). For example, a calcareous sandstone has up to 50% calcium carbonate.
calcic horizon	In regions that receive about 1.3 m of rain or less, calcium carbonate will often accumulate in the lower portion of a soil profile. In fine-grained soils, such as under the prairies of the mid-western United States, the carbonate often takes the form of discrete nodules up to several centimeters in diameter. In gravelly soils such as are common in the western U.S., carbonate will begin by coating clast, and with time it will entirely plug soil voids, forming what is commonly called a caliche or more formally a calcic horizon.
calcite	Mineral made of calcium carbonate (CaCO3). Generally white, easily scratched with knife. Most seashells are made of calcite or related mineral. This is the lime of limestone.
calcrete	A surficial gravel and sand conglomerate cemented by calcium carbonate.
caldera	"From the Spanish for cauldron. A basin-shaped volcanic depression; by definition, at least a mile in diameter. Such large depressions are typically formed by the subsidence of volcanoes. Crater Lake occupies the best-known caldera in the Cascades. "
caliche	Nodular calcium carbonate (opaque reddish-brown-to-white) that accumulates in the B-horizon ot soil in warm climates that are dry part of the year. Also called calcrete.
carbonaceous chondrite	A stony meteorite that contains carbon compounds.
carbonate	A sedimentary rock made mainly of calcium carbonate (CaCO3). Limestone and dolomite are common carbonate sedimentary rocks.
carbonate ion	The anion group CO3 with a charge of minus two.
carbonate mineral	A mineral in which the basic building block is a carbon atom linked to three oxygen atoms. Calcite, aragonite and dolomite are the most abundant examples found in sediment and sedimentary rocks.
carbonate platform	A submarine or intertidal shelf whose elevation is maintained by active shallow water carbonate deposition.
carbonate rock	A sedimentary rock that consists primarily of carbonate mineral. The dominant mineral is nearly always either calcite, in which case the rock is limestone, or dolomite, in which case the rock is dolomite.
carbonate rocks	General term for limestone and dolostone.
carbonate sediment	Unconsolidated sediment that consisls primarily of carbonate mineral, usually aragonite or calcite.
carbonic acid	A mild acid formed when water and carbon dioxide chemically combine in the atmosphere and soil.This acid is a very important component in the development of cave decorations (speleothems)
carbonization	The mode of fossilization in which liquid and gases escape, leaving a residue of carbon on the surface of an impression of the organism.
cataclastic rock	Metamorphic rocks that resemble breccia or poorly sorted sandstone and that form by dynamic metamorphism, which breaks and reorients grain.
catena	Sequence of proximately located soil of about the same age and derived from similar parent material but having different characteristics due to variation in relief and/or drainage.
cation	Any ion with a positive electric charge.
cation exchange capacity	Sum total of exchangeable cation retained by negatively charged soil particles. Units of milliequivalents per 100 grams of soil. Abbreviated CEC.
cave	A natural opening in the ground extending beyond the zone of light and large enough to permit the entry of an average human
cave system	A cave or caves having a complex network of interconnected chambers and passages that constitute an underground drainage system
cementation	The lithification of sediment by the precipitation of mineral from watery solutions percolating through the sediment.
central angle	An angle with the vertex at the center of the Earth with one ray passing through the hypocenter (and also the epicenter) and the other ray passing through the recording station.
central vent	The largest vent of a volcano, situated at the center of its cone.
chemical remanent magnetization	Magnetization acquired isothermally through chemical change at temperatures below the Curie temperature either by grain growth or by alteration of a magnetic parent to a magnetic daaghter.
chemical sediment	A sediment created by precipitation of one or more mineral from natural waters.
chemical sedimentary rock	Sedimentary rock composed of mineral that were precipitated from water. This process begins when water traveling through rock dissolves some of the minerals, carrying them away from their source. Eventually these minerals are redeposited, or precipitated, when the water evaporates away or when the water becomes over-saturated.
chemical weathering	The total set of all chemical reactions that act on rock exposed to water and atmosphere and so change it mineral to stable form.
chert	An impure rock, often gray in color, that consists primarily of extremely small quartz crystal precipitated from water solutions.
chlorite	Family of platy silicate mineral containing various amounts of magnesium, iron, aluminum, water, and small amounts of other elements. Some mineralogists include chorites in the mica family because the crystal form small flakes. Commonly green.
chloroplast	A body within a plant cell or plantlike cell that serves as the site of photosynthesis within the cell. Chloroplasts are apparently evolutionary descendants of blue-green algae that became trapped in other single-celled organisms.
chondrite	A stony meteorite having chondules and composed almost entirely of the silicate minerale olivine, pyroxene, plagioclase which are the most abundant constituents of the earth's crust. The age of chondrictic meteorites uniformly falls close to 4.6 billion years, nearly as great as the solar system itself. The chonditric meteorites may be close in composition to the terrestiae planets beforc they formed a core.
cinder	A bubbly (vesicular) volcanic rock fragment that form when molten, gas-filled lava is thrown into the air, then solidifies as it falls.
cinder cone	A steep, conical hill built up about a volcanic vent and composed of coarse pyroclasts expelled from the vent by escaping gases.
circumpolar current	The circular flow of water around Antarctica resulting from the juncture of the west-wind drifls of the Atlantic Pacific and Indian Oceans.
cirque	The head of a glacial valley, usually with the form of one half of an inverted cone. The upper edges have the steepest slope, approaching vertical, and the base may be flat or hollowed out and occupied by a small lake or pond.
clast	A solid product of erosion. Clasts are sometimes referred to as detritus or detrital material.
clastic	Pertaining to a rock or sediment composed principally of fragmental detrital materials.
clastic rock	A sedimentary rock formed from mineral particles (clasts) that were mechanically transported.
clay	"Any of a number of hydrous aluminosilicate mineral formed by weathering and hydration of other silicates; also, any mineral fragment smaller than 1/255 mm."
clay minerals	"Clay mineral are a group of complex and loosely-defined minerals containing aluminum and silica; they form from the alteration and weathering of primary silicate minerals"
clay-sized sediment	Sediment in which particles are smaller than 1/256 millimeter. Most sediment of this size belongs to the clay mineral family.
claystone	A sedimentary rock that consists primarily of clay but that is not fissile like shale.
cleavage	The tendency of a mineral to break along weak planes.
closed hydrochemical system	Physical portion of the earth in which the mass of a given immobile chemical element remains constant throughout a chemical and physical transformation process and is enriched only by removal of mobile elements.
coal	A metamorphic rock formed from stratified plant remains. It contains more than 50 percent carbon and burns readily.
coast	The part of land that is in contact with a large body of water and effected by the action of the wave.
coastal plain	A low plain of little relief adjacent to the ocean and covered with gently dipping sediment.
cobble	A piece of gravel between 8 and 256 millimeters in size.
coccolith	One of the many armorlike plate that surround single-celled marine algae known as coccolithophores.
cogenetic (comagmatic)	Igneous rocks related by differenntiation to a common parental source.
compaction	Occurs when the weight of overlying material compresses more deeply buried sediment. Along with cementation, this process converts sediments to solid rock.
components principle	The principle stating that a body of rock is younger than any other body of rock from which any of its components are derived.
composite cone	The volcanic cone of a stratovolcano, composed of both cinder and lava flows.
composite volcano	A steep volcanic cone built by both lava flows and pyroclastic eruption.
compositional maturity	"Extent to which a clastic sediment approaches the compositional end product of chemical weathering; the extent to which the most stable components of a sediment have been enriched over unstable components. In sandstone, compositional maturity can be conveniently expressed in terms of the abundance of quartz the most stable common phase in most sandstones."
concretion	A hard nodular structure formed in sediment or in a sedimentary rock by diagenesis.
condensation	The change of state of water from the vapor to the liquid phase. Results in liberation of 80 calories per cubic centimeter.
conduction	Transfer of heat from one place to another by molecular agitation and without movement of the medium.
conformable	Rock layer that were deposited in sequence without episodes of erosion between deposition of layers. .
conglomerate	A rock consisting of rounded clast of gravel surrounded by sand.
connate water	Water included in the groundwater which is derived from the rock itself, as opposed to water which has percolated down from the surface.
contact metamorphism	Mineralogical and textural changes and deformation of rock resulting from the head and pressure of an igneous intrusion in the near vicinity.
continent	A large landmass covered with lighter (less dense) rocks. Since their rocks weigh less than the denser oceanic crust, continent float higher on the mantle and overide oceanic plate on colision.
continental accretion	The marginal growth of a continent along a subduction zone by mountain building or by addition of a microplate.
continental collision	Convergence of two continental plate. Such a convergence between the Indian and Eurasian plates is responsible for producing the Himalayas.
continental crust	The layer of the Earth that lies under continent and the continental shelves. It ranges in thickness from 35 to 60 km. Its upper layer has a density of ~2.7 g/cm3 and is composed of rocks that are rich in silica and alumina. The average elevation of the Earth's continental crust is 0.84 km above sea level.
continental drift	The theory that horizontal movement of the earth's surface causes slow relative movements of the continent toward or away from one another.
continental margin	The submarine edge of the continental shelf, from which the continental slope descends. In the modern world this margin generally lies about 200 meters (~600 feet) below sea level.
continental margin	a. The zone separating the emergent continent from the deep sea bottom. It generally consists of the continental shelf, the continental slope, and the continental rise.
continental rise	A more gently sloping region along the base of the continental slope. The continental rise is a depositional feature formed of sediment transported down the slope often by turbidity current.
continental rise	The submarine surface beyond the base of the continental slope, generally having a gradient of less than 1:1,000, occurring at depths from 4,500 to 17,000 ft (1.37 to 5.18 km), and leading down to abyssal plain
continental shelf	a. The gently sloping tread around a continent, extending from the low-water line to the depth of approx. 100 fathoms (183 m), at which depth there is a marked increase of slope toward the great depths. b. The submerged prolongation of the land mass of the coastal state, consisting of the seabed and subsoil of the shelf, the slope, and the rise.
continental shelf	That part of the continent that is covered by water. Continental shelves are more than 322 km wide and about 122 m deep. At the edges of the shelves the continental slope drop rapidly from 100 to 200 m to 3000 to 3700 m.
continental shield	A surface of low relief, within a few hundred meters above sea level, who's only features of relief are due to resistant rocks rising 50 to 100 m above their surroundings.
continental slope	a. The declivity from the offshore border of the continental shelf at depths of approx. 100 fathoms (600 ft or 183 m) to oceanic depths. It is characterized by a marked increase in gradient.
convection	Rotational flow of a fluid resulting from imbalances in density. This often occurs because the fluid below is heated and becomes less dense than the fluid above or because the fluid above is cooled and becomes more dense than the fluid below.
convergent plate boundary	A boundary in which two plate collide. The collision can be between two continent (continental collision), an relatively dense oceanic plate and a more buoyant continental plate (subduction zone) or two oceanic plates (subduction zone).
core	The innermost layer of the Earth. The inner core is solid and has a radius of about 1300 kilometers. (The radius of the Earth is about 6371 kilometers.) The outer core is fluid and is about 2300 kilometers thick. S-waves cannot travel through the outer core.
cosmogenic isotope	Isotope produced by nuclear reactions induced by cosmic-ray particles.
cotectic	Line curve or surface on a phase diagram depicting crystal-melt equilibria along which two crytals co-precipitate.
crater	A steep-sided usually circular depression formed by either explosion or collapse at a volcanic vent or surface impact of a meteorite, asteroid, or comet.
craton	The relatively stable nucleus of a continent. Cratons are made up of a shield-like core of Precambrian Rock and a buried extension of the shield
craton	A part of the Earth's crust that has attained stability, and has been little deformed for a prolonged period. The term is now restricted to the extensive central areas of the continent
crevasse	A deep crack in a glacier caused by the stresses of the ice's movement.
cross section, geologic	A cross-section is a drawing representing a portion of the Earth in a vertical plane.
crust	"The outermost layer or shell of the Earth, defined according to various criteria, including seismic velocity, density and composition; that part of the Earth above the Mohorovicic discontinuity, made up of the sial, or the sial and the sima. It represents less than 0.1% of the Earth's total volume. Crustal thickness is approximately 50 km and outer radius is approximately 6371 km."
crust	The outermost rock hell. Outer part of the earth composed essentially of crystalline rocks. Crustal thickness is approximately 50 km and outer radius is approximately 6371 km.
crystallization	Growth of mineral (crystalline solid) from a liquid or gas
cuesta	A long, narrow hill with a steep slope on one side ant a gentle slope on the other.