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Iowa State University - Geology terms Category: Education > University Date & country: 18/11/2013, USA Words: 782

cataclastic metamorphism
Takes place in an environment where intense pressure due to shearing is common, as in a major fault zone.

cation
An ion that has a positive electrical charge. That is, an atom that has lost one or more electrons.

cave
A natural open space underground, large enough for a person to enter. Most commonly occur by the dissolution of soluble rocks, generally limestone.

cementation
Process by which a binding, or cementing, agent is precipitated in spaces among individual particles of a deposit. Common cementing agents are calcite, quartz, and dolomite.

Cenozoic
The current geologic era, which began 66.4 million years ago and continues to the present.

chain reaction
A self-sustaining nuclear reaction, made possible when neutrons released by fission of some atoms in a nuclear reactor strike other atoms, causing them to fission as well.

chalcedony
. Occurs in limestone, dolostone, and mudstones.

chalcedony
A cryptocrystalline form of quartz, microscopically fibrous with waxy luster. May be transparent or translucent, and with a uniform tint of white, gray, pale blue, and, less often, black.

chalk
A variety of limestone made up in part of biochemically derived calcite, in form of skeletons or skeletal fragments of microscopic oceanic plants and animals mixed with fine-grained calcite deposits of biochemical or inorganic-chemical origin.

chemical bond
The interactions among the electrons of atoms that hold atoms together to form chemical compounds. If electrons cluster primarily around one atom of a pair, the bond is ionic . If they are shared more or less equally, it is covalent . If electrons move freely between atoms over an extended region, the bond is metallic. A weak electrostatic bond due...

chemical remanent magnetism
Acquired as magnetic minerals form and align themselves to the global magnetic field during diagenesis of a sedimentary deposit.

chemical sediment
Sediment formed by chemical precipitation from water. Example: halite precipitated as the result of the evaporation of sea water.

chemical weathering
see decomposition

chert
A cryptocrystalline form of quartz, microscopically granular. Occurs as nodules and as thin, continuous layers. Duller, less waxy luster than

chlorofluorocarbons
(CFC) Gases that can be dissociated by solar radiation, which releases chlorine, which in turn destroys ozone.

cinder cone
A conical volcano formed by the accumulation of pyroclastic debris around a vent.

cirque
A steep-walled hollow in a mountain side, shaped like an amphitheater, or bowl, with one side partially cut away. Place of origin of a mountain glacier.

clastic
Refers to rock or sediments made up primarily of broken fragments of pre-existing rocks or minerals.

clay 1
. The name for a family of finely-crystalline sheet silicate minerals. 2. Fine-grained soil consisting of mineral particles, not necessarily clay minerals, that are less than 0.074 mm in their maximum dimension.

claypan
A layer of stiff, compact, relatively impervious clay which is not cemented. compare caliche , fragipan, hardpan.

cleavage
1. of a mineral: The tendency of a mineral to split along planes determined by the crystal structure. 2. of a rock: see slaty cleavage

coal
Sedimentary rock composed of combustible matter derived from the partial decomposition of plant material.

coast
A narrow strip of land along the margin of the ocean extending inland for a variable distance from low water mark.

col
Mountain pass formed by enlargement of two opposing cirques until their head walls meet and are broken down.

column
Pillar formed as a stalactite and stalagmite meet.

columnar jointing
The type of jointing that breaks rock, typically basalt, into columnar prisms. Usually the joints form a more or less distinct hexagonal pattern.

compaction
Reduction of pore space between individual particles as the result of overlying sediments or of tectonic movements.

competence
The maximum size of particle that a stream can carry.

composite
volcano see stratovolcano

compression
Squeezing a material from opposite directions.

concordant
Lying parallel to, rather than cutting across surrounding strata.

concretion
A compact mass of mineral matter, usually spherical or disk-like in shape and embedded in a host rock of different composition. They form by precipitation of mineral matter about a nucleus such as a leaf, or a piece of shell of bone.

conduction
Heat transport by direct transfer of energy from one particle to another, without moving the particle to a new location. compare convection , radiation .

cone of depression
A downward distortion or dimple in the water table that forms as a well pumps water faster than it can flow through the aquifer.

conglomerate
A clastic sedimentary rock composed of lithified beds of rounded gravel mixed with sand.

Constancy of Interfacial Angles
The statement that the angles between congruent crystal faces on samples of a single mineral are always identical. A consequence of, and therefore evidence for the existence of crystalline structure in minerals.

contact metamorphism
Metamorphism genetically related to the intrusion (or extrusion) of magmas and taking place in rocks at or near their contact with a body of igneous rock.

continental
ice glacier An ice sheet that obscures all but the highest peaks of a large part of a continent.

continental arc
A belt of volcanic mountains on the continental mainland that lie above a subduction zone. compare island arc .

continental crus
t The part of the crust that directly underlies the continents and continental shelves. Averages about 35 km in thickness, but may be over 70 km thick under largest mountain ranges.

continental deserts
Located in continental interior far from moisture-bearing winds.

continental divide
A major drainage divide separating the drainage to one ocean from another.

continental rise
The portion of the continental margin that lies between the abyssal plain and the continental slope. The continental rise is underlain by crustal rocks of the ocean basin.

continental shelf
The portion of the continental margin that extends as a gently sloping surface from the shoreline seaward to a marked change in slope at the top of the continental slope . Seaward depth averages about 130 m.

continental slope
That part of the continental margin that lies between the continental shelf and the continental rise. Slope relatively steep, 3o

convection
Heat transport by moving particles, and the thermal energy that they carry, to a new location. compare conduction , radiation .

convection cell
A cyclical pattern of movement in a fluid body such as the ocean, the atmosphere, or the Earth

convergent boundary
A boundary between two plates of the Earth

co-product
A mineral commodity that is recovered from a mining operation for some other mineral product. Example: Platinum is commonly a co-product of nickel mining.

coquina
A coarse-grained, porous variety of clastic limestone made up chiefly of shells and shell fragments.

core
Innermost zone of Earth. Consists of two parts, an outer liquid section and an inner solid section, both chiefly of iron and nickel with about 10 percent lighter elements. It is surrounded by the mantle.

correlation
Process of establishing contemporaneity of rocks or events in one area with rocks or events in another area.

crater
1. A steep-walled, usually conical depression at the summit or on the flanks of a volcano, resulting from the explosive ejection of material from a vent. 2. A bowl-shaped depression with a raised, overturned rim produced by the impact of a meteorite or other energetic projectile.

craton
The stable portions of the continents that have escaped orogenic activity for the last 2 billion years. Made predominantly of granite and metamorphic rocks. compare orogen .

creep
1. The very slow, generally continuous downslope movement of soil and debris under the influence of gravity. 2. The movement of sand grains along the land surface.

crevasse
1. Breach in a natural levee . 2. Deep crevice or open fracture in glacier ice.

cross-bedding
see inclined bedding .

cross-cutting relationships
Geologic discontinuities that suggest relative ages: A geologic feature is younger than the feature it cuts. Thus, a fault cutting across a rock is younger than the rock.

crust
The upper part of the lithosphere , divided into oceanic crust and continental crust .

crystal
The multi-sided form of a mineral, bounded by planar growth surfaces, that is the outward expression of the ordered arrangement of atoms within it.

crystal settling
Gravitational sinking of crystals from the liquid in which they formed, by virtue of their greater density. A type of igneous differentiation.

crystal structure
The regular and repeated three-dimensional arrangement of atoms or ions in a crystal.

cumulate
An igneous rock that forms by crystal settling .

Curie point
The temperature above which a mineral loses its magnetism.

current ripple mark
An asymmetric ripple mark formed by wind or water moving generally in one direction. Steep face of ripple faces in direction of current. compare oscillation ripple mark .

cyclothem
A series of beds, of interest because they include coal, which were associated with unstable shelf or interior basin conditions in which alternating marine transgressions and regressions occurred.

Darcy
A formula describing the flow of water through an aquifer.

daughter
An atom that results from the radioactive decay of a parent atom.

debris flow
Fast-moving, turbulent mass movement with a high content of both water and rock debris. The more rapid debris flows rival the speed of rock slides.

decay rate
The rate at which a population of radioactive atoms decays into stable daughter atoms. Rate often expressed in terms of half life of the parent isotope .

decomposition
(chemical weathering) Weathering processes that are the result of chemical reactions. Example: the transformation of orthoclase to kaolinite.

deflation
A process of erosion in which wind carries off particles of dust and sand.

dehydration
Any process by which water bound within a solid material is released. Example: Gypsum (CaSO4

dendritic drainage
A stream pattern that, when viewed on a map or from the air, resembles the branching pattern of a deciduous tree such as a maple or oak.

denudation
The sum of the processes that result in the wearing away or the progressive lowering of the Earth

depositional environment
The nature of the environment in which sediments are laid down. They are immensely varied and may range from the deep ocean to the coral reef and the glacial lake of the high mountains. The nature of the depositional environment may be deduced from the nature of the sediments and rock deposited there.

depositional remanent magnetism
Develops as magnetic minerals settle through water and align themselves in the Earth

desert pavement
A lag accumulation of pebbles or boulders that cuts off further deflation.

desertification
A process of land degradation initiated by human activity, particularly in the zones along the margins of deserts.

detrital sedimentary rock
A sedimentary rock made up of detrital sediments.

detrital sediments
Sediments made of fragments or mineral grains weathered from pre-existing rocks.

diagenesis
All the physical, chemical, and biologic changes undergone by sediments from the time of their initial deposition, through their conversion to solid rock, and subsequently to the brink of metamorphism.

differential weathering
Weathering that occurs at different rates, as the result of variations in composition and mechanical resistance of rocks, or differences in the intensity of weathering processes.

differentiation
The process of developing more than one rock type, in situ, from a common magma.

dike
A tabular igneous intrusion that cuts across the surrounding rock.

dilatancy
An increase in the bulk volume of rock during deformation. Possibly related to the migration of water into microfractures or pores.

dip
The angle that a structural surface such as a bedding plane or fault surface makes with the horizontal, measured perpendicular to the strike and in the vertical plane.

dip pole
see magnetic pole

dip slip fault
A fault on which the movement is parallel to the dip of the fault plane.

directed pressure
Pressure applied predominately in one direction, rather than uniformly.

discharge
In a stream, the volume of water passing through a channel in a given time.

disconformity
An unconformity in which the beds above the unconformity are parallel to the beds below the unconformity.

discordant
Cutting across surrounding strata.

disintegration
(mechanical weathering) The processes of weathering by which physical actions such as frost wedging break down a rock into fragments, involving no chemical change.

dissolution
A chemical reaction in which a solid material is dispersed as ions in a liquid. Example: Halite (NaCl) undergoes dissolution when placed in water.

divergent boundary
Boundary between two crustal plates that are pulling apart.

dolostone
A carbonate rock made up predominately of the mineral dolomite, CaMg(C03)2.

dome
An uplift or anticlinal structure, roughly circular in its outcrop exposure, in which beds dip gently away from the center in all directions.

drag fold
A minor fold produced within a weak bed or adjacent to a fault by the movement of surrounding rocks in opposite directions.

drainage basin
The area from which a stream and its tributaries receives its water.