Chemical Weathering
The process by which the internal structure of a mineral is altered by the removal and/or addition of elements.
Erosion
The incorporation and transportaion of material by a mobile agent, such as water,wind, or ice.
Hydrolysis
A chemical weathering process in which minerals are altered by chemically reacting with water and altered by chemically.
Mechanical Weathering
The physical disintergration of rock, resulting in smaller fragments.
Oxidation
The removal of one or more electrons from an atom or ion. So named because elements commonly combine with oxygen.
Laterite
A red, highly leached soil type found in the tropics that is rich in oxides of iron and aluminum.
Regolith
The layer of rock and mineral fragments that nearly everywhere covers Earth's land surface.
Soil
A combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant growth.
Spheroidal Weathering
Any weathering process that tends to produce a spherical shape from an initially blocky shape.
Talus
An accumulation of rock debris at the base of a cliff.
Anthracite
A hard, metamorphic form of coal that burns cleanly and hot.
Beds
Parallel layers of sedimentary rock.
Bituminous Coal
The most common form of coal, often called soft, black coal.
Breccia
A sedimentary rock composed of angular fragments that were lithified.
Cementation
One way in which sedimetary rocks are lithified. As material precipitates from water that percolates through the sediment, open spaces are filled and particles are joined into solid mass.
Clastic Texture
A sedimentary rock texture consisting of broken fragments of preexisting rock.
Compaction
A type of lithification in which the weight of overlying material compresses more deeply buried sediment. It is most important in the fine-grained sedimentary rocks such as shale.
Conglomerate
A sedimentary rock composed of rounded, gravel-size particles.
Cross-bedding
Structure in which relatively thin layers are inclined at an angle to the main bedding. Formed by currents of wind or water.
Evaporite
A sedimentary rock formed of material deposited from solution by evaporation of the water.
Facies
A portion of a rock unit that possesses a distinctive set of characteristics that distinguishes it from other parts of the same unit.
Fossil
The remains or traces of organisms preserved from the geologic past.
Lithification
The process, generally cementation and/or compaction, of converting sediments to solid rock.
Mud Cracks
A feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks.
Permeability
A measure of a material's ability to transmit water.
Porosity
The volume of open spaces in rock or soil.
Reservoir Rock
The porous, permeable portion of an oil trap that yields oil and gas.
Ripple Marks
Small waves of sand that develop on the surface of a sediment layer by the action of moving water or air.
Sediment
Unconsolidated particles created by the weathering and erosion of rock by chemical precipitation from solution in water or from the secretions of organisms, and transported by water, wind, or glaciers.
Sorting
The degree of similarity in particle size in sediment or sedimentary rock.
Strata
Parallel layers of sedimentary rock.
Geothermal Gradient
The gradual increase in temperature with depth in the crust. The average is 30 degrees C per kilometerin the upper crust.
Contact Metamorphism
Changes in rock caused by the heat from a nearby magma body.
Aureole
A zone or halo of contact metamophism found in the country rock surrounding an igneous intrusion.
Confining Pressure
Stress that is applied uniformly in all directions.
Regional Metamorphism
Metamorphism associated with large-scale mountain building.
Shields
A large, relatively flat expanse of ancient igneous and metamorphic rocks within the craton.
Foliation
A term for a linear arrangement of textural features often exhibited by metamorphic rocks.
Slately Cleavage
The type of foliation characteristic of slates in which there is a parallel arrangement of fine-grained metamophic minerals.
Schistosity
A type of foliation characteristic of coarser-grained metamorphic rocks. Such rocks have a parallel arrangement of platy minerals such as the micas.
Index Minerals
A mineral that is a good indicator of the metamorphic environment in which it formed. Used to distinguish different zones of regional metamorphism.
Stress
The force per unit area acting on any surface within a solid.
Tensional Stress
The type of stress that tends to pull a body apart.
Shear
Stress that causes two adjacent parts of a body to slide past one another.
Strain
An irreversible change in the shape and size of a rock body caused by stress.
Confining Stress
Stress that is applied uniformly in all directions.
Deformation
General term for the precesses of folding, faulting, shearing, compression, or extension of rocks as the result of carious natural forces.
Ductile
A type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confining pressures are high.
Elastic
Rock deformation in which the rock will return to nearly its original size and shape when the stress is removed.
Strike
The compass diecti of the line of intersection created by a dipping bed or fault and a horizontal surface. Strike is always perpendicular to the direction of dip.
Dip
The angle at which a rock layer or fault is inclined from the horizontal. The direction of dip is at a right angle to the strike.
Fold
A bent layer or series of layers that were originally horizontal and subsequently deformed.
Anitcline
A fold in sedimentary strata that resembles an arch.
Syncline
A linear downfold in sedimentary strata; the opposite of anticline.
Monocline
A one-limbed flexure in strata. The strata are usually flat-lying or very gently dipping on both sides of the monocline.
Basin
A circular downfolded structure.
Dome
A roughly circular upfolded structure.
Fault
A break in a rock mass along which movement has occurred.
Footwall
The rock surface below a fault.
Hanging Wall
The rock suface immediately above a fault.
Normal Fault
A fault in which the rock above the fault plane has moved down relative to the rock below.
Reverse Fault
A fault in which the material above the fault plane moves up in relation to the material below.
Graben
A valley formed by the downward displacement of a fault-bounded block.
Horst
An elongate, uplifted block of crust bounded by faults.
Strike-Slip Fault
A fault along which the movement is horizontal.
Crevasse
A deep crack in the brittle surface of a glacier.
Seismograph
An instrument that records earthquake waves.
Magnitude
An estimate of the total amount of energy released during an earth-quake, based on seismic records.
Mercalli Intensity Scale
A 12 point scale developed to evaluate earthquake intensity based on the amount of damage to various structures.
Richter Scale
A scale of earthquake magnitude based on the amplitude of the largest seismic wave.
Seismic Wave
A rapidly moving ocean wave, generated by earthquake activity, which is capable of inflicting heavy damage in coastal regions.
P Waves
The fastest earthquake wave, which travels by compression and expansion of the medium.
S Waves
An earthquake wave, slower than a P wave, that traavels only in solids.
Surface Waves
Seismic waves that travel along the outer layer of Earth.
Body Waves
A seismic wave that travels through Earth's interior.
Focus
The zone within Earth where rock displacement produces an earthquake.
Epicenter
The location on Earth's surface that lies directly above the focus of an earthquake.
Subduction
The process by which oceanic lithosphere plunges into the mantle along a convergent zone.
Benioff Zone
The narrow zone of inclined seismic activity that extends from a trench downward into the asthenosphere.
Tsunami
The Japanese word for a seismic sea wave.
Superposition
In any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below.
Original Horizontality
Layers of sediment that are generally deposited in a horicontal or nearly horizontal position.
Cross Cutting Relationships
A principal of relative dating. A rock or fault is younger than any rock through which it cuts.
Unconformity
A surface that represents a break in the rock record, caused by erosion and nondeposition.
Correlate
Establishing the equivalence of rocks of similar age in different areas.
Index Fossils
A fossil that is associated with a particular span of geologic time.