This is a list of terms used in Bruce Railsback's GEOL 1122 lectures at the University of Georgia. The sole purpose of this list is to clarify Railsback's GEOL 1122 lectures. This is not necessarily a list of terms that must be known for an exam. The definitions are not necessarily those found in standard references - anyone wanting definitions found in standard references should look in standard references.
This list is in order of appearance in lecture. You can use your browser's "Find" function to locate a particular word.
Mineral - a naturally occurring (inorganic) crystalline solid with set chemical composition and characteristic physical properties.
Polymorphs - two minerals with the same chemical composition but with different crystal structures.
Silicate - containing silicon (Si) and oxygen (O).
Silica tetrahedron - the arrangement of Si and O in minerals whereby every Si ion is surrounded by 4 O ions, so that the O ions sit at the corners of a tetrahedron or of a trigonal pyramid.
Mafic - rich in magnesium and iron.
Sialic - rich in silica and aluminum.
Felsic - rich in silica and aluminum.
Rock- a naturally occurring solid mass consisting of one or more minerals or mineraloids.
Igneous Rocks - rocks generated by cooling of magma.
Magma - molten minerals plus volatiles.
Aphanitic - consisting partly or entirely of crystals so small that they are invisible to the naked eye.
Phaneritic - consisting entirely of crystals large enought that they are visible to the naked eye.
Dike - a body of intrusive igneous rock that cuts across pre-existing rocks.
Sill - a body of intrusive igneus rock that is concordant with layering in surrounding pre-existing rocks.
Pluton - a large body of intrusive igneous rock.
Batholith - a huge (state-sized) body of intrusive igneous rock.
Lava - flowing magma, or the solidified equivalent thereof.
Volcanic Ash - very fine-grained volcanic material erupted explosively from a volcano.
Fissure Eruption - an eruption of basalt flowing away from a crack in the earth.
Flood Basalt - a thin but areally extensive mass of basalt, usually the result of a fissure eruption.
Shield volcano - a volcano, usually of basalt, with sides with low (2° to 10°) slopes.
Composite Volcano - a volcano consisting of both lava and volcanic ash, with sides as steep as 30° near its top.
Stratovolcano - see Composite Volcano.
Weathering - disintegration and decomposition of rocks at earth surface because of their instability at earth surface presure and temperature.
Mechanical Weathering - physical breakdown of rock into small pieces that are mineralogically and chemically unchanged from the original material; usually accomplished by fracturing, freezing and thawing, and root wedging.
Exfoliation -development of fractures parallel to the earth surface as the result of release of pressure due to the erosion of overlying rock.
Chemical Weathering - chemical alteration or breakdown of a rock to produce dissolved ions and/or minerals not present in the original material.
Soil - an untransported (or only slightly transported) residue from weathering of underlying rock, plus organic or mineral material formed in place.
Paleosol - an ancient soil now buried under younger sediments or rocks.
Erosion - physical removal of particles from their original location on the earth surface by flowing water , air, or ice.
Transportation - Carrying of eroded materials by flowing water, air, or ice to a place of deposition.
Deposition of Sediments - Physical settling of mineral and other material from water, air, or ice, or chemical or biological precipitation of minerals from water (usually seawater).
Lithification - process by which loose grains of sediment become a solid rock. Includes cementation and compation.
Cementation - formation of new minerals between grains of a sediment, as the result of chemical precipitation from porewaters flowing through the sediment.
Compaction - squeezing or suturing of grains of a sediment, and resultant loss of porosity of the sediment.
Sedimentary Rock - a rock consisting of lithified sediment.
Siliciclastic - consisting of sedimentary grains (clasts) derived from the weathering of a silicate-bearing rock.
Conglomerate - a rock consisting of rounded clasts more than 2mm in size.
Sandstone - a sedimentary rock consisting of sand-sized (1/16 mm to 2 mm) sedimentary particles.
Shale - a sedimentary rock consisting of mud-sized or clay-sized sedimentary particles.
Redbed - a package of siliciclastic rocks (usually conglomerates, sandstones, or shales) rich in iron oxide and thus red in color.
Limestone - a sedimentary rock consisting of particles of calcite (or aragonite), usually as the result of marine deposition by organisms.
Evaporite - a mineral or rock formed by chemical precipitation from saline water as the result of evaporation of that water.
Coal - a sedimentary rock consisting of carbonized plant matter. "Bituminous coal" is a more accurate term for the sedimentary rock, as opposed to "Anthracite" (below).
Chalk - a sedimentary rock consisting of microfossils of calcite.
Chert - (1) a sedimentary rock consisting of microfossils of silica; (2) a sedimentary rock formed by chemical alteration of limestone to a silica-rich compositon.
Metamorphism - change in the texture and mineralogy of a pre-existing rock as the result of increased temperature and pressure (and perhaps in the presence of new fluids).
Metamorphic rock - a rock formed by metamorphism.
Foliation - the parallel (and therefore non-random) orientation of planar minerals in a rock.
Lineation - the parallel (and therefore non-random) orientation of elongate minerals in a rock.
Slate - a foliated metamorphic rock in which crystals as so small as to be invisible to the naked eye.
Schist - a foliated metamorphic rock in which crystals are large enough to be visible to the naked eye.
Gneiss - a layered and foliated metamorphic rock.
Marble - a metamorphic rock generated by metamorphism of limestone.
Quartzite - a metamorphic rock generated by metamorphism of sandstone.
Anthracite - a metamorphic rock generated by metamorphism of (bituminous) coal.
Strata - layers of sediments or of sedimentary rocks.
Stratigraphy - the study of and intepretation of strata.
Lithostratigraphic units - packages of strata defined by lithologic characteristics (i.e., by rock type).
Formations - regionally recognizable (and mappable) lithostratigraphic units usually tens to hundreds of feet thick.
Members - subdivisions of formations.
Beds - individual layers within members.
Groups - packages of formations.
Steno's Principle of Lateral Continuity - the proposition that layers, when deposited, did not end abruptly.
Steno's Principle of Original Horizontality - the proposition that layers that are presently folded or tilted were originally deposited as horizontal layers.
Steno's Principle of Superposition - the proposition that younger layers lie on top of older ones.
Unconformity - a surface in the stratigraphic record caused by erosion.
Angular Unconformity - an unconformity at which strata below the unconformity are not parallel to those above.
Disconformity - an unconformity at which strata below the unconformity are parallel to those above.
Nonconformity - an unconformity at which the rocks below are igneous or metamorphic, rather than sedimentary.
Hiatus - the amount of time not represented by the rock record at an unconformity.
Sequence - a body of strata bounded above and below by unconformities.
Facies - a body of sediment or rock with distinctive physical, chemical, and biological attributes.
Transgression - the movement of facies landward as the result of a relative rise in sea level.
Regression - the movement of facies seaward as the result of a relative drop in sea level.
Deepening-upwards sequence - a vertical sequence of strata in which the higher strata were deposited in deeper depositional environments. A deepening-upwards sequence results from a relative rise in sea level.
Shallowing-upwards sequence - a vertical sequence of strata in which the higher strata were deposited in shallower depositional environments. A shallowing-upwards sequence results from a relative drop in sea level.
Fossils - the remains or traces of prehistoric organisms.
Body Fossil - a fossil that preserves the shape of the organism. Cf. "Trace fossil".
Microfossils - microscopic fossils, including pollen grains and the remains of microscopic organisms such as bacteria, diatoms, forams, and coccolithphores.
Trace Fossils - fossils generated by the activities of organisms, including tracks, trails, and burrows.
Coprolite - fossil feces.
Species - according to the standard biological definition, a collection of organisms with structural, functional, and developmental similarities that in nature can reproduce and produce fertile offspring.
Structural Geology - the study of how stress deforms rocks and of the structures that result from such deformation.
Compression - pushing together; stress in which parallel but opposite forces are directed toward a plane.
Tension - pulling apart; stress in which parallel but opposite forces are directed away from a plane.
Shear - wrenching; stress in which parallel but opposite forces are on opposite sides of a plane.
Brittle Deformation - deformation in which something (e.g., a rock body) is broken into smaller pieces.
Fault - sheared broken surface between bodies or blocks of rock.
Normal fault - an inclined fault along which relative motion of the two blocks is such that the upper block moves down.
Reverse Fault - an inclined fault along which relative motion of the two blocks is such that the upper block moves up.
Thrust fault - a low-angle reverse fault.
Strike-slip fault - a nearly vertical fault along which two blocks move laterally past each other.
Ductile deformation - deformation in which the deformed object maintains its continuity.
Anticline - a fold in which older strata are in the center of the fold, or (in most cases) where strata dip away from the axial plane of the fold.
Syncline - a fold in which younger strata are in the center of the fold, or (in most cases) where strata dip toward the axial plane of the fold.
Continental drift - a theory of crustal deformation in which continents are thought to move through unmoving oceanic crust.
Plate tectonics - a theory of crustal deformation in which plates of continental and/or oceanic crust move across the earth surface.
Divergent plate boundary - boundary between two plates at which plates move apart and new oceanic crust is generated.
Convergent plate boundary - boundary between two plates at which plates move together and old oceanic crust is destroyed or continents collide.
Transform plate boundaries - boundary between two plates at which plates move past each other, so that crust is neither generated or destroyed.
Continental margin - the continental shelf and continental slope.
Passive margin - a continental margin at which no subduction occurs, and at which continental crust and the adjoining oceanic crust are part of one plate. Synonymous with "trailing continental margin" and "Atlantic-type margin".
Active margin - a continental margin at which subduction or tranverse motion occurs, and at which continental crust and the adjoining oceanic crust are parts of two different plates. Synonymous with "leading continental margin" and "Pacific-type margin".
Wilson Cycle - the opeining and closing of an ocean basin, from rifting of continental crust to sea-floor spreading to subduction of oceanic crust to continental collision. Named after Dr. J. Tuzo Wilson.
Fact - see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Hypothesis - see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Theory - see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Multiple Working Hypotheses - see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Evidence- see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Ockham's Razor - see Scientific Thought: Facts, Hypotheses, Theories, and all that stuff, a GEOL 1122 web page.
Strict Uniformitarianism - the proposition that the processes presently acting on the earth, acting at the rates presently observed on the earth, explain the history of the earth.
Conventional Uniformitarianism - The proposition that the processes acting on the earth now and in the relatively recent past explain the history of the earth.
Actualism - The proposition that the natural or physical laws governing present processes on Earth governed the past.
The Pull of the Recent - the inevitable tendency for historical study to yield more detailed knowledge about the more recent past and a less detailed understanding of the more distant past.
Correlation - the act of establishing that two or more things have something in common. Lithologic correlation, for example, establishes that two layers of rock viewed at two different places are (or were) in fact physically connected and thus are (or were) really part of one stratum.
Temporal Correlation - the act of establishing that two or more things are the same age.
Principle of Inclusions - the argument that chunks of rock included in other rocks must be older than their hosts.
Principle of Cross-cutting Relationships - the argument that features that cross-cut other features are younger than the features they cut.
Element - collection of all atoms with same number of protons.
Isotopes - atoms of one element (and thus with same number of protons) but with different atomic weights because of different numbers of neutrons.
Alpha decay - the emission of an alpha particle (two protons + two neutrons) from the nucleus of an atom.
Beta decay - the emission of an electron from the nucleus of an atom, converting a neutron to a proton.
Electron capture - the entry of an electron in the nucleus of an atom, converting a proton to a neutron.
Half-life - the time in which half of a particular parent isotope of a given element decays to its daughter isotope of another element.
On to the second half of this glossary.
If you're a GEOL 1122 student and think a term should be added to this list, please send an email message to Bruce Railsback at rlsbk@gly.uga.edu.
If you think any of the above definitions should be improved, email a complete definition to Bruce Railsback at rlsbk@gly.uga.edu.
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