USGS Logo Geological Survey Bulletin 587
Geology of the Great Smoky Mountains National Park, Tennessee and North Carolina
GLOSSARY
Amphibolite A metamorphic rock composed largely of amphibole and feldspar.
Anticline A fold or arch of stratified rocks in which the strata dip in opposite directions from a common ridge or axis.
Anticlinorium A large anticline composed of smaller anticlines and synclines.
Argillaceous Clayey containing clay minerals or their metamorphic products.
Argillite Dark fine-grained rock without cleavage or schistosity, resulting from low-grade metamorphism of claystone or mudstone.
Arkose A sandstone containing at least 25 percent feldspar usually derived from erosion of granitic rocks.
Augen structure "Eyes" or knots of mineral or rock fragments around which foliation or flaser structure is strongly bent.
Basement A rock mass, usually igneous or metamorphic on which younger rocks have been deposited.
Bedrock Solid rock underlying weathered or transported material.
Cambrian The first period of the Paleozoic Era, from 500 to 600 million years ago.
Clastic A term applied to rocks composed of fragmental material derived from preexisting rocks.
Cleavage The tendency for rocks to split along definite planes which generally have no relation to bedding.
Competent A term applied to rocks capable of sustaining stress without being greatly deformed.
Conformable Describes strata deposited without significant disturbance or removal of previously deposited strata.
Crystalline A term applied to rocks composed wholly of crystalline mineral grains; that is, igneous and metamorphic rocks as distinct from sedimentary rocks.
Current bedded Shows bedding features (crossbedding or ripple mark) indicating deposition by currents of water.
Debris Rock and mineral fragments produced by weathering of rocks. Synonymous with detritus.
Deformation Change of shape or attitude of a rock body by folding, shearing, fracturing, compression, etc.
Detrital Composed of detritus or debris.
Detritas See Debris.
Devonian The fourth period of the Paleozoic Era, from 350 to 400 million years ago.
Dip angle The angle that a tilted or folded rock layer makes with a horizontal surface.
Dolomite A rock composed essentially of the mineral dolomite or (CaMg) CO3.
Erosion The process of disintegration and removal of the rocks at the earth's surface by weathering and moving water, wind, ice, or landslide.
Fault A fracture in the earth's crust along which rock on one side has been displaced relative to rock on the other.
Fauna The animal life existing at a particular time or locality.
Feldspathic Containing feldspar as a principal ingredient.
Flaser structure Lenses of granular material separated by wavy ribbons and streaks of finely crystalline foliated material.
Flora The plant life existing at a particular time or locality.
Foliation Parallel alinement of platy mineral grains or flattened aggregates in a metamorphosed or sheared rock.
Formation A distinctive bed or group of beds selected from a succession of strata for convenience in mapping, description, and reference.
Geosyncline An elongate depositional basin of continental proportions which is filled by sedimentary rocks over a long period of geologic time.
Gneiss A visibly crystalline metamorphic rock possessing mineral layering or foliation but not easily split along foliation surfaces.
Grade (of metamorphic rocks) Refers to the pressure-temperature conditions (low, medium, or high) at which metamorphism occurred.
Granite In the strict sense, a visibly grained igneous rock composed essentially of alkali feldspars and quartz. Commonly, any rock of this composition and texture, whether igneous or metamorphic in origin.
Granitic Pertaining to granite, or similar to granite in composition or texture.
Granitfration Metamorphic transformation of nongranitic rocks to granitelike rocks.
Granodiorite A granitic rock in which soda-lime feldspar is at least twice as abundant as potassium feldspar.
HomoclineRock strata which are tilted uniformly in the same direction.
IgneousA term applied to rocks formed by crystallization or solidification from natural silicate melts, generally at temperatures between 600°C and 1000°C.
IntercalatedA body of material interbedded or interlaminated with another.
InterglacialThe time between major advances of continental glaciers.
IntrusiveA term for rocks, especially igneous rocks, that have penetrated other rocks.
Klippe Part of a thrust sheet isolated by erosion from the remainder of the sheet.
Laminae Thin rock layers, generally less than 1 cm thick, of sedimentary or other origin.
MagmaA hot mobile silicate mixture of crystals and melt within the earth's crust.
MassiveA term applied to thick bodies of homogenous rock uninterrupted by bedding surfaces, fractures, or other mechanical discontinuities.
Megascopic Visible with the unaided eye or with a hand lens.
MetamorphicPertaining, to or resulting from, metamorphism.
Metamorphism The process whereby sedimentary or igneous rocks have been altered by heat and pressure accompanying deep burial in the earth's crust.
Mississippian The fifth period of the Paleozoic Era, from 310 to 350 million years ago.
Ordovician The second period of the Paleozoic Era, from 430 to 500 million years ago.
Paleozoic The second era of geologic time, from 225 to 600 million years ago.
Pegmatite Igneous rock of unusually coarse or varied texture occurring in intrusive bodies generally a few feet to a few hundred feet long.
Phyllite A metamorphic rock similar to schist but finer grained, so that the constituent grains cannot be seen with the unaided eye.
Plutonic A term applied to rocks and processes occurring deep within the earth's crust.
Precambrian Geologic time before the Paleozoic Era.
Quartz monzonite A granitic rock in which the proportions of potassium feldspar and soda-lime feldspar are more or less equal.
Quartzite A sedimentary or metamorphic rock composed largely of quartz grains cemented by silica.
Radioactive A term applied to minerals or rocks containing atoms whose nuclei radiate atomic particles and energy.
Recrystallization Alteration of rocks whereby preexisting mineral grains are destroyed and new ones formed, generally by increased heat and pressure; one of the metamorphic processes.
Schist A visibly crystalline metamorphic rock containing abundant mica or other cleavable minerals so alined that the rock breaks regularly along the mineral grains.
Sedimentary A term applied mainly to rocks formed of fragments of other rocks transported from their source and deposited in water. Applies also to material transported in solution and deposited by chemical or organic agents.
Sequence A succession of stratified rocks.
Sill A tabular body of igneous rock intruded along the bedding surfaces of stratified rocks.
Slickensides Grooves or scratches in rocks made by movement along a fault surface.
Slip The amount of movement on a fault measured on the fault surface. Strike slip is the component of slip measured along the strike of the fault; dip slip is the component measured in the direction of the dip of the fault.
Stratified A term applied to rocks deposited in nearly horizontal layers or strata on the earth's surface.
Strike The direction or bearing of a horizontal line on a sloping bed, fault, or other rock surface.
Syncline A fold in stratified rocks in which the strata on opposite sides usually dip inward toward each other.
Synclinorium A large syncline composed of smaller synclines and anticlines.
Tectonic Pertaining to the larger structural features of the earth's crust and the forces that have produced them.
Thrust fault A fault, commonly of low dip, on which rocks have slid or have been pushed laterally over other rocks.
Turbidity current A heavy mixture of sediment and water that flows along the sea bottom in response to gravity.
Window A hole produced by erosion through a thrust fault exposing the underlying rocks.

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Last Updated: 20-Nov-2006