A Hawaiian term for lava flows typified by a rough, jagged, spinose, clinkery surface.

A wedge-shaped body of faulted and folded material accreted (added) to a continental margin in a subaqueous thrust zone.

A pyroclastic rock that consists of angular volcanic fragments that are larger than 64 mm in diameter and that may or may not have a matrix.

An unconsolidated sedimentary deposit intermediate in texture between sand and clay, consisting of particles having diameters in the range of 0.01 to 0.1 mm.

A consolidated aleurite, intermediate in texture between sandstone and shale; esp. siltstone.

Formed or produced elsewhere than in its present place; of foreign origin, or introduced.

An allogenic mineral or rock constituent; e.g. a xenolith in an igneous rock, a pebble in a conglomerate, or a detrital mineral in a placer deposit.

A general term for clay, silt, sand, gravel, or similar unconsolidated detrital material, deposited during comparatively recent geologic time by a stream or other body of running water.

A dark-colored, fine-grained extrusive rock that, when porphyritic, contains phenocrysts composed primarily of zoned sodic plagioclase (esp. andesine) and one or more of the mafic minerals (e.g. biotite, hornblende, pyroxene), with a groundmass composed generally of the same minerals as the phenocrysts, although the plagioclase may be more sodic and quartz is generally present; the extrusive equivalent of diorite.

The angle at which strata or mineral deposits are inclined to the horizontal plane. In most localities, earth movements subsequent to the deposition of the strata have caused them to be inclined or tilted.

Figure 1.1.  The concept of dip angle on Alpine shales [photo by János Kovács]

An unconformity between two groups of rocks whose bedding planes are not parallel or in which the older, underlying rocks dip at a different angle (usually steeper) than the younger, overlying strata; specif. an unconformity in which younger sediments rest upon the eroded surface of tilted or folded older rocks. It is sometimes regarded as a type of nonconformity.

A mineral consisting of anhydrous calcium sulfate: CaSO₄.

A positive or uplifted structure of the continental platform; it is of broad, regional extent (tens to hundreds of thousands of square kilometers) and is produced by slow crustal upwarp during the course of several geologic periods.

A fold, generally convex upward, whose core contains the stratigraphically older rocks.

The layer or shell of the Earth below the lithosphere, which is weak and in which isostatic adjustments take place, magmas may be generated, and seismic waves are strongly attenuated.

Figure 1.2.  Internal stucture of the Earth

Formed or generated in place; specif. said of rock constituents and minerals that have not been transported or that crystallized locally at the spot where they are now found, and of minerals that came into existence at the same time as, or subsequently to, the formation of the rock of which they constitute a part.

Formed or produced in the place where now found.

A fine-grained, dark, mafic igneous rock composed largely of plagioclase feldspar and pyroxene.

Figure 1.3.  The Giant's Causeway: columnar basalt in Northern Ireland [photo by János Kovács]

A great irregular mass of coarse-grained igneous rock with an exposed surface of more than 100 square kilometers, which has either intruded the country rock or been derived from it through metamorphism.

A general term for the rock, usually solid, that underlies soil or other unconsolidated, superficial material.

A montmorillonite-type clay formed by the alteration of volcanic ash. It varies in composition and is usually highly colloidal and plastic.

The branch of geology concerned with the separation and differentiation of rock units by means of the study of the fossils they contain.

Clastic rock made up of angular fragments of such size that an appreciable percentage of rock volume consists of particles of granule size or larger.

Roughly circular, steep-sided volcanic basin with diameter at least three or four times depth. Commonly at summit of a volcano. Contrast with crater.

A sedimentary body which possesses topographic relief, and is composed of autochthonous calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually microbes) which induce carbonate precipitation through their metabolism.

A rock, such as limestone, dolomite, or carbonatite, that consists chiefly of carbonate minerals; specif. a sedimentary rock composed of more than 50% by weight of carbonate minerals. Syn: calcareous rock.

Process by which a binding agent is precipitated in spaces among individual particles of an unconsolidated deposit. Most common cementing agents are calcite, dolomite, and quartz; others include iron oxide, opal, chalcedony, anhydrite, and pyrite.

Weathering of rock material by chemical processes that transform original material into new chemical combinations.

A schist in which the main constituent, chlorite, imparts a schistosity by parallel arrangement of its flakes. Quartz, epidote, magnetite, and garnet may be accessories, the last two often as conspicuous porphyroblasts.

Stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids.

The term chronostratigraphy refers to that aspect of the field of stratigraphy dealing with temporal (time) relations and ages of rock bodies. Chronostratigraphic classification in the field of stratigraphy organizes rocks on the basis of their age or the time of their genesis.

An individual constituent, grain, or fragment of a sediment or rock, produced by the mechanical weathering (disintegration) of a larger rock mass; e.g. a phenoclast.

Consisting of fragments of minerals, rocks, or organic structures that have been moved individually from their places of origin. Syn: detrital; fragmental.

1. A rock or mineral fragment or a detrital particle of any composition (often a crystalline fragment of a clay mineral), smaller than a very fine silt grain, having a diameter less than 4 microns. 2. A loose, earthy, extremely fine-grained, natural sediment or soft rock composed primarily of clay-size or colloidal particles.

An unconsolidated sediment containing 60-80% clay and 40-20% carbonate.

A type of rock foliation, a fabric element that describes the way planar features develop in a rock.

The name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity.

Structurally conformable; said of strata displaying parallelism of bedding or structure. The term may be used where a hiatus cannot be recognized, but cannot be dismissed.

An accumulation of mineral matter formed around a center, or axis, of deposition after a sedimentary deposit has been laid down. Cementation consolidates the deposit as a whole, but the concretion is a body within host rock that represents local concentration of cementing material: enclosing rock is less firmly cemented than the concretion. Commonly spheroidal or disk-shaped and composed of such cementing agents as calcite, dolomite, iron oxide, or silica.

An accumulation of mineral matter formed around a center, or axis, of deposition after a sedimentary deposit has been laid down. Cementation consolidates the deposit as a whole, but the concretion is a body within host rock that represents local concentration of cementing material: enclosing rock is less firmly cemented than the concretion. Commonly spheroidal or disk-shaped and composed of such cementing agents as calcite, dolomite, iron oxide, or silica.

In any profile of a fold, the shape is that of a partial or semicircular or semielliptical cone. Such folds are noncylindrical since none of the folded surfaces contains a straight line parallel to the fold hinge.

Detrital sedimentary rock made up of more or less rounded fragments of such size that an appreciable percentage of volume of rock consists of particles of granule size or larger. (Fig. 5.)

Figure 1.4.  Conglomerate on Jakab Hill, Mecsek Mountains [photo by János Kovács]

Any process whereby loosely aggregated, soft, or liquid earth materials become firm and coherent rock; specif. the solidification of a magma to form an igneous rock, or the lithification of loose sediments to form a sedimentary rock.

A boundary between two plates that are moving toward each other. It is essentially synonymous with subduction zone, but is used in different contexts.

Metamorphism at or very near contact between magma and rock during intrusion.

The convergence of two continental plates, resulting in the formation of mountain ranges.

An environmental facies that are concerned solely with continental environment or determined by the nature of environment; include alluvial, eolian, lacustrine, fluvial and glacial depositional processes.

Portion of ocean floor extending downward from seaward edge of continental shelves. In some places, such as south of Aleutian Islands, slopes descend directly to ocean deeps. In other places, such as off eastern North America, they grad into somewhat gentler continental rises, which in turn lead to deep ocean floors.

Relatively immobile part of the earth, generally large central portion of a continent.

The arrangement of layers at one or more angles to the dip of the formation. A cross-stratified unit is one with layers deposited at an angle to the original dip of the formation. Many investigators have used crossbedding and cross lamination as synonymous for cross-stratification, but it is proposed to restrict the terms crossbedding and cross lamination to a quantitative meaning depending on the thickness of the individual layers or cross strata.

Figure 1.5.  Cross-bedded sand and sandy gravel glaciofluvial sediment (Alaska). [photo by János Kovács]

A metamorphosed limestone; a marble formed by recrystallization of limestone as a result of metamorphism.

A strongly foliated crystalline rock, formed by dynamic metamorphism, that can be readily split into thin flakes or slabs due to the well developed parallelism of more than 50% of the minerals present, particularly those of lamellar or elongate prismatic habit, e.g. mica and hornblende.

A fold that can be generated by a fold axis is called a cylindrical fold. This term has been broadened to include near-cylindrical folds.

A fine-grained extrusive rock with the same general composition as andesite, but having a less calcic plagioclase and more quartz; according to many, it is the extrusive equivalent of granodiorite. Syn: quartz andesite ancient Roman province of Dacia (now part of Romania).

Any surficial accumulation of loose material detached from rock masses by chemical and mechanical means, as by decay and disintegration. It consists of rock fragments, soil material, and sometimes organic matter.

A deposit formed by a debris flow.

Any change from a glassy state to a crystalline state after solidification.

The set of processes that cause physical and chemical changes in sediment after it has been deposited and buried under another layer of sediment. Diagenesis may culminate in lithification.

A dome or anticlinal fold in which the overlying rocks have been ruptured by the squeezing-out of plastic core material. Diapirs in sedimentary strata usually contain cores of salt or shale; igneous intrusions may also show diapiric structure.

A light-colored soft friable siliceous sedimentary rock, consisting chiefly of opaline frustules of the diatom, a unicellular aquatic plant related to the algae.

A breccia-filled volcanic pipe that was formed by a gaseous explosion.

Coarse-grained igneous rock with composition of andesite (no quartz or orthoclase), composed of 75 percent plagioclase feldspars and balance ferromagnesian silicates.

Acute angle that a rock surface makes with a horizontal plane. Direction of dip is always perpendicular to strike.

A fault that strikes approx. perpendicular to the strike of the bedding or cleavage.

Anticlinal fold without clearly developed linearity of crest so that beds involved dip in all directions from a central area, like an inverted but usually distorted cup. Reverse of basin.

The repeating cycle of sand inching up the windward side to the dune crest, then slipping down the dune's slip face allows the dune to inch forward, migrating in the direction the wind blows. The sloping lines or laminations are the preserved slip faces of a migrating sand dune. This structure is called cross-bedding, and can be the result of either wind or water currents.

Tabular discordant pluton.

The violent oscillatory motion of the ground caused by the passage of seismic waves radiating from a fault along which sudden movement has taken place.

A coarse-grained, deep-seated ultramafic rock, consisting essentially of garnet (almandine-pyrope) and pyroxene (omphacite). Rutile, kyanite, and quartz are typically present.

The emission of relatively fluid lava onto the Earth's surface; also, the rock so formed.

1. An accumulation of rock debris produced in place by the decomposition or disintegration of rock; a weathering product; a residue; 2. Fine soil or sand moved and deposited by the wind, as in a sand dune.

Derived from within; said of a geologic process, or of its resultant feature or rock, that originates within the Earth, e.g., volcanism, volcanoes, extrusive rocks. The term is also applied to chemical precipitates, e.g., evaporites, and to ore deposits that originate within the rocks that contain them.

Pertaining to the wind; esp. said of such deposits as loess and dune sand, of sedimentary structures such as wind-formed ripple marks, or of erosion and deposition accomplished by the wind.

As defined by Gilbert (1890), a form of diastrophism that has produced the larger features of the continents and oceans, for example, plateaus and basins, in contrast to the more localized process of orogeny, which has produced mountain chains. Epeirogenic movements are primarily vertical, either upward or downward, and have affected large parts of the continents, not only in the cratons but also in stabilized former orogenic belts, where they have produced most of the present mountainous topography.

Area on surface directly above focus of earthquake.

Situated upon a continental plateau or platform, as an epicontinental sea. (e.g. Baltic sea).

In ore petrology, applied to mineral deposits of later origin than the enclosing rocks or to the formation of secondary minerals by alteration.

According to Grubenmann's classification of metamorphic rocks (1904), the uppermost depth zone of metamorphism, characterized by low to moderate temperatures (less than 300 degrees C) and hydrostatic pressures with low to high shearing stress. Modern usage stresses pressure-temperature conditions (low metamorphic grade) rather than the likely depth of zone.

A rock fragment carried by glacial ice or by floating ice, deposited at some distance from the outcrop from which it was derived, and generally though not necessarily resting on bedrock of different lithology. Size ranges from a pebble to a house-size block.

Said of a rock formed by the solidification of magma; i.e., either an extrusive or an intrusive rock. Most writers restrict the term to its extrusive or volcanic sense.

The worldwide sea-level regime and its fluctuations, caused by absolute changes in the quantity of seawater, e.g., by continental icecap fluctuations.

Any gas or vapor formed beneath the surface of the Earth and escaping either through a conduit or fissure, or from molten lava or a hot spring; an emanation.

Sediments formed from the weathering of pre-existing rocks outside the basin.

The emission of magmatic material (generally lavas) at the Earth's surface; also, the structure or form produced by the process, such as a lava flow, a volcanic dome, or certain pyroclastic rocks.

Assemblage of mineral, rock, or fossil features reflecting environment in which rock was formed.

A sedimentary rock consisting of slightly waterworn, heterogeneous fragments of all sizes, deposited in an alluvial fan and later cemented into a firm rock; it is characterized by persistence parallel to the depositional strike and by rapid thinning downdip.

Surface of rock rupture along which has been differential movement.

The process of fracturing and displacement that produces a fault.

Produced by the action of a stream or river; e.g., sand and gravel deposits.

A marine sedimentary facies characterized by a thick sequence of poorly fossiliferous, thinly bedded, graded deposits composed chiefly of marls, sandy and calcareous shales, and muds, rhythmically interbedded with conglomerates, coarse sandstones, and graywackes.

Layering in some rocks caused by parallel alignment of minerals; textural feature of some metamorphic rocks. Produces rock cleavage.

An impression, cast, outline, or track of any animal or plant that is preserved in rock after the original organic material is transformed or removed.

An organic reef that is directly attached to or borders the shore of an island or continent, having a rough, tablelike surface that is exposed at low tide; it may be more than 1 km wide, and its seaward edge slopes sharply down to the sea floor. There may be a shallow channel or lagoon between the reef and the adjacent mainland.

A small vent in the ground from which volcanic gases and heated groundwater emerge, but not lava.

Coarse-grained igneous rock with composition of basalt.

Roughly spherical, hollow or partially hollow accumulation of mineral matter from a few centimeters to nearly 0.5 m in diameter. Outer layer of chalcedony lined with crystals that project toward hollow center. Crystals, often perfectly formed, usually quartz although calcite and dolomite also found and - more rarely - other minerals. Geodes most commonly found in limestone and more rarely in shale.

A form of opaline silica that is often found around hot springs and geysers.

A monoclinic mineral, 4[(K,Na)(Fe³⁺, Al, Mg)₂ (Si,Al)₄ O₁₀ (OH)₂ ] ; mica group; basal cleavage; dull, light to dark green; soft; a common authigenic mineral in marine sediments, useful for radiometric ages for host rocks.

Metamorphic rock with gneissic cleavage. Commonly formed by metamorphism of granite.

The proportion of material of each particle size, or the frequency distribution of various sizes, constituting a particulate material such as a soil, sediment, or sedimentary rock. The limits of each size are chosen arbitrarily.

A type of bedding in which each layer displays a gradual and progressive change in particle size, usually from coarse at the base of the bed to fine at the top. It may form under conditions in which the velocity of the prevailing current declined in a gradual manner, as by deposition from a single short-lived turbidity current.

Coarse-grained igneous rock dominated by light-colored minerals, consisting of about 50 percent orthoclase, 25 percent quartz, and balance of plagioclase feldspars and ferromagnesian silicates.

A metamorphic rock consisting of even-sized, interlocking mineral grains less than 10% of which have any obvious preferred orientation.

A variety of sandstone generally characterized by hardness, dark color, and angular grains of quartz, feldspar, and small rock fragments set in matrix of clay-sized particles. Also called lithic sandstone.

Folding in which the strata remain parallel or concentric, without structural discordances between them, and in which there are no sudden changes in the form of the folds at depth.

Said of sedimentary rocks of different facies, or said of facies characterized by different rock types. The rocks may be formed contemporaneously or in juxtaposition in the same sedimentation area or both, but the lithologies are different; e.g., facies that replace one another laterally in deposits of the same age. Also, said of a map depicting heteropic facies or rocks.

A break or interruption in the continuity of the geologic record, such as the absence in a stratigraphic sequence of rocks that would normally be present but either were never deposited or were eroded before deposition of the overlying beds.

Said of the texture of an igneous rock composed entirely of crystals, i.e., having no glassy part. Also, said of a rock with such a texture.

An interface indicative of a particular position in a stratigraphic sequence. In practice it is commonly a distinctive very thin bed.

Localized melting region in mantle near base of lithosphere, a few hundred kilometers in diameter and persistent over tens of millions of years. Existence of heat is assumed from volcanic activity at surface.

Of or pertaining to hot water, to the action of hot water, or to the products of this action, such as a mineral deposit precipitated from a hot aqueous solution, with or without demonstrable association with igneous processes; also, said of the solution itself. Hydrothermal is generally used for any hot water but has been restricted by some to water of magmatic origin.

Pertaining to an igneous intrusion, or to the rock of that intrusion, whose depth is intermediate between that of abyssal or plutonic and the surface.

The rock formed by the widespread deposition and consolidation of ash flows and nuée ardentes.

The rock formed by the widespread deposition and consolidation of ash flows and nuée ardentes.

The existence of one or more layers between other layers; e.g. the presence of sheets of lava between sedimentary strata, the occurrence of a particular fossil horizon between fossil zones of a different character, or the inclusion of lamellar particles of one mineral in another in such a way that the inclusions are oriented in planes related to the crystal structure of the host mineral.

A geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age.

A warm period during a glacial period of an ice age that is of insufficient duration or intensity to be considered an interglacial.

Sediments form inside the basin; includes chemical, biochemical, and organic sedimentary rocks.

In geology, a mass of igneous rock that, while molten, was forced into or between other rocks.

A fold whose limbs are parallel.

Said of sedimentary rocks of the same facies, or said of facies characterized by identical or closely similar rock types. The rocks may be formed in different sedimentation areas or at different times or both, but the lithologies are the same; e.g., a facies repeated in vertical succession.

The condition of equilibrium, comparable to floating, of the units of the lithosphere above the asthenosphere. Crustal loading, as by ice, water, sediments, or volcanic flows, leads to isostatic depression or downwarping; removal of load leads to isostatic uplift or upwarping.

A monoclinic mineral, 2[Al₂ Si₂ O₅ (OH)₄ ]; kaolinite-serpentine group; kaolinite structure consists of a sheet of tetrahedrally bonded silica and a sheet of octahedrally bonded alumina with little tolerance for cation exchange or expansive hydration; polymorphous with dickite, halloysite, and nacrite; soft; white; formed by hydrothermal alteration or weathering of aluminosilicates, esp. feldspars and feldspathoids; formerly called kaolin.

According to Grubenmann's classification of metamorphic rocks (1904), the lowermost depth zone of metamorphism, which is characterized by high temperatures (500 to 700 degrees C), mostly strong hydrostatic pressure, and low or no shearing stress. It produces rocks such as high-grade schists and gneisses, granulites, eclogites, and amphibolites. The concept includes effects of high-temperature contact metamorphism and metasomatism. Modern usage stresses temperature-pressure conditions (highest metamorphic grade) rather than the likely depth of zone. Also spelled catazone.

A highly serpentinized porphyritic peridotite, commonly brecciated, which occurs in vertical pipes, dikes, and sills. It is the principal original environment of diamond, but only a small percentage of the known kimberlite occurrences are diamondiferous.

Magnesium-rich ultramafic volcanic rock of high temperature origin.

A concordant igneous intrusion with a known or assumed flat floor and a postulated, dikelike feeder commonly thought to be beneath its thickest point. It is generally plano-convex in form and roughly circular in plan, less than 5 miles (8 km) in diameter, and from a few feet to several hundred feet in thickness.

A flow of pyroclastic material mixed with water. A lahar is often produced when a snow-capped volcano erupts and hot pyroclastics melt a large amount of snow or ice.

The thinnest recognizable layer in a sedimentary rock. Plural, laminae.

A term used by Lombard (1963) for a finely laminated detrital rock of the flysch lithofacies, frequently occurring in geosynclinal successions in natural sequences complementary to typical turbidites. It is finer-grained and thinner-bedded than a turbidite, ranging in thickness from a few millimeters to 30 cm, and is believed to form seaward from turbidites as a bottomset bed of a large delta.

Pyroclastics that may be either essential, accessory, or accidental in origin, of a size range that has been variously defined within the limits of 2 mm and 64 mm.

A geologic deposit bounded by converging surfaces (at least one of which is curved), thick in the middle and thinning out toward the edges, resembling a convex lens. A lens may be double-convex or plano-convex.

Sedimentary rock composed largely of mineral calcite, CaCO₃, formed by either organic or inorganic processes. Most limestones have clastic texture, but nonclastic, particularly crystalline, textures are common.

Iron oxide with no fixed composition or atomic structure; a mineraloid. Always of secondary origin, not a true mineral. Is encountered as ordinary rust or coloring material of yellow clays and soils.

The direction of the angle of dip, measured in degrees by compass direction. It generally refers to true dip, but can be said of apparent dip as well.

A mechanically formed and deposited fragment of a carbonate rock, normally larger than 2 mm in diameter, derived from an older, lithified limestone or dolomite within, adjacent to, or outside the depositional site.

The rock record of any sedimentary environment, including both physical and organic characters. It is a mappable subdivision of a designated stratigraphic unit, distinguished from adjacent subdivisions on the basis of lithology.

Rigid outer layer of earth; includes crust and upper part of mantle. Relatively strong layer in contrast to underlying asthenosphere.

A sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers.

A shallow, nearshore, terracelike part of a submerged lake bed, produced by the combined effects of wave erosion and current deposition, and often extending a considerable distance lakeward from the beach.

Unconsolidated, unstratified aggregation of small, angular mineral fragments, usually buff in color. Generally believed to be wind-deposited; characteristically able to stand on very steep to vertical slopes.

Any accumulation of shells (esp. oysters) in stratified rocks.

The level or ocean depth at which the rate of solution of calcium carbonate just exceeds its combined rate of deposition and precipitation.

A broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake.

Figure 1.6.  Conceptual model of maar formation

A measure of earthquake size, determined by taking the common logarithm base 10) of the largest ground motion observed during the arrival of a P-wave or seismic surface wave and applying a standard correction for distance to the epicenter.

Intermediate zone of earth. Surrounded by crust, it rests on core at depth of about 2,900 km.

Calcareous clay or intimate mixture of clay and particles of calcite or dolomite, usually shell fragments.

A type of wetland that is subject to frequent or continuous flood.[1] Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss.

Heterogeneous mixture of rock materials. Mappable body of deformed rocks that may be several kilometers in length and consists of highly sheared clayey matrix, thoroughly mixed with angular native and exotic blocks of diverse origin and geologic age.

A collective term, first used by Finnish geologists, for metamorphosed mafic rock that has lost all traces of its original texture and mineralogy owing to complete recrystallization.

According to Grubenmann's classification of metamorphic rocks (1904), the intermediate-depth zone of metamorphism, which is characterized by temperatures of 300 to 500 degrees C and moderate hydrostatic pressure and shearing stress. Modern usage stresses temperature-pressure conditions (medium to high metamorphic grade) rather than the likely depth of zone.

According to Grubenmann's classification of metamorphic rocks (1904), the intermediate-depth zone of metamorphism, which is characterized by temperatures of 300 to 500 degrees C and moderate hydrostatic pressure and shearing stress. Modern usage stresses temperature-pressure conditions (medium to high metamorphic grade) rather than the likely depth of zone.

Name of a basalt rock, indicates that the rock has been metamorphosed.

A collective term, first used by Finnish geologists, for metamorphosed mafic rock that has lost all traces of its original texture and mineralogy owing to complete recrystallization.

A process whereby rocks undergo physical or chemical changes or both to achieve equilibrium with conditions other than those under which they were originally formed (weathering arbitrarily excluded from meaning). Agents of metamorphism are heat, pressure, and chemically active fluids.

A schist whose essential constituents are mica and quartz, and whose schistosity is mainly due to the parallel arrangement of mica flakes.

A compact, chertlike rock without cleavage, but with a streaky or banded structure, produced by the extreme granulation and shearing of rocks that have been pulverized and rolled during overthrusting or intense dynamic metamorphism.

A naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.

A mass of naturally occurring mineral material, e.g. metal ores or nonmetallic minerals, usually of economic value, without regard to mode of origin.

A lamprophyre primarily composed of biotite phenocrysts in a groundmass of alkali feldspar and biotite.

The exhalation of carbon dioxide in an area of late-stage volcanic activity; also, the small opening from which the gas is emitted.

A partly marine, partly continental sedimentary facies consisting of a thick sequence of fossiliferous conglomerates, sandstones, shales, and marls, characterized by primary sedimentary structures and sometimes by coal and carbonate deposits. It is more clastic and less rhythmic than the preceding flysch facies.

A local steepening in an otherwise uniform gentle dip.

A mound, ridge, or other distinct accumulation of unsorted, unstratified glacial drift, predominantly till, deposited chiefly by direct action of glacier ice, in a variety of topographic landforms that are independent of control by the surface on which the drift lies.

A sheetlike, allochthonous rock unit, which has moved on a predominantly horizontal surface. The mechanism may be thrust faulting, recumbent folding, or both. The term was first used for the large allochthonous sheets of the western Alps, and it has been adopted into English.

A lava-filled conduit of an extinct volcano exposed by erosion; also called chimney rock or plug.

"Hot cloud." French term applied to highly heated mass of gas-charged lava ejected from vent or pocket at volcano summit more or less horizontally onto an outer slope, down which it moves swiftly, however slight the incline, because of its extreme mobility.

A kerogen-bearing, finely laminated brown or black sedimentary rock that will yield liquid or gaseous hydrocarbons on distillation.

or subspherical particle, up to 5 cm across, produced by the accretion of sedimentary material on to a mobile grain through the action of algae.

Small (< 2 mm in diameter), spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals.

A fine-grained pelagic deposit that contains more than 30% of material of organic origin.

A natural deposit in which a valuable metallic element occurs in high enough concentration to make mining economically feasible.

The process by which structures within fold-belt mountainous areas were formed, including thrusting, folding, and faulting in the outer and higher layers, and plastic folding, metamorphism, and plutonism in the inner and deeper layers.

In petrology, a prefix that, when used with the name of a metamorphic rock, indicates that it was derived from an igneous rock, e.g., orthogneiss, orthoamphibolite; it may also indicate the primary origin of a crystalline, sedimentary rock, e.g., orthoquartzite as distinguished from metaquartzite.

Said of a stratum situated immediately above a particular stratum or above an unconformity.

Said of a fold, or the limb of a fold, that has tilted beyond the perpendicular. Sequence of strata thus appears reversed. Such a fold may be called an overfold.

Lava whose surface is smooth and billowy, frequently molded into forms resembling huge rope coils. Characteristic of basic lavas.

A science that deals with the life of past geological periods, based on the study of fossil remains of plants and animals, and gives information esp. about the phylogeny and relationships of modern animals and plants and about the chronology of the history of the Earth.

A branch of science concerned with the study of pollen of seed plants and spores of other embryophytic plants, whether living or fossil, including their dispersal and applications in stratigraphy and paleoecology.

a. A prefix applied to the names of metamorpic rocks that have been derived from sediments; e.g., paragneiss. b. Prefix meaning beside or nearby. c. Indicating a polymorph. d. Indicating a schist or gneiss derived from a sedimentary protolith. e. A matrix-rich clastic sedimentary rock.

Said of deposits laid down on the landward side of a coast, in shallow fresh water subject to marine invasions.

Paratethys was a large shallow sea that stretched from the region north of the Alps over Central Europe to the Aral Sea in western Asia. The sea was formed during the Oxfordian epoch as an extension of the rift that formed the Central Atlantic Ocean and was isolated during the Oligocene epoch (after 34 million years ago).

Material formed in deep ocean and deposited there. Example: ooze.

A small rounded aggregate (0.1-0.3 mm in diameter) of clay minerals and fine quartz found in some shales and clays, separated from a matrix of the same materials by a shell of organic material, and ascribed to the action of water currents.

An allochem composed of micrite, irrespective of size or origin. Includes both pellets and intraclasts; useful where exact origin is unknown.

A general term for a coarse-grained plutonic rock composed chiefly of olivine with or without other mafic minerals such as pyroxenes, amphiboles, or micas, and containing little or no feldspar. Accessory minerals of the spinel group are commonly present. Peridotite is commonly altered to serpentinite.

The geochronologic unit lower in rank than era and higher than epoch, during which the rocks of the corresponding system were formed. It is the fundamental unit of the worldwide geologic time scale.

A relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock. Phenocrysts often have euhedral forms either due to early growth within a magma or by post-emplacement recrystallization.

Defined as juvenile forming eruptions as a result of interaction between water and magma. They are different from magmatic and phreatic eruptions.

Metamorphic rock with rock cleavage intermediate between slate and schist. Commonly formed by the regional metamorphism of shale or tuff.

A general term for lava that exhibits pillow structure, mostly basalts and andesites that erupted and flowed under water. The ocean floor sodium-rich basalts known as spilites are commonly pillowed.

A vertical conduit through the Earth's crust; e.g., a kimberlite pipe of South Africa, through which magmatic materials have passed. It is usually filled with volcanic breccia and fragments of older rock. As a zone of high permeability, it is commonly mineralized.

One of the small, round or ellipsoidal accretionary bodies in a sedimentary rock, resembling a pea in size and shape, and constituting one of the grains that make up a pisolite. It is often formed of calcium carbonate, and some are thought to have been produced by a biochemical algal-encrustation process. A pisolith is larger and less regular in form than an oolith, although it has the same concentric and radial internal structure.

A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is that of torsionally rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundaries.

A term applied to those basaltic lavas that occur as vast composite accumulations of horizontal or subhorizontal flows, which, erupted in rapid succession over great areas, have at times flooded sectors of the Earth's surface on a regional scale. They are generally believed to be the product of fissure eruptions.

That part of a continent that is covered by flat-lying or gently tilted strata, mainly sedimentary, which are underlain at varying depths by a basement of rocks that were consolidated during earlier deformations. A platform is a part of the craton.

A body of igneous rock formed beneath earth surface by consolidation from magma. Sometimes extended to include bodies formed beneath surface by metasomatic replacement of older rock.

Accumulations of sand and gravel deposited in slack waters on inside of bends of winding, or meandering, river.

Polyphase or multiple metamorphism whereby two or more successive metamorphic events have left their imprint upon the same rocks.

Applied to a conglomerate which contains clasts of many different rock types.

Said of or pertaining to a blastoporphyritic or sometimes porphyroblastic metamorphic rock of igneous origin, or a feldspathic metasedimentary rock having the appearance of a porphyry. It occurs in the lower grades of regional metamorphism.

The accumulation of sequences by deposition in which beds are deposited successively basinward because sediment supply exceeds accommodation. Thus, the position of the shoreline migrates into the basin during episodes of progradation, a process called regression.

A light-colored, vesicular, glassy rock commonly having the composition of rhyolite. It is often sufficiently buoyant to float on water and is economically useful as a lightweight aggregate and as an abrasive. The adjectival form, pumiceous, is usually applied to pyroclastic ejecta.

An individual particle ejected during a volcanic eruption. It is usually classified according to size.

Pyroxene-andesites are the commonest type of andesite and occur in amounts comparable to basalt.

A spherulite composed of radially arrayed acicular crystals.

A form of carbonate mineral formed through evaporation. The evaporation series goes from anhydrite to gypsum and then to Rauwacke. This rock should not be confused with Greywacke, which is formed from sandstones.

An overturned fold, the axial surface of which is horizontal or nearly so.

A sequence of regional metamorphic mineral reactions recorded by the successive mineral assemblages seen in metapelites (metamorphosed or sandy shales) from the Barrovian terrain around Glen Esk in north-eastern Scotland and characteristic of medium regional metamorphic gradients of temperature and pressure.

A geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land.

The geologic age of a fossil organism, rock, geologic feature, or event, defined relative to other organisms, rocks, features, or events rather than in terms of years.

Sedimentation of material derived from a preexisting sedimentary rock, that is, redeposition of sedimentary material.

The term for the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion.

The mineralogical adjustment of relatively high-grade metamorphic rocks to temperatures lower than those of their initial metamorphism, characteristically inducing hydration and hydrous minerals.

A fault on which the hanging wall appears to have moved upward relative to the footwall. The dip of the fault is usually greater than 45 degrees.

A group of extrusive igneous rocks, typically porphyritic and commonly exhibiting flow texture, with phenocrysts of quartz and alkali feldspar in a glassy to cryptocrystalline groundmass; also, any rock in that group; the extrusive equivalent of granite.

A long, narrow elevation of the Earth's surface, generally sharp crested with steep sides, either independently or as part of a larger mountain or hill.

A regional-scale strike-slip fault, e.g., the San Andreas rift in California, with offset measured in hundreds of kilometers.

Aggregate of minerals of one or more kinds in varying proportions.

A diagenezis során cementálódott homok. A cementáló anyag lehet CaCO₃, SiO₂ vagy limonit.

An aquatic ooze or sludge rich in organic (carbonaceous or bituminous) matter.

A supratidal environment of sedimentation, formed under arid to semiarid conditions on restricted coastal plains just above normal high-tide level. It is gradational between the land surface and the intertidal environment. Sebkhas are characterized by evaporite-salt, tidal-flood, and eolian deposits, and are found on many modern coastlines, e.g., Persian Gulf, Gulf of California.

The act or process of settling particles by mechanical means from a state of suspension in air or water.

A large, roughly spheroidal concretion, 8 to 90 cm in diameter, usually of an impure argillaceous carbonate, such as clay ironstone. It is characterized internally by irregular polyhedral blocks formed by a series of radiating cracks that widen toward the center and that intersect a series of cracks concentric with the margins; these cracks are invariably filled or partly filled by crystalline minerals (most commonly calcite) that cement the blocks together. Its origin involves the formation of an aluminous gel, case hardening of the exterior, shrinkage cracking due to dehydration of the colloidal mass in the interior, and vein filling. The veins sometimes weather in relief, thus producing a septate pattern.

A rock consisting almost wholly of serpentine-group minerals, e.g., antigorite and chrysotile or lizardite, derived from the alteration of ferromagnesian silicate minerals, such as olivine and pyroxene. Accessory chlorite, talc, and magnetite may be present.

The process of hydrothermal alteration by which magnesium-rich silicate minerals (e.g., olivine, pyroxenes, and/or amphiboles in dunites, peridotites, and/or other ultrabasic rocks) are converted into or replaced by serpentine minerals.

A fine-grained detrital sedimentary rock, formed by the consolidation (esp. by compression) of clay, silt, or mud.

A large area of exposed basement rocks in a craton, commonly with a very gently convex surface, surrounded by sediment-covered platforms; e.g., Canadian Shield, Baltic Shield. The rocks of virtually all shield areas are Precambrian.

Figure 1.7.  The Baltic Shield near Turku [photo by Zoltán Karancsi]

The introduction of, or replacement by, silica, generally resulting in the formation of fine-grained quartz, chalcedony, or opal, which may fill pores and replace existing minerals.

A concordant pluton that is substantially wider than it is thick. Sills form within a few kilometers of the Earth's surface.

A type of fumarole, the gases of which are characteristically sulfurous.

Figure 1.8.  Solfatara on Vulcano, Eolian Islands [photo by János Kovács]

A low, steep-sided cone of small pyroclastic fragments built up on a fissure or vent. Also known as agglutinate cone; volcanello.

A rounded or spherical mass of acicular crystals, commonly of feldspar, radiating from a central point. Spherulites may range in size from microscopic to several centimeters in diameter.

A time-stratigraphic unit next in rank below a series and corresponding to an age; it generally consists of several biostratigraphic zones. It is the most important unit for long-range correlation.

The science of rock strata. It is concerned not only with the original succession and age relations of rock strata but also with their form, distribution, lithologic composition, fossil content, geophysical and geochemical properties; indeed, with all characters and attributes of rocks as strata; and their interpretation in terms of environment or mode of origin, and geologic history. All classes of rocks, consolidated or unconsolidated, fall within the general scope of stratigraphy. Some nonstratiform rock bodies are considered because of their association with or close relation to rock strata.

An actual rock succession, chosen at a particular locality (the type locality) to act as the standard comparison for all other chronostratigraphic or lithostratigraphic units of its ilk.

A bed or layer of rock; strata, more than one layer.

One of multiple scratches or minute lines, generally parallel, inscribed on a rock surface by a geologic agent, i.e., glaciers, streams, or faulting.

Direction of line formed by intersection of a rock surface with a horizontal plane. Strike is always perpendicular to direction of dip.

Fault in which movement is almost in direction of fault's strike.

A structure produced by sediment trapping and/or precipitation as a result of the growth of cyanophytes (blue-green algae). It has a variety of gross forms, from nearly horizontal to markedly columnar, domal, or subspherical.

Said of conditions and processes, such as erosion, that exist or operate in the open air on or immediately adjacent to the land surface; or of features and materials, such as eolian deposits, that are formed or situated on the land surface. The term is sometimes considered to include fluvial.

The process of one lithospheric plate descending beneath another.

Said of a stratum situated immediately under a particular higher stratum or below an unconformity; syn: underlying.

Said of conditions and processes, or of features and deposits, that exist or are situated in or under the sea or ocean.

A group of rock units or strata that succeed one another in chronological order.

A major fault zone through an orogen or mountain range. Sutures separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories.

A fold of which the core contains the stratigraphically younger rocks; it is generally concave upward.

A compound syncline; a closely folded belt, the broad general structure of which is synclinal. Also called synclinore.

A large depressed structure of continental platformal crystalline basement. There are usually no topographical depression on the syneclise because it's covered by a thicker sedimentary cover.

A geologic structure formed by erosion or normal faulting on a thrust system. In such a system the rock mass (hanging wall block) that has been transported by movement along the thrust is called a nappe. When erosion or normal faulting produces a hole in the nappe where the underlying autochthonous (i.e. un-transported) rocks crop out this is called a window.

Glass spheroid, often with aerodynamic shape, found in strewn fields and associated with impact craters; each cluster of tektites is named for its locality, such as moldavites and australites. A tektite has been shaped by flight through the atmosphere while chilling and ablating and melted by meteorite impact.

Pyroclastic materials that fly from an erupting volcano through the air before cooling, and range in size from fine dust to massive blocks.

The body of rock above a large-scale thrust fault whose surface is horizontal or very gently dipping.

Rock formed by lithification of till.

An igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less alkali feldspar. Quartz is present as more than 20% of the rock. Amphiboles and pyroxenes are common accessory minerals.

In geochemistry, a trace element is a chemical element whose concentration is less than 1000 ppm or 0.1% of a rock's composition. The term is used mainly in igneous petrology. Trace elements will either prefer liquid or solid phase. If compatible with an mineral, it will prefer a solid phase.

Form of calcium carbonate, CaCO₃, which forms stalactites, stalagmites, and other deposits in limestone caves or incrustations around mouths of hot and cold calcareous springs. Sometimes known as tufa, or dripstone.

Rock consolidated from volcanic ash.

a broad flat crater formed by a phreatomagmatic eruption. Tuff rings have low rims and slopes of 3 to 12 degrees.

A tuff containing both pyroclastic and detrital material, but predominantly pyroclasts.

A sediment or rock deposited from, or inferred to have been deposited from, a turbidity current. It is characterized by graded bedding, moderate sorting, and well-developed primary structures.

Metamorphic processes at the extreme upper range of temperatures and pressures, at which partial to complete fusion of the affected rocks takes place and magma is produced.

The volcanic material has been transported and reworked through mechanical action, such as by wind or water.

A form of interbedded mud and ripple-cross-laminated sand, in which "the mud layers overlie ripple crests and more or less fill the ripple troughs, so that the surface of the mud layer only slightly follows the concave or convex curvature of the underlying ripples".

Rock fragment foreign to igneous rock in which it occurs. Commonly inclusion of country rock intruded by igneous rock.