This glossary of geology is a list of definitions of terms and concepts relevant to geology, its sub-disciplines, and related fields. For other terms related to the Earth sciences, see Glossary of geography terms.
The process of determining a specific date (in years or some other unit of time) for an archaeological, geological or paleontological site or artifact.
accident
A sudden discontinuity of ground, such as a fault of great thickness, bed or lentil of unstable ground.[1]
An indurated rock built of large angular rock fragments embedded in an ashy matrix and resulting from explosive volcanic activity. Occurs typically in volcanic vents.
The end member of the plagioclase group of minerals, ideally consisting of silicates of sodium and aluminium, but commonly containing small quantities of potash and lime in addition. Compare barbierite.
A type of rock characterized by a high content of Na2O and K2O relative to the other oxides. They occur throughout the range from ultrabasic to acid, but have their strongest expression in the acid-intermediate part of the range.
A fossil, sediment, or rock that was formed elsewhere and later transported into the location where it is presently found, usually by low angle thrust faulting. An object of this type is referred to as allochthonous. Contrast autochthon.
A crystalline, coarse-grained rock, containing amphibole as an essential constituent, together with feldspar and frequently garnet. Like hornblende schist, amphibolite is formed by regional metamorphism of basic igneous rocks, but is not foliated.
Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal.
A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments.
Said of the texture of igneous rock in which the crystalline components are not distinguishable by the naked eye. Both microcrystalline and cryptocrystalline textures are included.
aplogranite
A light-coloured rock of granitic texture consisting mainly of alkali feldspar and quartz, with subordinate biotite; muscovite may be present.
Sediments consisting essentially of sand grains; that is, of quartz and rock fragments down to 0.005mm in size. Conglomerates, sandstones, grits and siltstones fall into this category. Particle size 2mm to 1/16mm.
Sedimentary rocks of the clay grade, i.e. composed of minute mineral fragments and crystals less than 0.005 mm in diameter, as well as large amounts of colloidal material. Apart from finely divided detrital matter, they consist of the so-called clay minerals, such as montmorillonite, kaolinite, gibbsite and diaspore. Siltstones, mudstones, shales, clays, etc. may all be referred to as argillaceous.
A complex aluminous silicate of calcium, iron and magnesium, crystallising in the monoclinic system, and occurring in many igneous rocks, particularly those of basic composition. It is an essential component of basalt, dolerite and gabbro.
A fossil, sediment, or rock that was formed or produced in the location where it is now found. The term is widely applied to a coal or peat that originated at the place where the plants comprising it grew and decayed and to rocks that have not been displaced by overthrust faulting. An object of this type is referred to as autochthonous. Contrast allochthon.
Igneous rock with low silica content (<54%). The groups ultrabasic, basic, intermediate, and acid constitute a series with progressively increasing SiO2 content.
A particular topography covering much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys.
A branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.
A form of black mica widely distributed in igneous rocks (particularly in granites) as lustrous black crystals, with a singularly perfect cleavage. In composition it is a complex silicate, chiefly of iron and magnesium, together with potassium and hydroxyl.
A rock that forms by the metamorphism of basalt or rocks of similar composition at high pressures and low temperatures, approximately corresponding to a depth of to and a temperature of to.
A structure formed by extension, in which a rigid tabular body such as a bed of sandstone is stretched and deformed amidst less competent beds. See also boudinage.
A failure mode of a rock subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. Typically, folding is thought to occur by simple buckling of a planar surface and its confining volume. The volume change is accommodated by layer parallel shortening the volume, which grows in thickness.
A mineral that is the crystalline form of calcium carbonate (CaCO3), showing trigonal symmetry and a great variety of mineral habits. It is one of the commonest of minerals in association with both igneous and sedimentary rocks.
The process which occurs when a liquid fills a cavity and then solidifies. If the cavity originated from the decomposition of dead organisms, casting may result in the formation of fossils.
Any of a set of allied minerals which may be regarded as hydrated silicates of aluminium, iron, and magnesium. They crystallise in the monoclinic system and are green in colour. They occur as alteration products of such minerals as biotite and hornblende, and also in schistose rocks.
The process by which a newly deposited sediment progressively loses its original water content due to the effects of loading. This forms part of the process of lithification.
The layer of granitic, sedimentary, and metamorphic rocks which form the parts of the Earth's crust that comprise the continents, and the areas of shallow seabed close to their shores (known as continental shelves).
Extended perimeter of a continent and its associated coastal plain, which is covered, during interglacial periods (such as the current epoch), by gulfs, and relatively shallow seas known as shelf seas.
A type of resin produced by plant or tree secretions, particularly identified with the forms of aromatic tree resins used by the cultures of pre-Columbian Mesoamerica as a ceremonially burned incense, as well as for a number of other purposes.
An ellipsoidal or broadly rectangular joint block of granite formed by subsurface weathering in the same manner as a tor but entirely separated from bedrock.
An old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
An inclined sedimentary structure in a horizontal unit of rock. Such tilted structures indicate the type of depositional environment, not post-depositional deformation.
An igneous, volcanic rock with a high iron content. It is an extrusive rock of the same general composition as andesite, but a less calcic feldspar. Synonymous with quartz andesite.
The process of chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism.
A comprehensive non-generic term for a non-sorted or poorly sorted non-calcareous terrigenous sedimentary rock that contains a wide range of particle sizes such as rock with sand or larger particles in a muddy matrix.
A type of intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks; a dome or anticlinal fold of the overlaying rocks which has been ruptured by the squeezing out of the plastic core material.
A monoclinicpyroxene, ideally consisting of silicate of calcium and magnesium, but commonly containing a variable content of FeSi2O6 in addition, and then strictly known as ferriferous diopside.
A type of sheet intrusion referring to any geologic body that cuts discordantly across. A form of minor intrusion injected into the crust during its subjection to tension, the dyke being thin with parallel sides, and maintaining a constant direction in some cases for long distances. Some are more resistant to weathering than the surrounding rock and stand up like walls, while others weather faster and form long narrow depressions.
1. A basic igneous rock of medium grain size, occurring as minor intrusions or in the central parts of thick lava flows.
2. A dark-coloured, basic, igneous rock, composed essentially of pyroxene and a triclinic feldspar with magnetic iron. Considered by some authors to be equivalent to a coarse-grained basalt.
3. A dark, crystalline, igneous rock, chiefly pyroxene with labradorite.
An ultrabasicplutonic rock in which the mafic material is almost entirely olivine, with accessory chromite almost always present. Feldspar mainly plagioclase. See also peridotite.
A general term for hard crust existing as a layer in or on the surface of the upper horizons of a soil in semi-arid climates. Duricrust is formed by the accumulation of solid minerals deposited by water moving upwards by capillary action and evaporating in the dry season. Compare hardpan.
A generally coarse- to medium-grained pyroxene in which are set red garnets. The colour is pistachio green when fresh, but mottled with red when weathered.
Eemian transgression
The portion of the Late Pleistocene spanning the period between 120 Ka and 8m before present.
Any of a set of altered gabbroic and doleritic rocks in which the original pyroxene has been replaced by fibrous amphibole. The rock may be regarded as a first step in the conversion by dynamothermal metamorphism of a basic igneous rock into a green schist.
The displacement of solids (sediment, soil, rock and other particles) usually by the agents of currents such as wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
A piece of rock that deviates from the size and type of rock native to the area in which it rests. Erratics usually occur as stones ranging in size from pebbles to large boulders which were transported by glacial ice, which upon melting left them stranded far from their original source. The name "erratic" is based on the errant location of these boulders.
A long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles in length and, because of their peculiar uniform shape, somewhat resemble railroad embankments.
A mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.
The sum of the lithological and faunal characters of a sediment is its facies. Lithological facies involves composition, grain size, texture, colour, as well as such mass characteristics as current bedding, nature of stratification, ripple marks, etc. Similarly, metamorphic facies involves the degree of crystallisation and the mineral assemblage in a group of metamorphic rocks.
Silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Light minerals (quartz and feldspar) greater than 60% - acid. [Granite (Rhyolite), Adamellite (Rhyo-dacite), Granodiorite (Dacite)]. The term is a mnemonic adjective for igneous rocks having light-coloured minerals in their mode, from "feldspar" and "silica". Contrast mafic.
A conglomerate consisting of surficial sand and gravel cemented into a hard mass by iron oxide derived from oxidation of percolating solution of iron salts. A ferruginous duricrust.
A stack of originally flat and planar surfaces, such as sedimentary strata, which have become bent or curved as a result of plastic (i.e. permanent) deformation.
A non-standard but widely used abbreviation for one billion (1,000,000,000) years, using the metric prefix G (for "Giga") to indicate a quantity of one billion. When not otherwise qualified, it usually indicates 1,000,000,000 years Before Present (or 1,000,000,000 years ago).
A mobile down-warping of the Earth's crust, either elongate or basin-like, measured in scores of kilometres, which is subsiding as sedimentary and volcanic rocks accumulate to thicknesses of thousands of metres.
A hard, brittle, transparent solid, such as used for windows, many bottles, or eyewear, including soda-lime glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride.
A green-coloured, hydrated silicate mineral of potassium and iron that forms on submerged banks. Its occurrence in sands and sandstones is considered an indication of accumulation under marine conditions.
The southern part of the supercontinent of Pangaea which eventually separated to form present-day South America, Africa, India, Australia and Antarctica.
A coarse-grained, often porphyritic, intrusive, felsic, igneous rock containing megascopic quartz, averaging 25%, much feldspar (orthoclase, microcline, sodic plagioclase) and mica or other coloured minerals. Rhyolite is the volcanic equivalent.
An arrangement of mineral grains in a rock of metamorphic origin similar to that of a normal granite, but produced by recrystallisation in the solid and not by crystallisation from a molten condition.
A variety of sandstone generally characterized by its hardness, dark colour, and poorly sorted, angular grains of quartz, feldspar, and small rock fragments (lithic fragments) set in a compact, clay-fine matrix.
An omnibus term lacking precision and applied indiscriminately to basic and intermediate igneous rocks of Lower Paleozoic age in which much chlorite has been produced at the expense of the original coloured minerals, staining the rocks green.
Having the properties of certain rocks of igneous origin which contain some interstitial glass in addition to crystalline minerals. Contrast holocrystalline.
An important rock-forming mineral of complex composition, essentially a silicate of calcium, magnesium and iron, with smaller amounts of potash, soda and hydroxyl. Hornblende crystallises in the monoclinic system and occurs as black crystals or grains in many different types of igneous and metamorphic rocks, including hornblende-granite, syenite, diorite, andesite, hornblende-schist, and amphibole.
A type of rock formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
Fine-grained to aphanitic, buff to dark brown compact rock with parallel streaks or lenticles of black glass, produced by violently explosive volcanoes.
An oxide of iron and titanium, crystallising in the trigonal system; a widespread accessory mineral in igneous rocks, especially those of basic composition.
A chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.
A major unit of the geologic timescale that extended from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, between the end of the Triassic and the beginning of the Cretaceous.
A non-standard but widely used abbreviation for one thousand (1,000) years, using the metric prefix K (for "Kilo") to indicate a quantity of one thousand. When not otherwise qualified, it usually indicates 1,000 years Before Present (or 1,000 years ago).
An irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier and is then deposited on the land surface with further melting of the glacier.
A finely crystalline form of hydrated aluminium silicate occurring as minute monoclinic flaky crystals with a perfect basal cleavage, resulting mainly from the alteration of feldspars under conditions of hydrothermal or pneumatolytic metamorphism.
A distinct type of landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Karst topography is usually characterised by closed depressions or sinkholes, caves and underground drainage.
A fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash.
A time-stratigraphic unit representing the gap in the stratigraphic record. Specifically the missing interval at an unconformity, representing the interpreted space-time value of both hiatus (period of non-deposition), and degradation vacuity (period of erosion).
Igneous rocks usually occurring as dykes intimately related to larger intrusive bodies; characterised by abnormally high contents of coloured silicates, such as biotite, hornblende and augite, and a correspondingly small amount of feldspar, some being feldspar-free.
A term used to denote a light colour in igneous rocks, due to a high content of felsic minerals and a correspondingly small amount of dark, heavy silicates.
Soil liquefaction describes the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or having the consistency of a heavy liquid.
A description of the physical characteristics of a rock unit visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition.
The rigid, outermost rocky shell of a terrestrial planet or natural satellite. The Earth's lithosphere is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more.
lithotype
Specific types of rock classified according to the standards of lithology.
A non-standard but widely used abbreviation for one million (1,000,000) years, using the metric prefix M (for "Mega") to indicate a quantity of one million. When not otherwise qualified, it usually indicates 1,000,000 years Before Present (or 1,000,000 years ago).
A silicate mineral or rock that is rich in magnesium and iron. A mnemonic term for the ferromagnesian and other non-felsic minerals actually present in an igneous rock rich in dark (ferromagnesian) minerals (greater than 60% by volume). Basic [alkali gabbro (alkali basalt), syeno-gabbro (trachybasalt), gabbro (basalt and dolerite)].
An oxide of iron which crystallises in the cubic system. It is attracted by a magnet but does not attract iron itself.
Malmesbury group
An 830 to 980 million-year-old basal group of the Western Cape comprising at least eight distinct formations, including the Tygerberg, Piketberg, Porterville, Berg river, Klipplaat, Moorreesburg, Franschhoek, and Bridgetown formations.
A fine to coarse-grained granoblastic calcium carbonate that effervesces in dilute hydrochloric acid. Often banded with various colours and sometimes veined.
A term applied to rocks which are abnormally rich in dark and heavy ferro-magnesium minerals.
mesocratic
A term applied to igneous rocks which in respect of their content of dark silicates are intermediate between those of leucocratic and melanocratic type, and contain 30–60% of dark heavy minerals.
The solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or the introduction of fluids, i.e. without melting.
A fold with a single limb which produces a sudden steepening of the dip; the rocks, however, soon approximate to horizontal on either side of this flexure.
A glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age.
A geologic period starting 23 million years ago and, depending on definition, either lasting until today or ending 2.6 million years ago with the beginning of the Quaternary.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A normal fault occurs when the crust is extended such that the hanging wall moves downward relative to the footwall. Contrast reverse fault.
One of the plagioclase feldspars consisting of the albite and anorthite molecules combined in the proportions 9:1 to 7:3. It is found especially in the more acid igneous rocks.
An orthosilicate mineral of iron and magnesium which crystallises in the orthorhombic system and occurs widely in the basic and ultramafic igneous rocks. It includes olivine-gabbro, olivine–dolerite, olivine-basalt, and peridotites, among others.
A geologic period and system, the second of six of the Paleozoic Era, spanning the time between 485.4 ± 1.9 to 443.4 ± 1.5 million years ago. It follows the Cambrian and is followed by the Silurian.
Any set of forces and events leading to a large structural deformation of the Earth's lithosphere due to the engagement of tectonic plates. It is the primary mechanism by which mountains are built on continents.
A silicate of potassium and aluminium which crystallises in the monoclinic system and occurs as an essential constituent in granitic and syenitic rocks and as an accessory in many other rock types.
A crescent-shaped lake found within a floodplain or fluvial terrace created by the cut-off and abandonment of an active meander within a river or stream channel.
An alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt or from the interaction between water and basalt melt.
A rock that macroscopically resembles phyllite but that is formed by mechanical degradation (mylonization) of initially coarser rocks (e.g., graywacke, granite, or gneiss).
The set of natural processes and phenomena which result in large-scale movements of portions of the Earth's lithosphere, which is fragmented into multiple tectonic plates of various sizes.
The geologic epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's recent period of repeated glaciations. The Pleistocene is the first epoch of the Quaternary Period and the sixth epoch of the Cenozoic Era.
The geologic period that extends from 5.332 million to 2.588[2] million years Before Present. It is the second-youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene and is followed by the Pleistocene.
Having crystallised at depth within the Earth's crust, used of a rock. Plutonic rocks are slow-cooling and coarse-grained and have relatively low temperatures of final consolidation.
A ladder or grid pattern that occurs during jointing that resembles plumes, oriented perpendicular to the stress, hence which usually form parallel to the upper and lower surfaces of the constituent rock unit.
A non-standard geologic time period immediately preceding the Phanerozoic Eon, divided into several eons of the geologic time scale. It spans from the formation of Earth about 4540 Ma (million years ago) to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance.
The source rock from which a metamorphic, or in some rare cases a sedimentary, rock was formed. In most cases the appropriate sedimentary term is "provenance" rather than "protolith", since the material has been transported.
A fast-moving current of hot gas and rock (collectively known as tephra), which normally hugs the ground and travels downhill or spreads laterally under gravity.
Any of a set of mineral species which, although falling into different systems (orthorhombic, monoclinic, and triclinic), are closely related in form and structure. They are metasilicates of calcium, magnesium, and iron with manganese, and less often with sodium, potassium, zirconium, and fluorine.
A compact, hard, very fine-grained white to creamy white rock which breaks into sharp angular fragments. Quartzite is always associated with other metamorphic rocks, while cemented sandstone is always associated with other sedimentary rocks.
The most recent of the three periods of the Cenozoic Era in the standard geologic time scale. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present.
Over wide areas resulting from deep burial with consequent rise in temperature and static pressure, usually with the help of folding movements that accompany the formation of mountain ranges.
A basalticpumice in which the walls of the vesicles have collapsed, leaving a network of fine, interconnecting glass threads. It is the lightest rock known.
The reconstitution of a rock via revolatisation under decreasing temperatures (and usually pressures), allowing the mineral assemblages formed in prograde metamorphism to revert to those more stable at less extreme conditions.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A reverse fault occurs when the crust is compressed such that the hanging wall moves upward relative to the footwall. Contrast normal fault.
Having the composition and characteristics of clastic rocks, i.e. coarse-grained sedimentary rocks, conglomerates, and breccias, with a particle size of less than 2 mm.
A generic term for any of a set of sedimentary rocks composed of rounded or angular detrital grains, i.e. granules, pebbles, cobbles, and boulders, which are coarser than sand in size.
Sand (with grains up to 2 mm in diameter) in which the grains are cemented together by secondary silica or calcite. Sandstone may be loosely cemented and soft or well cemented and hard, and is usually buff to brownish in color, sometimes reddish, due to the presence of iron oxides, or greenish, due to the presence of glauconite.
A form of potash feldspar identical in composition with orthoclase but physically different, formed under different conditions and occurring in different rock types. It is the high temperature form of orthoclase, into which it inverts at 900 °C (1,650 °F). Occurs in lavas and dyke rocks.
A group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. In French, schist is understood as shale.
A white potash-mica, similar to muscovite in chemical composition and general character but occurring as a secondary mineral, often as a decomposition product of orthoclase.
A fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.
A beach which is armoured with pebbles or small- to medium-sized cobbles (as opposed to fine sand), typically ranging from 2 to 200 millimetres (0.1 to 7.9 in) diameter.
Granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body.
The property of splitting easily along regular, closely spaced planes of fissility, produced by pressure in fine-grained rocks, with the cleavage planes lying in the directions of maximum elongation of the mass.
A smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. This surface is normally striated in the direction of movement.
The process describing the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or which have the consistency of a heavy liquid.
Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. Very poorly sorted indicates that the sediment sizes are mixed (large variance); whereas well sorted indicates that the sediment sizes are similar (low variance).
A geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment. Their chemical composition, gradual growth, and preservation in caves make them useful paleoclimatic proxies. Includes stalactites and stalagmites.
An irregular discontinuity or non-structural fracture in limestone and other sedimentary rocks. Stylolites result from compaction and pressure solution during diagenesis.
A coarse-grained igneous rock of intermediate composition, composed essentially of alkali-feldspar to the extent of at least two thirds of the total, with a variable content of mafic materials, of which common hornblende is characteristic.
A collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are often called talus deposits.
Fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff.
Unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier.
A large, free-standing residual mass (rock outcrop) that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest.
A fine-grained igneous rock type of intermediate composition, in most cases with little or no quartz, consisting largely of alkali-feldspars (sanidene or oligooclase) together with a small amount of coloured silicates such as diopside, horneblende, or mica.
A terrestrial sedimentary rock formed by the precipitation of carbonate minerals from solution in ground and surface waters and/or geothermally heated hot springs.
A rock formed of compacted volcanic fragments, some of which can be distinguished by the naked eye. If the fragments are larger than the rock grades into an agglomerate.
A current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density than the fluid through which it flows.
Tygerberg formation
A component of the PreCambrian Malmesbury group of South Africa
A bubble inclusion within mineral grains (typically monocrystalline quartz), filled with liquid, gas, or both liquid and gas. Vacuoles are randomly distributed in contrast to the oriented bubble trains of Boehm Lamellae.
A geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.
A hydrous silicate mineral that is classified as a phyllosilicate and that expands greatly when heated. Exfoliation occurs when the mineral is heated sufficiently.
Rocks that have crystallised from magma poured out at the surface or introduced at shallow depth. They have cooled relatively rapidly, the grain size of the crystals is small, some part of the melt may solidify as glass, volatiles are lost and anhydrous minerals with high temperatures of crystallisation are present.
A graph that plots wave amplitudes (recorded by seismic reflection and borehole logging) as a function of time, with the positive peaks shaded in a single dark colour.
A rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption.
A method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions.
The emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis of minerals.
In solid mechanics, a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds.
^Kurtz, Jean-Paul, ed. (2007-05-08) [2004]. "geological accident - accident géologique". Dictionary of Civil Engineering. Dictionary of Civil Engineering: English-French. EngineeringPro. Springer Science & Business Media. p. 573. doi:10.1007/b104633. ISBN978-0-306-48474-2. A sudden discontinuity of ground such as fault of great thickness, bed or lentil of unstable ground, etc.
