Glossary of Geology Terms and Definitions

The study of the Earth and the solid and liquid materials it is made up of as well as the structure of these materials, are all, together termed as Geology. The study also consists of the history of formation of volcanoes, rivers, mountains, rocks, glaciers, etc., and the different processes that take place on the Earth's surface, along with the effect of these processes on human life. So, geology also consists of the study of living things/organisms that have inhabited the Earth. The main aim of geological research is the study of the history of planet Earth, along with the gradual changes in the Earth materials and living organisms, due to various processes that took place over vast time periods. The study of these geological processes help to foresee events that can happen in future due to these processes.

The Earth processes that are studied in geology are: earthquakes, landslides, volcanoes, floods, etc. The study of these processes help in avoiding future casualties due to natural disasters, by taking proper preventive measures. The study of Earth materials, like, oil, minerals and metals help to find out the presence of these materials on Earth. And the study of history of Earth helps to understand the climate change of the Earth and how the present climate will influence the future climate. Geology is more like solving the puzzles of nature, of how and why the processes take place. Geology, if taken up as a career, promises a very bright future. Given below is an alphabetical glossary of all geological terms that are commonly used while studying geology.


Aa: Aa is a geological term that is used to refer a basaltic lava that passes with rough, scraggy surface. It is a clinker, fragmented and sharp type of lava, that becomes very viscous on melting. The lava is named "aa" due to the natural response of sound one makes on touching it. The term "aa" has Hawaiian origin.

A-horizon: A-horizon is the uppermost layer of soil that contains leached and organic minerals. It contains less amount of clay and is a layer where any of the biological processes take place. A-horizon is also called biomantle as it contains many of the soil organisms like earthworms, fungi, etc.

Ablation: Ablation, in general, means removal of the surface material from an object, using various erosive processes. While in geology, it refers to the process by which the snow/ice is lost from geological materials like glaciers, snow cover or floating ice. These processes include evaporation, wind erosion, calving, melting, etc.

Absolute Time: The time period used to define the age of the geological term is known as absolute time. This age can be of any geological term that includes any geological event or material. The age can be in seconds, minutes, years or some other unit of time. Radiometric techniques are used to determine the age of the geological term.

Abrasion: Abrasion is a mechanical weathering process, that takes place when mediums like air or water are carrying loose particles of rocks and these particles collide with each other or scratch the surfaces of non moving rocks. Thus, abrasion is a friction between moving particle and stationary rocks. The factors that govern the severity or intensity of abrasion are, concentration, velocity, mass and hardness of the moving particle.

Abyssal Plain: The deepest region of an ocean that contains large, flat or gentle slope area is called abyssal plain. These areas are very difficult to explore due to their presence in the extreme depth of the ocean floor. These abyssal plains are usually found at a depth of 6,500 ft inside the ocean.

Accretion: The general meaning of accretion is growth of an object due to accumulation and adhesion. In geological terms, accretion is a process where a material is added to a landmass or a tectonic plate. The material added can be in the form of seamounts, volcanic arcs or sediments. It is a process by which planets have grown in sizes; by adding smaller bodies to the larger bodies.

Accretionary Wedge: Accretionary wedge is also called accretionary prism and is formed by the process of accretion. Accretionary wedges are mostly made up of sediments accreted on a subducting tectonic plate, at the boundary of a convergent plate. Accretionary wedge can also be made up of marine sediments and volcanic island arcs.

Acidic Rock: Acidic rock is a term that refers to an igneous rock which is made up of light colored minerals. This rock consists of more than 66% of combined or free silica. Thus, acidic rock can also be defined as igneous rock that has maximum silica content. Some of the examples of acidic rocks are rhyolite and granite.

Acid Rain: Acid rain is nothing but rain, that is produced by a combination of water present in atmosphere and oxides that are released on burning of hydrocarbons. This rain contains acidic compounds like nitric acid and sulfuric acid. The emission of chemical compounds react with atmospheric water to create acid. Acid rain leads to damage to crops, infrastructure and forests.

Active volcano: An active volcano is the one that erupts frequently or that has erupted in the past and is expected to erupt in near future again. Mauna Loa is world's largest active volcano.

Aftershock: Aftershock is nothing but tremor in the ground just after the main earthquake took place. Aftershock may even take place two years after the main earthquake has occurred. The magnitude of aftershock is usually less than the main earthquake and takes place near the epicenter of the main earthquake.

Aggradation: Aggradation is a process of increase in elevation of a land form, due to sediment deposition. Usually, aggradation takes place in areas where the amount of sediment deposited is more than the amount of sediment the area can transport.

Algal Mat: Algal mat is a layer of filamentous algae formed in a sequential manner of wetting, algal formation and drying, at the bottom of freshwater or marine water. It is also a layer formed by group of algae that are found in fossils, that are related to carbonate sedimentation.

Alpine Glacier: Alpine glaciers are those glaciers that are formed on the slopes of a mountain. When the size of the alpine glacier grows and fills a valley, it is called valley glacier.

Alluvial Fan: Alluvial fan, as the name suggests is a fan-shaped wedge that is formed by the accumulation of sediments left by a fast flowing stream ,when it slows down and spreads in a fan shape fashion at the canyon exit.

Alluvium: Alluvium is a deposit of a running water source (like stream) and can be made up of clays, gravels, sands and silts. The sediments deposited are in unconsolidated form.

Amphibolite: Amphibolite is the name of the metamorphic rock that is formed by the process of recrystallization. An amphibolite rock consists maximum percentage of amphibole and some amount of plagioclase feldspar and a little or no amount of quartz.

Amygdaloidal: Amygdaloidal is referred to the texture of the volcanic rocks that contain a large number of amygdules. Amygdaloidal means "almond shaped".

Amygdule: Amygdule is a gas cavity made up in a volcanic rock that is filled with secondary minerals like quartz, chlorite, etc.

Andesite: Andesite is a type of rock that mainly consists of plagioclase along with other minerals like biotite, pyroxene, hornblende, etc. It is the most common type of rock found in the volcanic regions of the Earth.

Angle of Repose: The maximum angle at which a heap of an unconsolidated material like soil, sediment or any loose material can stay stable, is called angle of repose. It can also be defined as maximum angle when such loose material is added to the heap and the material comes to rest.

Angular Unconformity: An unconformity that is formed due to the deposition of horizontally parallel strata of sedimentary rocks on eroded or tilted layers. This deposition leads to a angular discordance with horizontal layers that overlay.

Anthracite: Anthracite is a type of coal which has maximum percentage of carbon (92-98%) in it. It is very hard coal with high luster and burns with blue flames and little smoke. Anthracite is commonly referred to as "hard coal".

Anticline: Anticline is a fold in a rock and is convex shaped. This fold is the oldest section of the rock. The term is confused with the general term "antiform", that is used to describe any convex up fold.

Aphanitic: Aphanitic rocks are those igneous rocks, that are made up of very fine crystals that cannot be seen with unaided eyes. These rocks are extrusive rocks that underwent quick cooling to inhibit the crystal growth.

Aplite: Aplite is an intrusive rock that contains maximum percentage of feldspar and quartz. It is a light colored and fine grained rock.

Aquiclude: Aquiclude is soil, sediment or simply a rock, that absorbs water slowly but does not transmit water with great speed enough to act as a supply for spring or well.

Aquifer: Aquifer is a permeable rock that is porous in nature. It stores and transmits groundwater in adequate quantity for supplying wells.

Aquitard: Aquitard is a kind of aquifer rock that stores water and has low permeability. The movement of water through these rocks is slow due to less permeability.

Archean: It is a geologic eon that represents or describes the time period between 3.9 billion years to 2.5 billion years ago.

Aridity Index: The index that represents the ratio of annual evaporation to the solar radiation, that an area received is called aridity index. It gives the degree of deficiency of water in a specific region.

Arkose: A sedimentary rock that has at least 25% feldspar is called arkose. Arkose can be recognized due to the presence of feldspar grains that are angular in shape and pink in color. It is formed by weathering of rocks that contain feldspar.

Arroyo: Arroyo is a dry bed or gulch that fills with water seasonally, due to heavy rains. An arroyo can be man-made or natural.

Artesian well: A well that allows the water in the rocks like aquiclude and aquifer, to reach the surface is called artesian well. It can also be called a well in which the aquifer stone is under pressure to raise the water level.

Aseismic: An aseismic region is a region where earthquake does not occur.

Ash: Ash is made up of fine particles of volcanic gas and rock that are thrown up in the atmosphere after volcanic eruption. It is also referred to as volcanic ash.

Assemblage: It is a group of minerals that describe the characteristics of a rock/facies.

Asthenosphere: Asthenosphere is the upper mantle of the Earth that is present just below lithosphere. It is located at 100 to 200 km below the Earth's crust and extends approximately up to 400 km. This layer is made up of soft and mobile rocks and is called weak zone.

Astrobleme: An old/ancient scar left on Earth's surface, that is circular in shape and is produced due to an impact of comet or meteorite is called astrobleme.

Atoll: An atoll is a circular ring shaped class of coral islands that encloses a lagoon and is surrounded by ocean water.

Augen: Augen means "eyes" in German. Thus augen are mineral grains that are large eye shaped and are found in metamorphic rocks. Some of the common minerals that form augen are quartz, feldspar and garnet.

Aureole: Aureole is a zone that surrounds igneous intrusion and is a zone where contact metamorphism has occurred.

Authigenesis: Authigenesis is a process by which new minerals are formed due to deposition in sedimentary rocks.

Avalanche: A rapid flow of ice down a slope, taking place naturally or due to human activity is called avalanche.

Back-arc Basin: These are basins of submarine that are present between subduction zones and island arcs. These can be found at the boundaries of a few convergent plates that are currently located in Western Pacific Ocean.

Back-arc Spreading: Back-arc spreading is a process where the speed of the subducting plate is more than the overriding plate. It is a process where the overriding plate of subduction zone is stretched to a point of rifting, to make the magma rise into the gap formed by the rift.

Backswamp: Backswamp is an area of floodplain where fine silt and clay deposition occurs after a flood. These are generally found behind natural levees of a stream.

Banded Iron Formation: Also sometimes referred as banded iron ore, it is a typical type of rock that is made up of repeated thin layers of iron oxides (hematite/magnetite) and chert (silica oxide/dioxide). Most of the BIFs are estimated to be formed 2 billion years ago.

Bankfull Stage: Bankfull stage is the height of the water or the water level at which the natural channel gets filled completely. Rise of the water above this level indicates occurrence of flood.

Bar: Bar is a deposition of sediments that generally consists of sand or gravel and is usually formed in river mouths, river, border of a stream or offshore waters. Bar is also an unit of pressure.

Barchan Dune: Barchan dunes are crescent shape dunes formed due to wind action, that move across the desert. While moving, their convex side faces upwind and the steeply slope that is convex, faces downwind. These are usually formed in desert regions with less sand and stable wind directions.

Barrier Island: A barrier island is narrow and long island, made up of sand due to the action of waves that run parallel to the shore. The height of a barrier island can be 6 meters and its length can be up to 100 km.

Basal Sliding: Basal sliding is a process or movement of glacier, where the glacier undergoes thawing at its base. This process usually takes place in glaciers of warmer or temperate areas. The sliding of the glacier due to melting of the ice at its base can be called basal sliding.

Basalt: Basalt is a dark-colored, abundantly found, extrusive, igneous rock which is also one of the important components of oceanic crust. This fine grained rock formed from mafic magma, consists mainly of pyroxene and plagioclase feldspar.

Base Flow: Base flow is a part of streamflow, that arises from precipitation due to soil infiltration and gradually flows through the stream. It is the flow of water that is contributed by drainage of springs, seepage or large lakes.

Base Level: Base level is the elevation where any flowing water source cannot erode any more. It can be called the lowest level up to which a land area can be reduced or eroded by the action of running water.

Basement: Rocks like igneous and metamorphic rocks, present below sedimentary cover or platform are called are called basement.

Basin: Any large depression filled sediment can be called basin. With reference to tectonics, it can be a depression of layers that are circular and syncline (downward curving fold). While with reference to sedimentology, it is an area with a large thick deposition of sediments.

Batholith: Batholith is a very huge mass of intrusive igneous rock that is exposed due to erosion and the eroded surface is spread over an area of about 100 square km.

Bathymetry: Bathymetry is the study of measuring the depths of ocean floors and preparing topographic maps.

Bauxite: It is an important ore of aluminum. Bauxite is a rock that is made up of hydrous aluminum oxides and is a product of weathering in tropical areas.

Bed: Bed is the smallest part of stratigraphic rock series and is a layer of volcanic material or sediment and can be recognized from other layers.

Bedding: Bedding is a feature of sedimentary rocks where the layers with different compositions, arrangement or grain size are piled one above other in an order, with the youngest layer at the top and the oldest layer at the bottom.

Bedding Plane: Bedding plane is a plane that divides different layers of a sedimentary rock, which is composed of different materials.

Bedrock: Bedrock is a solid consolidated rock that underlies the surface of the Earth. This rock may be exposed at some areas and this exposed surface usually consists of unconsolidated materials.

Beheaded Stream: Beheaded stream is a lower part of a stream, whose upper portion is lost due to stream piracy or diversion.

B-Horizon: B-horizon is also called subsoil and is a soil layer that is composed of minerals or clay. It is composed of minerals like aluminum or iron or any organic material that are deposited by the process of leaching. B-horizon is also referred as zone of accumulation.

Berm: Berm is a layer or a narrow pile, formed due to deposition of sediments on a backshore, by the action of storm waves.

Biogenic Sediment: Biogenic sediment is a skeletal deposition that is resulted due to physiological processes or activities of living organisms.

Bioturbation: The displacement or mixing of sediments by animals and plants is called bioturbation.

Black Smoker: A sea vent formed due to superheated water, that flows from Earth's crust to the ocean floor, is called black smoker. This water is mineral rich and when it comes in contact with cold ocean water the minerals deposit on the vent and form a black chimney like structure.

Blowout: Blowout is a sandy, shallow, circular, depression formed due to the action of wind.

Body Wave: A seismic wave that travels or transmits energy through the body of the Earth and not along the Earth's surface is called body wave. This wave transmits energy in all the directions from the earthquake's focus through the interior of the Earth.

Bottomset Bed: Bottomset bed is a layer that is formed on standing water beyond the edge of a growing delta, due to deposition of fine sediments like silt and clay.

Bowen's Reaction Series: Bowen's reaction series is a research work of a geologist named Norman L. Bowen, that explains how the minerals that are now present on Earth have evolved from the mafic magma. It is a continuous series of rock formation where a new mineral is formed due to a reaction between the previous mineral of the series and the magma.

Braided Stream: Braided stream is a type of stream that is made up of a network of number of water channels, that are separated by narrow band of sand and gravel. These channels divide and combine at various parts of the main stream, forming a braid like pattern.

Branchwork Cave: Branchwork cave is a type of cave that contains passages, that are formed in a pattern like tributaries flow in downward direction or in an areal pattern.

Breakwater: Breakwater is a wall that is built parallel to a coast to cease the incoming waves and protect the shore or harbor.

Breccia: Breccia is a type of clastic rock that is made up of angular fragments of minerals or rocks in a matrix form. There are different types of breccia depending on the type of its parent rock , like tectonic breccia, sedimentary breccia, impact breccia, igneous breccia, etc.

Butte: In French, butte means "small hill". Butte is a hill that has flat top, small vertical steep sides and is located at an isolated place. The hill is formed due to erosive action in an area that contains flat sedimentary rocks.

Calcareous: Calcareous is an adjective that is used to describe any soil, sediment or sedimentary rock that either contains a high percentage of calcium carbonate or is entirely made up of calcium carbonate.

Calcarenite: A rock that is formed by the process of water percolation through a mixture of fragments of calcareous shell and quartz sand. During this process, the lime that dissolves in water acts as a cementing material to bond together the total mass. Calcarenite is also known as dune limestone or dune rock.

Caliche: A sedimentary rock that is formed due to hardening of the calcium carbonate deposition is called caliche. During the hardening process, the calcium carbonate in the rock cements together other sediments, like, clay, silt, sand and gravel.

Calving: Also referred to as ice calving, it is a process wherein a mass of ice breaks away from a glacier / iceberg / ice shelf / crevasse. The broken ice mass ends up falling into a water source and usually this ablation of ice, creates more icebergs.

Caprock: Caprock is a type of rock that is highly resistant and overlies a rock that is comparatively less resistant. Ultramafic rocks and sandstone rocks are some of the common types of caprocks.

Carbonate Conservation Depth: The water level in the ocean below which calcium carbonate does not exist is called carbonate conservation depth. Below this level, the calcium carbonate in the ocean is in completely dissolved form.

Carbonate Rocks: A group of sedimentary rocks that is mainly composed of carbonate minerals is called carbonate rocks. These carbonate minerals are usually dolomite and limestone.

Cataclastic Metamorphism: It is a very uncommon type of metamorphism that takes place due to mechanical deformation. It is also called dynamic metamorphism and is related to chief fault planes. The metamorphism takes place due to heat generated by the friction of fault movements.

Cementation: Cementation is a process by which dissolved minerals get deposited in the openings of sediments. This can be called a cementing process where a new rock is formed. Carbonates, iron oxides, silica and quartz are some of the cementing materials.

Cenozoic: Out of the three eras of human history, Cenozoic era is the latest era or the present geologic era. The Cenozoic era began 65.5 million years ago and continues till date.

Chalcedony: Chalcedony is a type of silica that is cryptocrystalline in nature and is made up of very fine intergrowths of moganite and quartz. Both these minerals have different crystal structures. Chalcedony has a waxy luster and can be translucent or semitransparent.

Chalk: Chalk is a type of limestone that is made up of calcite. It is a sedimentary rock that is white, porous and soft in nature. Magnesium silicate and calcium sulfate can also be referred for chalk.

Chemical Remanent Magnetism: Chemical remanent magnetism, abbreviated as CRM, is magnetization acquired by rocks. This magnetic property was acquired by magnetic minerals during the process of diagenesis of sedimentary deposition, following which they aligned themselves to the global magnetic field.

Chemical Sediment: Chemical sediment is a sediment that is formed due to chemical precipitation of water. This sediment is made up of dissolved minerals. The dissolved mineral can be precipitated due to vaporized water or due to extraction of water by living organisms and deposition of minerals on the death of organism.

Chemical Sedimentary Rock: Chemical sedimentary rock is a rock formed by precipitation of minerals from water or any other solution. It can also be called rock that is composed of chemical sediments.

Chemical Weathering: Chemical weathering is a process or a set of chemical reactions that alters the chemical composition of rocks. Oxidation and hydrolysis are some of the most common chemical alteration processes that take place. Exposure of rocks to water and atmosphere leads to chemical weathering.

Chert: Chert is a sedimentary rock that is cryptocrystalline, microcrystalline or microfibrous and is made up of fine grained silica. Chert is found in a number of different colors that include brown, gray, white, rusty red, etc.

C-Horizon: C-horizon is also called regolith and is the layer that lies below the B-horizon. This layer is less organic in nature and very less weathering takes place here.

Cinder Cone: Cinder cone, also called scoria cone, is formed by lava fragments known as cinders, that are formed from volcanic eruptions. It is a conical shaped steep hill with cinders accumulated around the volcanic vent.

Clastic: Clastic rocks are usually referred to as sedimentary rocks that are made up of particles of pre-existing rocks. These particles are called clasts.

Clay: Clay is made up of fine grained materials that are produced through the weathering process. It shows the characteristic of plasticity, depending on the percentage of water added to it. It is a naturally occurring material that can be hardened when heated or dried.

Claypan: Claypan is a layer that contains higher percentage of clay. This layer is compact, impervious and stiff. The speed of water slows down when passing through a claypan.

Cleavage: Cleavage is the tendency of certain rocks or minerals to break along specific planes where weak bonds are present.

Coal: Coal is a combustible sedimentary rock, black or brown in color. It is formed by the decomposition of dead plants and contains more than 50% of carbon compounds.

Coast: Coast is the dry land that is located at the margin of any water body, like, an ocean.

Compaction: Compaction is the process of reduction in porosity of a sediment due to effect of loading of the deposition above it. This compression process changes the shape and orientation of a sediment due to the weight of deposition that overlies it.

Composite Volcano: Also called stratovolcano, composite volcano is a volcano where cinders, lava and other eruptive material layers are arranged in an alternating pattern. These volcanoes are steep sided and the volcanic eruption in these volcanoes is very explosive.

Comprehensive Soil Classification System (CSCS): CSCS is a classification system that is used by soil scientists. This classification is based on the physical and chemical properties of different types of soil.

Compression: Compression is system of forces that reduces the length or volume of rock. Compressive forces act on tectonic plates to create folded mountains.

Concordant: Rocks that lie parallel to the strata are referred to as concordant.

Cone of Depression: Cone of depression is an area created below a well or underground water source, due to pumping action. This depressive area is formed due to faster speed of pumping as compared to the speed required by water to flow through the aquifer.

Conglomerate: Conglomerate is sedimentary clastic rock that is made up of lithified beds of round gravel. The fragments are cemented together with the help of sand.

Constancy of Interfacial Angles: Also called "first law of crystallography", it is actually a law that states that "the angles between the crystal faces of a given species are constant, whatever the lateral extension of these faces or the origin of the crystal, and are characteristic of that species."

Contact Metamorphism: Contact metamorphism is also known as thermal metamorphism, and is the metamorphism that usually occurs in rocks that are located around igneous rocks. It is a consequence of temperature increase due to encroachment of magma. Rocks formed due to contact metamorphism are called contact metamorphic rocks.

Continental Arc: Continental arc is a strip or belt of volcanic mountains lying above a subduction zone on a continental mainland.

Continental Crust: Continental crust is nothing but a layer or part of the Earth's crust that is made up of metamorphic, sedimentary and igneous rocks that form the continents. This layer is on an average 35 km thick and can be maximum 70 km thick in some large mountain ranges.

Continental Deserts: Continental desert is a desert that is located in the interior part of a continent. These deserts are located at such areas where they are far from winds that carry rain clouds.

Continental Ice Glacier: Glaciers that are formed at high latitudes are called continental ice glaciers. These are located in areas where the temperature is too cold even in summer so that snow that was stored in the previous winter does not melt. Such glaciers are found in Arctic, Antarctic and polar regions.

Continental Rise: Continental rise is nothing but the area that is present between the ocean floor and the continental slope.

Crust: Crust is the outermost or uppermost layer of the Earth. It is a part of lithosphere. There are two types of Earth's crust, - continental crust and oceanic crust. The thickness of Earth's crust lies between 7 to 70 kms. It is made up of rocks formed by igneous processes and these rocks are low density rocks.

Dacite: Dacite is a volcanic rock, that is rich in iron content. It is an extrusive igneous rock that is made up of crystalline minerals and plagioclase. The composition of dacite lies between rhyolite and andesite.

Dendritic Drainage: Dendritic drainage is a type of stream / river drainage pattern that takes the shape of branches of deciduous trees. This type of drainage pattern is usually formed in areas where the surface rocks are resistant to erosion in a uniform pattern. It is the most common drainage system (pattern formed by streams or rivers) observed.

Desertification: Desertification is a process that is basically initiated due to human activities and implies conversion of a non-desert land into desert area. This conversion usually takes place due to loss of or gradual destruction of vegetation, like, overgrazing, increase in the rate of erosion, reduction in water table due to overdrafting, overpopulation, etc.

Detrital Sedimentary Rock: Detrital sedimentary rock, as the name suggests, is a type of sedimentary rock that is made up from particles that are derived due to weathering and are transported by air or water. These rocks are composed of the particles of organic debris or pre existed rocks.

Diagenesis: Diagenesis is a process that consists of chemical, biological or physical changes of sediments right from their deposition to form a rock, up to their conversion into a solid rock and does not include metamorphism. Thus it can be called a set of processes that brings change in sediments once they are deposited.

Devonian: Devonian is nothing but a geologic period of time that existed 416 to 359.2 million years ago. This period is said to have occurred during the Palezoic era.

Differential Weathering: There are a few rocks that weather at a different rate as compared to rocks that exist in their surrounding, in spite of being exposed to the same climate or environment. This type of weathering is called differential weathering. This is due to different compositions and resistances of rocks to weathering.

Dolostone: Dolostone, sometimes also called dolomite, is basically a sedimentary rock that is made up of dolomite. Dolomite is a mineral that mainly consists of calcium, carbon, oxygen and magnesium.
This type of rock is very close to limestone and is considered to be formed by the replacement of calcium ions in limestone by magnesium ions.

Dome: Dome is upheaval of Earth's surface which consists of symmetrical anticlines. These domes consist of oldest part of a rock and they are formed through the process of deformation of rocks

Dust Storm: Dust storm takes place when dust particles are moved in large amounts, high into the air or atmosphere over a very large area of an arid region. This storm causes soil erosion in one area and results in deposition in the other.

Earth System: Earth system is a system that consists of everything that takes place between the Earth, its living things, oceans and the atmosphere. In short, it is the interconnection of biological and physical components of the Earth.

Earthquake: Earthquake is a sudden tremor or movement that takes place in the Earth's crust due to fast or explosive release of energy stored in the rocks of the subsurface.

Eon: A 'period' is the smallest time unit in geology. An 'era' comprises two or more periods while an 'eon' is made up of two or more eras. Thus an eon can be called the major or primary division of geologic time scale. Hadean, Archean, Proterozoic and Phanerozoic eons are names of eons in chronological order, with Hadean being the oldest eon and Phanerozoic being the present eon.

Epicenter: An epicenter is a point located on the Earth's surface that is present exactly above the focus point of an earthquake.

Era: As discussed earlier, an era is a unit or division of geologic time and is made up of two or more periods. Paleozoic, Mesozoic and Cenozoic are names of geological eras in chronological order, with Paleozoic being the oldest era.

Erosion: Erosion is a process wherein the surface particles of a rock get worn off or loosened and are transported to some other place by air (wind), water, gravity or ice.

Eutrophication: A process where water bodies, like, lakes, streams or any slowing moving stream acquires excess nutrients that results into increased plant growth and thereby reduces the amount of oxygen in the water body leading to death of other organisms living in the water.

Exfoliation: Exfoliation is a process where weathering of a large rock mass takes place such that the scales, plates or shells of this rock mass get peeled off.

Exfoliation Dome: Exfoliation dome, as the name suggests, is a dome shape formed on a rock as a result of exfoliation. Such domes are usually formed in rocks that are igneous and grained, like granite.

Extrusive Rock: Extrusive rocks are igneous rocks that are formed by quick solidification of flowing lava from Earth's surface. They can also be defined as igneous rocks with very fine particles / grains, formed due to crystallization of magma on Earth's surface.

Fault: A fault is defined as a crack or fracture that divides a rock into two parts. The movement of the rock takes place along this crack.

Fault Gouge: Fault gouge is a type of tectonic rock that is soft, has very small grain size and is found near the faults.

Ferromagnesian: Minerals that contain magnesium and iron ions are called ferromagnesian minerals. Minerals that come under this category are olivines, pyroxenes, etc.

Flint: Flint, also called flintstone, is a type of chert that is hard in nature. It is cryptocrystalline and sedimentary. It can be found in rocks, like, limestone and chalk in the form of nodules.

Flowstone: Flowstone is a common or general term that is used for all the cave deposits that are made up of carbonate compounds or calcite materials. These rocks are formed along the floor or walls of the caves along which water flows.

Foliation: Foliation can be defined as structure or arrangement of a class of minerals in a parallel manner, such that they form sheet like layers. These structures are usually formed in metamorphic rocks as a result of exposure to direct pressure.

Foreshock: Foreshock is a minor shake felt before a main earthquake. It is very difficult to detect foreshock on seismometer and generally a full-scale earthquake follows a foreshock with the same epicenter or somewhere near the epicenter. An earthquake may take place after occurrence of a number of foreshocks.

Fossil: Fossil is an evidence or trace of a dead animal or plant. Footprints imprinted on rocks, bones of ancient humans and animals, shells, etc. make some examples of fossils.

Fractional Crystallization: Fractional crystallization is a process wherein crystals are produced from magma and these crystals are separated from the previous magma. This separation of crystals from the magma changes the composition of the magma and generates igneous rocks with different properties and composition. Due to removal of crystals, the percentage of silica in the magma increases gradually.

Frost Wedging: Frost wedging is a type of physical or mechanical weathering where rocks that were joined together are separated due to expansion of water. This expansion of water takes place in the fractures as a result of freezing. Formation of ice in the cracks increase the frost wedging effect.

Gabbro: Gabbro is a class of igneous rocks that are coarse-grained, intrusive, dark in color and mafic. This group of rocks is similar to basalt in composition and is made up of plagioclase, pyroxene, amphibole and olivine.

Geode: Geode is a rock formation that is spherical in shape, hollow and contains some amount of minerals in it. These are usually observed in sedimentary and volcanic rocks and are cavities that are lined with crystals from inside.

Geologic Time Scale: Geologic time scale is a chronological order of the events that help to explain the formation of rocks and other organisms on Earth over different units of time. Period, era and eon are three basic units or divisions of geologic time scale.

Geyser: Geyser is a natural hot spring that bursts (use another word) hot water and steam in an intermittent manner.

Glaciation: Glaciation is the process of formation, development and establishment of glaciers on the Earth's surface.

Glacier: Glacier is a moving mass of ice that is formed due to accumulation of snow. It moves as a result of gravity or due to its own weight.

Gneiss: Gneiss is metamorphic rock that is coarse and foliated with alternate bands of granular minerals and flaky or dark minerals. Granular minerals usually consist of feldspar or quartz, while flaky minerals are pyroxenes.

Gneissosity: Gneissosity is the pattern of foliation that takes place in rocks like gneiss.

Greenstone: Greenstone is an igneous mafic metamorphic rock that is made up of green colored minerals, like, epidote, amphiboles or chlorite.

Guyot: A seamount whose top is flat due to weathering is called Guyot.

Hardness: This is a property of minerals which indicates the degree of resistance of that mineral. The strength of holding the bonds of the mineral's atoms is specified by hardness of the mineral. To measure the hardness of a particular mineral, it is rubbed with a mineral / substance of known hardness. The relative scale is known as Mohs Hardness Scale.

Hot spot: Hot spot is an area, ranging from 100 to 200 km in width, in the upper mantle of earth (lithosphere). This hot spot contains magma that rises in a plume to form volcanoes. The hot spot may persist for 10 million years or more.

High Level Nuclear Waste: The primary waste that originates from the manufacturing and development of nuclear weapons is called high level nuclear waste. High level nuclear waste is the by-product left in the nuclear reactor after the nuclear fuel is consumed.

Hinge Fault: Angular or rotational movement of a fault on one side of the hinge is called hinge fault. Hinge fault is always perpendicular to the fault plane. In case of the hinge fault, the displacement increases with distance from the hinge.

Hydrologic Cycle: A model that describes the movement of water in the hydrosphere, lithosphere, atmosphere and biosphere. The various processes that are described by the hydrologic cycle are evaporation, percolation, transpiration, infiltration and run-off.

Hydrothermal Deposits: Hydrothernal deposits are those which are formed by the action of hot water and gases related to magmatic source.

Hypocenter: Hypocenter is a point beneath the surface of the earth which is said to be the origin of vibrations. The term hypocenter is used in terms of origin of vibrations in case of earthquake or nuclear explosion.

Hydraulic Gradient: Hydraulic gradient is the gradient or slope between two or more hydraulic head measurements that is divided by the lateral distance between these hydraulic heads (flow path). The hydraulic gradient is dimensionless. It is also called the Darcy Slope.

Hydrograph: Hydrograph is a plot or graph that shows the variation of discharge of water over time. Discharge is the volume of water flowing at a particular location per unit of time.

Hanging Valley: A water tributary in the U-shaped glacial valley that enters the valley at a higher elevation, instead of entering at the same level as a main stream.

Ice Age: Ice age is the name given to the period when the temperature of the Earth is too low and causes expansion of glaciers and ice sheets present in continents and polar regions. Another name for ice age is Pleistocene epoch that started around 2 million years ago and since the polar regions of Earth are still covered with ice sheets, it is believed that we still live in the ice age.

Ice Cap: Ice cap is a small dome shaped sheet of ice that covers a large area of the peak of a mountain.

Igneous Rock: Igneous rocks are those rocks that are formed from molten magma. They are formed on crystallization of the magma, once it cools down.

Index Fossil: Index fossils, also called guide fossils are fossils of living organisms that were present in a particular geologic period. With the help of these fossils, the age of the rock or rock layer in which they are found, can be identified.

Index Mineral: An index mineral is a rock that helps to find out the degree of metamorphism that the parent rock underwent. The degree of metamorphism is the temperature, pressure and the composition of the parent rock.

Inner Core: Inner core is the hottest and as the name suggests, the innermost portion of the Earth core. This core has a radius of 1220 kms and is made up of alloys of iron and nickel. It is present somewhere around 6370 kms below the Earth's crust.

Intermediate Rock: Intermediate rock is an igneous rock whose chemical composition is between the chemical compositions of acidic and basic rocks. Thus it can be called rock with silica content between 50-60 percent.

Intrusive Rock: An igneous rock that is formed from cooling and solidifying of magma inside the Earth's crust, is called intrusive rock. These rocks are formed by intrusion of magma into rocks that preexist.

Isograd: Isograd is a line on Earth's surface or a geological map that joins the points where the degree of metamorphism is same. Thus it can also be defined as a line that divides two different metamorphic zones.

Isostasy: Isostasy is the state of balance of gravitational forces (floating of tectonic plates ) that depress and elevate the Earth's crust. It can be defined as the equilibrium between the forces that tend to depress and buoyancy that raises the lithosphere segment to float on asthenosphere.

Jade: Jade is a gemstone that can be made up of any one of the two metamorphic rocks jadeitite or nephrite which contain silicate minerals. This stone is used in ornaments and is green in color.

Jasper: Jasper is a red, green, yellow or brown colored type of chert that is opaque and cryptocrystalline in nature.

Jetty: Jetty is a protective structure built perpendicular to the coast line to protect the shore from erosion and deposition of sediments due to action of waves.

Joint: Joint is a crack or fracture on the surface of a rock along which no movement took place. Or it can be called a crack that divides a rock into two planes without any relative displacement.

Juvenile Water: Juvenile water is the water or stream that has originated due to volcanic eruptions. It is also called water that is added to the Earth's surface due to volcanic activities.

Jurassic: Jurassic is the geologic time period that existed between 150 million and 200 million years ago. It is a part of Mesozoic era and is sometimes also referred to as "Age of Reptiles" during which dinosaurs existed.

Kame: Kame is an irregular geological feature, formed by deposition of gravel, sand or till in the sunken part of a melting glacier, which eventually ends up on a land surface, due to melting of ice from glaciers.

Karst: Karst is a landscape, landform or topography that is formed or developed in a region with soluble rocks due to the effect or action of ground water. Sinkholes, caves, underground drainage and disappearing streams are some of the typical characteristics of this landscape. Such topography is usually formed in areas that contain dolomite, limestone and other water soluble rocks.

Kettle: Kettle also called kettle hole is a depression formed on the surface of ground due to the melting of glacier ice that is buried.

Komatiite: Komatiite is an igneous rock that is derived from mantle which contains a high percentage of magnesium oxide.

Laccolith: Laccolith is a forced igneous intrusion forced between two layered rocks. The bottom of the intrusion is flat enough, but the top of the intrusion is curved. The intrusion is dome shaped as the pressure of magma is high enough to make the intrusion dome shaped.

Lateral Moraine: Lateral moraine is usually found along the sides of glaciers that occupy a valley. The lateral moraine is till that is carried by a glacier.

Laterite: Laterite is a hard subsurface formed by the deposits of oxides of aluminum and iron because of the weathering of underlying parent rock, due to the water table. Laterite is found in tropical soils where the water table fluctuates as per seasonal changes.

Lava: Lava is molten magma that is discharged through the fissures or volcanic vents. Lava is the molten rock that flows out after the eruption of a volcano.

Lava Dome: Lava dome is a circular structure that is formed by slow extrusion of lava from the volcanic vent or fissures developed when a volcano erupts.

Lava Lake: Lava lake is the accumulation of molten lava in a crater that is formed due to the volcanic eruption. Both the molten lava lake and solidified lava lake are considered as one and the same thing.

Lignite: Lignite is a soft, brown-colored, low-grade coal. Commonly, lignite is called brown coal.

Limestone: Limestone is a sedimentary rock of calcium carbonate and is basically produced by two processes, viz. clastic and non-clastic. In clastic process, limestones are formed from the breakup of depositions of shells and corals due to the wave action and currents in the ocean. In non-clastic process, the limestone is the outcome of lithification of coral reefs and marine organism skeletons.

Lithification: Lithification is a process of consolidation of sediments into sedimentary rocks.

Lithosphere: Lithosphere is the rigid outer shell of earth that consists of crust and a portion of upper mantle of the earth.

Mafic: Mafic is a term used to define an igneous rock that contains higher percentages of magnesium and iron. Hence the name "mafic" (magnesium + ferric). These rocks contain mafic minerals, like, olivine, pyroxene and are dark in color. Examples of mafic rock include gabbro and basalt.

Magma: Magma is nothing but a rock in its molten form and is present below the Earth's crust. It contains crystals, solid suspended particles and dissolved gases from which igneous rocks are formed.

Mantle: Mantle is that internal portion of the Earth which lies between the core and the crust. It is the middle layer of the Earth that is approximately 2780 kms thick and occupies almost 84% of Earth's volume.

Marble: Marble is a rock formed by metamorphism of limestone that consists of maximum percentage of calcite. It is in non-foliated form and is widely used for construction related uses.

Mesozoic Era: Mesozoic era is a part of Phanerozoic eon that existed for a period of 180 million years. It consists of three periods that include Triassic, Jurassic and Cretaceous. This era lies between the Paleozoic and Cenozoic eras and is the era when major tectonic activities took place and the environment was such that new living organisms evolved during this era.

Metamorphic Rock: Rocks that are formed due to the process of metamorphism are called metamorphic rocks. These are rocks that have undergone structural changes due to pressure exerted, extensive heat or action of any chemical.

Metamorphism: Metamorphism is a process that brings changes or alterations in sedimentary or igneous rocks. This alteration takes place without melting the parent rock. The factors that are altered include chemical composition, structure/texture and mineral content of the original rock.

Meteoric Water: Meteoric water is the water that is a result of precipitation of water particles from atmosphere, like, hail, snow, sleet or rain.

Monocline: Monocline is a fold that is made up of different layers with every layer oriented in the same direction.

Mudstone: Mudstone is also called mudrock and is sedimentary rock that is made up of clay size particles.

Nannofossils: Nannofossils are small fossils with a resolution so small that is limited by a light microscope. These nannofossils are studied under an electron microscope.

Natural Bridge: Natural bridge is a naturally formed arch shaped rock formation that is a result of weathering or erosion.

Nodule: Nodule is a mass of different compositions and is more resistant to weathering as compared to the surrounding rocks. Nodule is usually round in shape.

Nonconformity: Nonconformity occurs between metamorphic or igneous and sedimentary rock. Sedimentary rock is deposited over the metamorphic or igneous rock and this process is called nonconformity.

Normal Fault: Normal fault, also called extensional fault, is a fault that is extended in a vertical direction such that the hanging wall is moved downwards with respect to the footwall. Basically, this fault is a sign of tectonic extension.

Normal Polarity: A rock is said to be of normal polarity, or positive polarity, when the magnetic field of the rock is same as that of the earth's magnetic field.

North Magnetic Pole: North magnetic pole of earth is the point on earth where the magnetic field of earth points vertically downwards.

Nuclear Power: Nuclear power is the power that is generated by fusion or controlled fission reactions. The heat produced by this power is used to produce steam to drive the turbines.

Nuées Ardentes: Nuées Ardentes is a hot dense cloud of volcanic ash and gas generated in a Pelean eruption.

Obsidian: Obsidian is a type of igneous rock formed by the process of sudden or quick cooling of lava. This rock has glass like texture and hence it is also called Volcanic glass.

Oceanic Crust: Oceanic crust is nothing but crust that covers the ocean floor or ocean basins. This crust is thinner as compared to continental crust and has 5 km thickness approximately.

Oolite: Oolite, also referred to as egg stone is small, spherical sand size sedimentary rock that is made up through the process of inorganic precipitation of calcium carbonate. This rock contains concentric circles internally and is formed from ooids.

Ore: An ore is nothing but a material that occurs naturally and can be used to extract minerals and metals with the help of mining.

Ore Deposit: An ore deposit is natural collection or accumulation of ore from which valuable metals and minerals can be mined.

Original Horizontality: Original horizontality is one of the laws or principles of geology that states that sedimentary rocks were deposited in a horizontal layers and if any inclination is observed in these layers, then it is due to gravity or other forces that acted upon these layers after the deposition.

Outer Core: Outer core, as the name suggests, is the outer part of the Earth's core that is in liquid form and has a thickness of about 2260 km. It is made up of iron and nickel and is present below the Earth's mantle and above the Earth's inner core.

Outwash: Outwash is the deposition of sediments, sand and gravels by the streams formed due to melting of a glacier.

Oxbow Lake: Oxbow lake is a crescent shaped or U shaped lake that is formed due to cut off or a meander from the main body of a river. This lake is formed due to erosion and deposition in the river channel. The term "oxbow" is used to refer to a part of the river that is U shaped.

Ozone Hole: Ozone hole is a part of upper atmosphere formed due to depletion of the ozone layer.

P -Wave: P-wave is a primary wave which travels away from a seismic event. This wave travels through a solid rock that has a sequence of dilations and compressions of the material of which the rock is made of.

Pahoehoe: Pahoehoe is a basaltic lava flow with a rolling, glassy and smooth surface formed due to quick cooling and solidification of lava.

Paleomagnetism: Paleomagnetism is an ancient magnetic field. This magnetic field can be detected from the orientation of magnetic crystals, in rocks like basalt.

Paleosol: Paleosol is an ancient soil and the composition of this soil may reflect climatic conditions that are significantly different from the climate of the region in which it is found.

Paleozoic Era: Paleozoic Era is an era marked by the presence of fish, amphibians, insects and marine invertebrates.

Parent material: Parent material is a source from which a soil is derived and generally consists of bedrock and sediment.

Pangaea: Pangaea is an early continent from which the present continents are formed due to breaking and spreading of the sea floor.

Parabolic Dune: Parabolic dune is a dune that has a convex leeward slope and concave windward slope. They are generally formed on lake shores and sandy oceans.

Partial Melting: Partial melting of rock is incomplete melting of a rock that is composed of different minerals which have different melting points. The mineral that has a higher melting point remains solid and the material whose melting point is reached, turns into molten magma.

Peat: Peat is a compressed soft brown mass formed by partial decomposition of vegetation formed by water saturation. When peat is dried, it is used as fuel.

Pebble: A small roundish shaped rock fragment that is larger than a granule, is called pebble.

Pedalfer: Pedalfer is a common type of soil found in humid regions and is characterized by abundance of iron oxides and clay minerals, deposited in the B-horizon by leaching.

Pedocal: Pedocal is a soil type found in arid regions and is characterized by accumulation of calcium carbonate in the A- horizon.

Pegmatite: Pegmatite is an igneous rock and the grains of this type of rock are more than a centimeter in diameter, with a granitic composition.

Peléan eruption: Peléan eruption is a type of volcanic eruption which is specially characterized by nuées ardentes and lava domes.

Perched Water Table: Perched water table is the one in which the water level is higher than the normal level of the main water table.

Period: Period is a time unit used in geology which refers to a time period that is greater than an epoch, but lesser than an era.

Permafrost Table: Permafrost table defines the depth of a region where the maximum temperature attained is 0 degree Celsius.

Petroleum: Petroleum in geology is a general term used to refer to natural gas or oil.

Phanerozoic: Phanerozoic is the current eon (longest division of geological time) that began 570 million years ago and is continuing till date.

Phyllite: Phyllite is a metamorphosed mudstone which has a silky sheen that is a coarser grain than slate but less coarse than schist.

Plate: Plate is a segment of the earth's lithosphere which moves due to seismic activity and may include an ocean basin or a continent.

Pipe: Pipe is a vertical passage in the earth's crust that allows the magma at one of its ends to pass to the other end (usually at the surface of earth).

Pirate Stream: Pirate stream is a stream that seizes the headwater of another stream.

Placer: Placer is a mineral deposit at the surface, generated by the denseness of valuable minerals from weathered debris due to the stream currents or waves.

Plate Boundaries: Plates are zones of the earth's lithosphere and the edges of these plates are called plate boundaries.

Plate Tectonics: Plate tectonics is a theory which states that the lithosphere is divided into mobile plates.

Plate Triple Junction: Plate triple junction is a point at which three rifts are issued forth, approximately at an angle of 120 degrees.

Playa: Playa is a flat and broad desert basin that contains a short-lived playa lake.

Pluvial Lake: Pluvial lake is a lake that is formed in the pluvial period.

Pluvial Period: Pluvial time period is a time period in the past when a currently dry land had some moisture content.

Polar Desert: Polar deserts are those deserts in which water is present in the form of ice only and liquid form of water is not present at all.

Polar Glacier: A polar glacier is a glacier that does not melt and whose temperature is always below the freezing period.

Polymetamorphism: Polymetamorphism is a series of events of metamorphic episodes that have made a distinctive influence on the same rock.

Polymorphism: Polymorphism is a situation in which two different crystalline structures have identical chemical composition.

Potentiometric Surface: Potentiometric surface is that surface to which the level of the water rises in an artesian system when the limiting aquitard is pierced.

Proterozoic: Proterozoic era is a geological eon between the Archean and Phanerozoic eons. The Proterozoic era started 2.5 billion years ago and ended 0.57 billion years ago.

Pyroclastic: Pyroclastic is a term that refers to the clastic material formed due to the volcanic eruption in the air through a volcanic vent.

Quarry: Quarry is a mine surface used to extract stones and rocks. The extract obtained, like, sand, gravel, aggregate and dimension stone serve the purpose of building material.

Quarrying: Quarrying is the process by which building materials are extracted from quarries.

Quartz: Quartz is one of the minerals that is found in abundant quantity on the Earth. This mineral can be found in metamorphic, igneous and sedimentary rocks and its chemical composition is mainly of silicon and oxygen in a tetrahedral pattern.

Quartz Arenite: Quartz arenite, also called quartzarenite is a type of sandstone with maximum percentage of quartz.

Quartzite: Quartzite is a metamorphic rock that is made up of quartz grains. It is derived from pure form of sandstone and is a nonfoliated type of metamorphic rock that is durable in nature.

Quaternary Ice Age: The ice age that started somewhere around 2 million years ago and which still continues is called quaternary ice age.

Quick Clay: Quick clay is a type of clay that changes its physical form from solid to liquid in a very short period of time because of any disturbance, like, earthquake or thunder.

Rain Shadow Effect: Rain shadow is a desert/dry area formed along one side of a mountain. The mountain blocks the rain carrying clouds and this results into condensation and precipitation on one side, while the other side does not receive any rain and hence remains dry. This is called rain shadow effect and the dry area of the mountain is called rain shadow.

Rayleigh Wave: Rayleigh Wave is a type of surface seismic wave that is produced during an earthquake.

Rectangular Drainage: Rectangular drainage, as the name suggests, is a pattern of stream where the bends made by the streamflow and the tributaries are at right angles to each other.

Regional Metamorphism: Regional Metamorphism also called Barrovian metamorphism is a metamorphism that has affected rocks spread over a large area.

Reservoir Rock: Reservoir rock is a permeable and porous rock from which natural gas or oil can be obtained.

Rhyolite: An extrusive igneous rock that is formed due to crystallization of silicate materials is called rhyolite. It is also called igneous rock that comes under the category of felsic rocks.

Richter scale: The logarithmic scale that measures the intensity or strength of an earthquake is called Richter scale. The magnitude of the earthquake is measured by finding the logarithm of the amplitude of waves that are generated by the seismograph. A division on the Richter scale represents a tenfold elevation in the amplitude that is recorded by the seismogram. While a Richter scale does not have an upper limit, 9 is considered as standard limit.

Rock: Rock is a naturally occurring aggregate in solid form of minerals, in different percentages. Metamorphic, sedimentary and igneous are the three basic types of rock.

Rock Avalanche: Rock avalanche also called rockslide, is the sudden fall of large volumes of rocks, usually due to earthquake or temperature changes. During a rockslide, rock fragments roll over a steep slope due to the action of gravity.

Rock Cycle: Rock cycle is a closed continuous chain of all the geologic processes right from the formation of a rock till its destruction. It is the change of a rock into various forms, like, igneous, sedimentary and metamorphic. The processes that are involved in this cycle include metamorphism, alteration, weathering, lithification, crystallization, etc.

Rock Flour: Rock flour, also called glacial flour, contains tiny rock particles left due to the melting or erosion of a glacier. It is also referred to as glacial meal.

Rock System: Rock system is similar to rock cycle but it is not a continuous cycle and is an open system that does not return to the starting point.

Rock Glacier: Rock glacier also called talus glacier , is an ice mass that contains rocks and other material with a layer of ice or ice cementation beneath the surface.

S wave: S wave, also called secondary wave or shear wave is a type of seismic wave. This wave makes the rock move in a perpendicular direction (up and down) of movement.

Sandstone: Sandstone, also called arenite, is a sedimentary rock of clastic nature that is made up of fine sand particles. These sand particles are held together with silicate material that acts as cement.

Schist: Schist is a metamorphic rock formed through the process of regional metamorphism. This rock is coarse and it can be easily split into slabs because of its foliated structure. It contains maximum percentage of mica in it.

Sea-floor Spreading: Sea-floor spreading is a process when two oceanic plates get separated. It forms a new sea floor, as magma that rises through the cracks due to separation, spreads on the ocean floor.

Sedimentary Facies: Facies are depositions that reflect certain typical features. Sedimentary facies are collections or accumulations that exhibit features of sedimentary rocks.

Sedimentary Rock: Rocks that are formed due to deposition of sediments from mineral solutions are called sedimentary rocks. Almost 80 percent of Earth's surface is covered by sedimentary rocks. Chalk, sandstone, limestone and dolostone are some examples of sedimentary rocks.

Seismic Gap: Seismic gap is the area or segment of an earthquake susceptible zone that has not undergone tremors when other zones have. It can also be called the fault segment that did not experience earthquake for a long time.

Seismic Sea Wave: Seismic sea wave is popularly known as Tsunami. These waves are produced due to seismic activities of the ocean floor. These waves can be devastating due to the displacement of large volumes of water at very high speed.

Seismic Tomography: Seismic tomography is a technology that uses computers to prepare a three dimensional image of the interior of the Earth. To construct this image, seismic wave velocities recorded at different stations are used.

Seismic Wave: Seismic waves are waves that are generated due to eruption, explosion or earthquake and that travel through the Earth.

Seismograph: Seismograph is an instrument that helps to detect and record the magnitude of an earthquake. It records the amplitude of the seismic waves generated during an earthquake.

Seismology: Seismology is the study of the earthquakes with the help of seismic waves that are generated artificially or naturally.

Seismoscope: Seismoscope is an instrument that helps us to know the occurrence and time of an earthquake.

Shale: Shale is a type of sedimentary rock of clastic nature that is made up of fine clay-like particles.
These rocks are dark in color, usually brown, black or red,

Shield Volcano: Shield volcano is a large cone shaped volcano that is built completely from lava.

Shock Metamorphism: Shock metamorphism is a type of metamorphism that is also called impact metamorphism. This type of metamorphism takes place when a high pressure acts on a rock for a few minutes or few seconds. It is usually observed when a meteorite strikes on the rocks of the Earth.

Silica: Silica is a compound that is crystalline in nature and is made up of quartz, flint, sand, etc.

Sill: Sill is a flat or horizontal mass of igneous rock between two layers of sedimentary rock.

Sinkhole: Sinkhole is a depression formed on a topography due to dissolution of a soluble rock. This soluble rock can be either limestone, dolostone or gypsum.

Slate: Slate is a metamorphic rock of very low-grade and is made up of very fine particles. It is developed from shale and can break into thin sheets due to its foliated nature.

Soil: Soil is a naturally occurring material on Earth's surface that is loose and stratified and may contain living matter.

Soil Texture: Soil texture can be defined as the physical characteristics of a soil that is related to the grain size and the minerals that the soil contains.

Solifluction: Solifluction, also called soil fluction, is when a mass of water-saturated soil moves down a slope area.

Specific Gravity: Specific gravity can be defined as the ratio of density of a substance to the density of water at specific temperature.

Stalactite: Stalactite is a type of dripstone that falls down or hangs from the roof or wall of a cave. It is formed due to precipitation of travertine due to dripping water from the ceilings or walls of the cave.

Star Dune: Star dune is a type of dune that has more than three sides and forms a star like shape. This type of dune is formed when wind blows in more than three directions or when the direction of wind changes frequently.

Strain Seismograph: Strain seismograph can be defined as a seismograph that helps distortion due to earthquake, by finding out the displacement that took place between two points.

Stratification: Stratification is the deposition of sediments in a layered manner, such that the materials can be easily differentiated.

Stratigraphy: Stratigraphy can be defined as the study of rock layers and their formation. This study includes the method of formation of the layer, the age of the rock and other characteristics.

Striations: Striations are small grooves that are formed on the surface of sediments, rocks, pebbles, etc. These are formed due to glacial action.

Subduction Zone: Subduction zone is a boundary where two tectonic plates collide with each other. Island areas, mountain ranges and ocean trenches are some of the topographies formed through the geologic activities in these areas.

Subtropical Deserts: Subtropical deserts are some of the hottest deserts of the Earth with very less rainfall.

Surging Glacier: A glacier which moves rapidly and stagnates at alternate intervals of time is called a surging glacier.

Suture: Suture or suture zone is the area where two continental or converging plates meet through collision. Usually these zones are very high mountain ranges. Example: Himalayas and Alps.

Syncline: Syncline is a fold that is convex in downward direction and the central part of this fold is considered as the youngest part of the rock.

Taconite: Taconite is a type of chert or flint like rock. Taconite is also mined as iron ore.

Tar Sand: Tar sand is a variety of sand containing tar or asphalt.

Terminal Moraine: Terminal moraine is the end point or the maximum extent of a glacier. Terminal moraine is like a mold of debris at the end of a glacier.

Texture: Texture is defined as the physical appearance or characteristics of rocks, like, shape, size, arrangements of the materials present in it, etc.

Thermoremanent Magnetism: Thermoremanent Magnetism is the magnetism present in rocks that has resulted from the orientation of the Earth's magnetic field during the formation of rocks.

Thrust Sheet: Thrust sheet is the body of rock above the thrust fault. The surface of the thrust sheet is horizontal and sometimes even gently dipping.

Tidal Power: Tidal power is the power generated from the tidal motions in the ocean.

Topography: Topography is the set of physical features, both natural and man-made, present on the surface of the Earth. Mountains, valleys, rivers, etc characterize the topography of a particular area.

Transform Fault: Transform fault is a type of strike-slip fault found in mid-ocean ridges. Transform fault is caused due to movement between crustal plates.

Transverse Dune: Transverse dune is a type of dune that is perpendicular to the direction of the wind. Transverse dune is straight and elongated.

Trench: Trench is defined as a long deep depression in the floor of the ocean formed due to the subduction of oceanic plates.

Tufa: Tufa is a rock consisting of either calcium carbonate deposited from springs or volcanic ash. Tufa is also sometimes known as travertine.

Turbidite: Turbidite is the sedimentary deposition caused due to turbid water carrying particles of varying sizes. The coarsest grains get deposited at the bottom while the finer ones are at the top.

Unconformity: Unconformity is a buried surface of erosion that separates two rock masses.

Uniformitarianism: Uniformitarianism is the principle that encompasses the laws of nature, that are constant.

Unloading: Unloading means releasing the pressure of the overlying material. This may get developed in a rock or a joint or a sheet.

Unstratified Drift: Unstratified Drift is a glacial drift composed of rock fragments ranging from clay to boulders.

Upwarped Mountain: Upwarped Mountain is a mountain comprising a broad area of the earth's crust, which has gently arched itself upwards and this deformation or alteration is made up of igneous, metamorphic and sedimentary rocks.

Uranium-thorium-lead Dating: Uranium-thorium-lead dating is a form of isotope dating which is dependent on the half-life of the radioactive isotopes of uranium. In other words, the radioactive isotopes of uranium that decay into the isotopes of lead.

USDA Soil Classification System: USDA Soil Classification System is based on the processes and conditions that are responsible for the formation of different soils.

Valley Train: A valley train is a narrow mass of outwash limited to a valley.

Velocity Profile: Velocity profile is a plot of seismic velocity versus the depth of earth.

Ventifact: Ventifact is a cobble, pebble or boulder that is faceted by wind driven sand.

Vesicle: Vesicle is a cavity in lava that has a gas bubble entrapped in lava during solidification.

Vesicular: Vesicular is a term which refers to an igneous rock containing many vesicles that were formed due to expansion of gases (which were earlier dissolved in lava).

Volcanic Arc: A volcanic arc is an arc shaped chain of islands or mountains formed by plate tectonics. There are two types of volcanic arcs, viz., oceanic volcanic arc and continental volcanic arc.

Volcanic Ash: Volcanic ash comprises sand, rock granules and powder that are thrown up in the air after a volcanic eruption.

Volcanic Cinder: Volcanic cinders are cone shaped and are made from particles and blobs of lava blown from the volcanic vent.

Volcanic Cone: The volcanic cone is formed due to the piling up of ballistically blown loose material.

Volcanic Dome: A volcanic dome is a dome formed over the vent from which the volcano erupts. In case the lava is very viscous, it cannot flow out of the vent, thus forming a dome over the vent.

Volcanic Rock: Volcanic rock is the igneous rock that is formed due to the lava flowing out from the earth's surface.

Volcanism: Volcanism is the process in which the molten lava escapes through the earth's core and becomes cool, to form hard rocks.

Volcanogenic Massive Sulfide Deposit: Volcanogenic Massive Sulfide Deposit is a type of metal sulfide deposit associated with the eruption of a volcano.

Wadati-Benioff zone: Wadati-Benioff zone is a deep and active seismic area on the line of subduction. Wadati-Benioff, also known as Benioff zone, can be up to 700 km deep. The foci of earthquakes cluster along the Wadati-Benioff zone.

Water Table: Water table is defined as the area or surface between the zone of aeration and the zone of saturation. The ground is saturated with water below the surface of water table.

Watershed: A watershed can be defined as the area through which water flows to join a stream or a river. Watershed, also known as drainage basin, separates two adjacent water systems.

Wave Crest: The highest part of a wave is known as the wave crest. A wave crest is opposite to the wave trough, which is the lowest part of a wave.

Weathering: Weathering is defined as the process of breaking down or erosion of rocks caused by exposure to atmospheric agents or weather. Weathering takes place on the surface of the earth.

Well: A well is a deep vertical hole or a shaft, dug to obtain water or oil.

Wilson Cycle: Wilson cycle is defined as the opening and closure of the ocean basin through plate tectonics.

Wind Abrasion: Wind abrasion is the weathering or erosion of rocks caused by the sand particles present in the wind.

Wind Farm: Wind farm is a group or cluster of wind turbines that are located in the same place for generation of electricity. The power plant that makes use of wind turbines for the production of electricity is also known as wind farm.

Wind Power: Wind power is a renewable source of energy derived from the wind with the help of windmills.

Xenolith: Xenolith is a small fragment of older rock with an igneous rock in it.

X-ray diffraction: X-ray diffraction is the diffraction produced in a crystal that helps to know the internal structure of a crystal. X-ray crystallography, usually uses this method.

Yardang: Yardang is a sharp and irregular ridge that is carved by wind and oriented parallel to the direction of wind.

Yazoo-type River: Yazoo-type river is a tributary stream unable to enter the main stream due to natural levees along the main stream. Yazoo-type of river flows in the backswamp area, parallel to the main stream.

Yield Point: Yield pint is the stress limit which produces a deformation in a non-brittle material.

Yucca Mountain: Yucca Mountain is situated in Nevada for storing high level nuclear waste.

Zone of Ablation: Zone of ablation is that zone in glaciers where there is loss of ice due to melting, calving or sublimation into water.

Zone of Accumulation: Zone of accumulation is the area in which the ice accumulates in a glacier.

Zone of Aeration: Zone of aeration is the area or zone below the Earth's surface where air and water are both present in the rock pores and soil.

Zone of Flow: The zone of flow is the zone in a glacier at which the weakened ice crystals flow along the deforming planes.

Zone of Fracture: The zone of fracture is area near the surface of glacier that is somewhat brittle in nature.

Zone of Leaching: Zone of leaching is the upper horizon of soil where the soluble decomposition products are removed due to the movement of gravitational moisture.

Zone of Saturation: The zone of saturation lies just below the zone of aeration that has all pore spaces filled with water.I hope this glossary will help you understand different geologic terms and definitions. I would like to thank my friends Aarti Ramdasi and Madhura P, without whom the glossary could not have been completed.