absolute dating

Quantitate method of dating a geologic substance or event to a specific amount of time in the past.


The deep, flat part of the ocean. Also known as the ocean floor.

abyssal plain

Relatively flat ocean floor, which accumulates very fine grained detrital and chemical sediments.

accretionary wedge

Mix of sediments that form as a subducting plate descends and the overriding plate scrapes material and material is added.

acid rock drainage

Toxic waters rich in heavy metals and often of low pH that come from unregulated mining districts.

active margin

A boundary between continental and oceanic plates that has relative movement, making it a plate boundary.


Forces that cause one substance to stick to another.


Deposition with wind-blown sediment


Earthquake(s) that occur after the mainshock, usually decreasing in amount and magnitude over time.


A sandstone rich in feldspar.


Depositional environments that are involved with rarely-flowing water.


Loose sediment formed by water. This term is typically used by geologists for sediments formed via intermittent water, not rivers.

alpha decay

Radioactive decay where two protons and two neutrons leave the isotope.


(RSi4O11)2, where R is a large number of different cations that can sub in. Can be many colors, but the common form, hornblende, is dark brown to black. Has two cleavages at 54° and 126°. Crystals are typically elongated needles or diamond shapes. Common in many igneous rocks and some metamorphic rocks. Structure is a double chain of silica tetrahedra.


Possesses properties of both acid and base


Height or depth of a wave from the middle point.

angle of incidence

Angle from perpendicular to the ground surface at which light rays hit the ground.  If sun is directly above a point and are hitting the ground directly, then the angle of incidence is 0.

angle of repose

Slope angle where shear forces and normal forces are equal.

angular unconformity

Two rock layers that have different angles of deposition relative to horizontal.


A negatively-charged ion. In geology, this commonly includes elements and molecules like SiO4-4, S-2, SO4-4, and O-2.


Similar to dunes, in that they are ridges of sand that form perpendicular to flow, but internally, the sediments dip up stream. Forms in the upper part of the upper flow regime.


A layer with so little porosity and/or permeability that fluids essentially cannot flow through them and only flow around them.


A rock or sediment that has good permeability and porosity, and allows water to move easily, making it possible to get water for human use.


A layer with lower porosity and/or permeability which allows only minimal and/or slow fluid flow.


A chain of volcanic activity, typically in a curved pattern, rising from a subduction zone. The arc is on the overriding plate, typically a few hundred kilometers from the trench, but parallel to the trench.


Dry riverbed in an arid region.

artesian well

A well which allows pressurized water to reach the surface.


Fault, or movement along a fault, that does not have earthquake activity.


A ductile physical layer of the Earth, below the lithosphere. Movement within the asthenosphere is the main driver of plate motion, as the overriding lithosphere is pushed by this.


The gases that are part of the Earth, which are mainly nitrogen and oxygen.


Strong crystals that do not deform as easily under ductile deformation, and form lens-shaped porphyroblasts.


A depression that occurs in an area that was subject to earlier rifting.


A zone of contact metamorphism that surrounds an intrusion. Since intrusions are typically somewhat round in cross section, the pattern of metamorphism is concentric about the intrusion.


Area behind the arc, which can be subject to compressional (causing thrusted mountain belts) or extensional (causing back-arc basins) forces.

back-arc basin

Depression formed behind an arc, where extension has caused a basin, typically with seafloor spreading.


Area of the shoreline that is always entirely above normal wave action.

banded iron formation

A sedimentary rock that formed long ago as free oxygen changed the solubility of iron, causing layers of iron rich and iron-poor sediments to form in thin layers, or bands.


A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.

bankfull stage

Largest amount of flow a river can hold before flooding.

barrier island

Ridges of sand, made from former beach sediments, that form parallel to the shoreline.

base level

Elevation of the mouth of a river.


A highly weathered soil deposit that consists of aluminum ores.

baymouth bar

A place where a spit extends out and covers a bay.

beach face

Active area of crashing waves.

beach replenishment

Adding sediment to a beach system in order to replace lost sediment due to longshore drift.


A specific layer of rock with identifiable properties.


Discernible layers of rock, typically from a sedimentary rock.


A specific type of sedimentary structure (ripples, plane beds, etc.) linked to a specific flow regime.


Sediment that large and dense, typically sits on the bottom of stream channels, and is only moved with higher-speed flows.


Ridge of sand built above the beach face.


Chemical sedimentary rocks that have a biologic component to their origin. Many limestones are biochemical.


The living things that inhabit the Earth.


Sedimentary layering disturbed by movement of organisms.

black smoker

Mineral chimneys that form at hydrothermal vents.


A metamorphic facies of low temperature, high pressure rocks, typified by the rock blueschist, a metamorphic rock containing a blue amphibole called glaucophane.

body wave

Seismic waves that travel through the Earth, mainly P waves and S waves.


Two or more atoms or ions that are connected chemically.

Bouma sequence

Predictable sequence of fining upward sediments, caused by turbidity flows.


Water that is a mixture of sea water and fresh water.

braided channel

Channel type with many switching channels, common with large sediment volumes.


Offshore durable structure designed to lessen wave action and reduce longshore drift.


A property of solids in which a force applied to an object causes the object to fracture, break, or snap. Most rocks, at low temperatures, are brittle.

burial metamorphism

Metamorphism that is caused by confining pressure and heat, both increasing with depth.

calcite compensation depth

Also known as the CCD, it is the point in the depths of the ocean where calcite start to dissolve, leaving only siliceous ooze behind.


An igneous composition or rock containing more than 50% carbonate minerals (e.g. calcite). Magma of this composition is very low temperature (500-600 C) relative to other magmas.

carbonic acid

An acid that forms from carbon dioxide and water. It is a large contributor to chemical weathering.


A type of breccia that forms in a brittle way within fault zones.


The idea that large, damaging events are the cause of most geologic events.


A positively-charged ion. In geology, this commonly includes ions of the elements Ca+2, Na+1, K+1, Fe+2,+3, Al+3, and Mg+2.


Sediment being "glued" together via mineralization, typically calcite and quartz from groundwater fluids.


A limestone made of coccolithophore shells, a type of single-celled algae.

chemical sedimentary

Sedimentary rocks that are precipitated, from solution.

chemical weathering

Breaking down of mineral material via chemical methods, like dissolution and oxidation.


A very fine grained version of silica deposited with or without microfossils.


Sedimentary rocks that are made of sediment, weathered pieces of bedrock.


A rock made primarily of clay.

closed basin

An internally draining watershed, whose waters do not flow to the ocean.


Former swamp-derived (plant) material that is part of the rock record.


The entire area which is related to land-sea interactions.


Forces that hold a substance together.


When two continents crash, with no subduction (and thus little to no volcanism), since each continent is to buoyant. Many of the largest mountain ranges and broadest zones of seismic activity come from collisions.


Sediment being squeezed together into a coherent mass.


The mineral make up of a rock, i.e. which minerals are found within a rock.


A mechanical process which takes ore and separates it from gangue material.

cone of depression

Area with a lower water table due to water pumping from a well.


Non-directional pressure resulting from burial.

confining layer

A layer that has lower permeability and porosity and does not allow fluid flow as easily.


A sedimentary rock with rounded, larger (≥2 mm) clasts.

connate water

Original water trapped inside a forming rock.

contact metamorphism

Metamorphism that occurs when rocks are next to a hot intrusion of magma.

continental crust

The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.

continental shelf

Submerged part of the continental mass, with a gentle slope.

continental slope

Steep part of an ocean basin that is the transition between the continental mass and the ocean floor.


The property of unevenly-heated (heated from one direction) fluids (like water, air, ductile solids) in which warmer, less dense parts within the fluid rise while cooler, denser parts sink. This typically creates convection cells: round loops of rising and sinking material.


Place where two plates come together, casing subduction or collision.


Limestone made of shell fragments cemented together.


The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components.


The stable interior part of a continent, typically more than a billion years old, and sometimes as old as  2.5-3 billion years. When exposed on the surface, a craton is called a shield.

crevasse splay

Sediment that breaks through a levée and deposits in a floodplain during a flood event

cross bed

A sedimentary structure that forms in the lower flow regime, where ridges of sediment form perpendicular to flow direction, but within the ridges, sediment layers and dips toward flow direction. Found in ripples and dunes. Can be tabular, sinuous, or trough shaped.


The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements. The crust has two types: continental, which is the thick, more ductile, and lowest density, and oceanic, which is higher density, more brittle, and thinner.


The part of the hydrosphere (water) that is frozen, found mainly at the poles.


The process of liquid rock freezing into solid rock. Because liquid rock is made of many components, the process is complex as different components freeze at different temperatures.

cut bank

Erosional part of a meandering channel.

debris flow

A mixture of coarse material and water, channeled and flowing downhill rapidly.

deductive reasoning

Taking known truths in order to develop new truths.


Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course.

dendritic drainage

A common branching style of drainage pattern.


Sediment gathering together and collecting, typically in a topographic low point.

depositional environment

An interpretation of the rock record which describes the cause of sedimentation (i.e. ancient beach, river, swamp, etc.).

deranged pattern

Drainages that are erratic and disappearing, typically in karst environments.

detachment fault

A style of low-angle, high extension normal faulting.


Sedimentary rocks made of mineral grains weathered as mechanical detritus of previous rocks, e.g. sand, gravel, etc.


Movement in a transform or strike-slip setting which it toward the right across the fault. As viewed across the fault, objects will move to the right.


Changes in sedimentary rocks due to increased (but low when compared to metamorphism) temperatures and pressures. This can include deposition of new minerals (e.g. limestone converting to dolomite) or dissolution of existing minerals.


A sedimentary rock containing two distinct grain sizes, typically cobbles (or larger) mixed with mud.

dip slip

Faulting that occurs with a vertical motion.

directed stress

Stress that has a strong directional component (unequal), typically creating elongated or flattened features.


Increased intensity due to being along the path of fault propagation.


Amount of water that leaves a system, such as a river or aquifer.


Two layered rocks that may seem conformable, but an erosional surface exist between them.


The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water).

dissolved load

Amount of material dissolved in stream water.


Place where two plates are moving apart, creating either a rift (continental lithosphere) or a mid-ocean ridge (oceanic lithosphere).

Doppler Effect

A change in wavelength and frequency of a wave due to the source of a wave moving relative to the observer of a wave.

drainage basin

The area within a topographic basin or drainage divide in which water collects.

drainage divide

Topographic prominence which sheds water into a specific drainage basin.

drainage pattern

The shape or form of a river and/or tributary drainage system.


A property of a solid, such that when a force is applied, the solid flows, stretches, or bends along with the force, instead of cracking or breaking. For example, many plastics are ductile.


A large pile of sediment, deposited perpendicular to flow. Internal bedding in dunes dips toward flow direction (i.e. cross bedding). Formed in the upper part of the lower flow regime.

Earth System Science

The study of the interaction of the spheres within the system that is the Earth, mainly the study of the hydrosphere, atmosphere, geosphere, and biosphere.


Plastic moving, fine-grained type of flow.

elastic rebound

A theory of building energy that is released during an earthquake.

electromagnetic spectrum

Visible light and its related energetic waves, including X-rays, UV rays, and radio waves.


A group of all atoms with a specific number of protons, having specific, universal, and unique properties.

emergent coastline

Features of a coastline where relative sea level is falling.

entrenched channel

A channel that carves into existing bedrock, preserving its original shape and character.

ephemeral stream

A stream or river that can be wet or dry depending on the season.


The location at the surface directly above the focus of an earthquake, typically associated with strong damage.


The transport and movement of weathered sediments.


Lagoon with brackish water, typically with abundant biologic factors.


A chemical sedimentary rock that forms as water evaporates.


A combination of evaporation and transpiration from plants, which is a measure of water entering the atmosphere.


A test of an idea in which new information can be gathered to either accept or reject a hypothesis.


A specific set of features that are tied together in an interpretive group. Facies can be based on mineralogy, biologic factors, fossils, rock types, etc.

failed rift arm

A section of a rift that starts but does not complete. This typically occurs at 120° angles to the active rift.

fair weather wave base

The depth normal, non-storm waves reach.


The idea that any claim in science can be proved wrong with proper evidence.


Planer feature where two blocks of bedrock move past each other via earthquakes.

fault scarp

Place where fault movement cuts the surface of the Earth.


Distance wind has been building a wave.


Extremely thin bedding in mudstones, a characteristic of shale.


Glacial valley filled by ocean water.


Flat area around a river channel that is filled with water during flooding events.

flow regime

A qualitative measure of the speed of a fluid flow, with different amounts of flow corresponding to different sedimentary structures, called bedforms. Typically, it is split into upper and lower flow regimes, with upper being a more rapid flow.

flower structure

A small area along a strike-slip or transform fault with branching structures of transpression/transtension, causing local hills or valleys.


Deposition that has to so with rivers.

flux melting

The process in which volatiles enter the mantle wedge, and the volatiles lower the melting temperature, causing volcanism.


Initiation point of an earthquake or fault movement.


A planer alignment of minerals and textures within a rock.


On a dipping fault, the part of the block that is below the fault. Moves down in normal faulting, up in reverse faulting.


Area in front of the arc, between the arc and the trench. Often marked by an accretionary wedge or a forearc basin.

forearc basin

Any depression formed between the arc and the trench, commonly between the arc and the accretionary wedge.


An earthquake that sometimes occurs before the larger mainshock.


Area between high tide and low tide.


An extensive, distinct, and mapped set of geologic layers.

fossil fuel

Energy resources (typically hydrocarbons) derived from ancient chemical energy preserved in the geologic record. Includes coal, oil, and natural gas.


Adjective for a rock filled with fossils, most commonly with limestones.


A process of injecting pressurized fluids into the ground to aid in hydrocarbon migration.

fracture zone

Faults along mid-ocean ridges that have a transform motion but do not produce earthquakes. These faults accommodate different amounts of movement along the mid-ocean ridge.


Material found around ore which is less valuable and needs to be removed in order to obtain ore.

geopetal structure

A feature in a rock that allows the observer to determine which direction was up in the past.


The solid, rocky parts of the Earth, including the crust, mantle, and core.


Deposition and erosion tied to glacier movement.




A very high grade metamorphic rock, higher grade than schist, with a separation of light and dark minerals.

Goldich Dissolution Series

Working opposite of Bowen's reaction series, it states that minerals that are formed at conditions more dissimilar to the surface are more quickly prone to chemical weathering.


A valley formed by normal faulting.


A qualitative measure of the amount of metamorphism that has occurred or the amount of a resource present in an ore.


Slope of a stream channel.


A sequence of layers in which the sediment changes linearly in size, either getting coarser or finer.

grain size

The average diameter of a grain of sediment, ranging from small, also known as fine-grained (e.g. clay, silt) to large, also known as coarse-grained (e.g. boulder).


A sandstone with a significant mud component OR a sandstone with a significant lithic fragment component.


Small jetties that help control longshore drift.


Water that is below the surface.

Groundwater mining

When discharge exceeds recharge, and the groundwater is withdrawn at a rate that depletes groundwater storage


An evaporite mineral, CaSo4•2H2O. Has one cleavage, hardness of 2. Typically clear or white.

half graben

A valley formed by normal faulting on just one side.

half life

The calculated amount of time that half of the mass of an original (parent) radioactive isotope breaks down into a new (daughter) isotope.


Also known as rock salt, or table salt. 3 cleavages at 90°, cubic crystal habit. Typically clear or white, hardness of 3.

hanging wall

On a dipping fault, the side that is on top of the fault plane. Moves down in normal faulting, up in reverse faulting.


The source of a river, the set of streams that feed into the river's beginning.


hopper crystal

Evaporites (like salt) which form cavities within rocks, which mimic the shape of the crystal.


A dense, hard metamorphic rock, typically derived from contact metamorphism.


Uplifted mountain block caused by normal faulting.

hot spot

Rising stationary magma, forming a succession of volcanism. This is reflected as islands on oceanic plates, and volcanic mountains or craters on land.

hummocky cross stratification

A special type of cross bedding that forms when strong storms produce mounds and divots of cross-bedded sand in deeper water.


Organic rich material found in soil.

hydraulic conductivity

The measure of how well a fluid flows through an object.


Water breaking into ions and replacing ions in minerals; a major type of chemical weathering in silicates.


The water part of the Earth, as a solid, liquid, or gas.


Metamorphism which occurs with hot fluids going within rocks, altering and changing the rocks.


A proposed explanation for an observation that can be tested.

igneous rock

Rocks that are formed from liquid rock, i.e. from volcanic processes.


Stacked cobbles in the direction of flow.


A piece of a rock that is caught up inside of another rock.

index mineral

Minerals that form at a specific range of temperatures and pressures. Using a collection of index minerals narrows down the conditions of rock formation.

induced seismicity

Earthquakes that occur due to human activity.

inductive reasoning

Establishing evidence (including new observations) to infer a possible truth.


Water that works its way down into the subsurface.

inner core

The innermost physical layer of the Earth, which is solid.


Period of warming within a glacial or ice age cycle.


A very brief period of warming, even warmer than a interglacial, within a glacial or ice age cycle.


An atom or molecule that has a charge (positive or negative) due to the loss or gain of electrons.

island arc

Place where oceanic-oceanic subduction causes volcanoes to form on an overriding oceanic plate, making a chain of active volcanoes.


An atom that has different number of neutrons but the same number of protons. While most properties are based on the number of protons in an element, isotopes can have subtle changes between them, including temperature fractionation and radioactivity.


Artificial device (typically a wall of concrete or rocks) placed to stop or slow longshore drift.


Carbonate rocks which dissolve, leaving behind caverns and holes which affect the landscape.


An ultramafic rock from deep volcanic vents that can contain diamonds.


Deposition in and around lakes.


Interior body of ocean water, at least partially cut off from the main ocean water.


Thin (less than 1 cm) beds of rock.


The measure of degrees north or south from the equator, which has a latitude of 0 degrees.  The Earth's north and south poles have latitudes of 90 degrees north and south, respectively.


Liquid rock on the surface of the Earth.

layered intrusion

Metallic mineral deposit consisting of mafic plutonic rocks, typically containing platinum-group elements, chromium, copper, nickel, etc.


A chemical or biochemical rock made of mainly calcite.


Linear alignment of minerals within a rock.


Process of saturated sediments becoming internally weak (like quicksand) and destabilizing foundations.


The process of turning sediment into a sedimentary rocks, including deposition, compaction, and cementation.


The outermost physical layer of the Earth, made of the entire crust and upper mantle. It is brittle and broken into a series of plates, and these plates move in various ways (relative to one another), causing the features of the theory of plate tectonics.


The beach (shoreline) zone, where waves are crashing.


Wind-blown silt, mainly formed from glacial processes.

longitudinal profile

Illustration of the topography of the base of a stream, showing zones of sediment production, transport, and deposition.

longshore current

A net movement that occurs as waves intersect the shoreline at non-perpendicular angles.

longshore drift

Sediment that moves via a longshore current.

Love wave

Surface waves that have a side-to-side motion.


Liquid rock within the Earth.

magnetic striping

Symmetric (about the ridge) patterns of magnetism created by ocean floor rocks recording changes in Earth's magnetic field.


A measure of earthquake strength. Scales include Richter and Moment.


Largest earthquake in an earthquake sequence.


Middle chemical layer of the Earth, made of mainly iron and magnesium silicates. It is generally denser than the crust (except for older oceanic crust) and less dense than the core.

mantle plume

Rising material and heat derived from the mantle. These may be responsible for hot spots.

mantle wedge

The area of the mantle where volatiles rise from the slab, causing flux melting and volcanism.


A metamorphosed limestone.


Places that are under ocean water at all times.

mass wasting

Any downhill movement of material, caused by gravity.

meander scar

Silted-in oxbow which still has a topographic expression.

meandering channel

Low-gradient channel where rivers sweep across broad flood plains.


Term for faulting that occurs in subduction.


Also called lower mantle, a solid, more brittle physical layer of the Earth, below the asthenosphere.


Minerals with a luster similar to metal and contain metals, including valuable elements like lead, zinc, copper, tin, etc.


Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. Metamorphism is the name of the process.

metamorphic facies

A specific set of index minerals tied to specific styles of metamorphism. When these minerals are present, it allows a history of metamorphism to be determined.

metamorphic rock

Rocks formed via heat and pressure which change the minerals within the rock.


Limestone made of primarily fine-grained calcite mud. Microscopic fossils are commonly present.

mid-ocean ridge

A divergent boundary within an oceanic plate, where new lithosphere and crust is created as the two plates spread apart. Mid-ocean ridge and spreading center are synonyms.


A rock transitional between metamorphic and igneous rock, i.e. rocks so metamorphosed that they begin the process of melting.


Place where material is extracted from the Earth for human use.


A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.


A mineral-like substance that does not meet all the criteria as a true mineral. Examples include glass, coal, opal, and obsidian.

Mississippi Valley-type

Metallic mineral deposit of mainly lead and zinc from groundwater movements within sedimentary rocks.

Modified Mercalli Intensity Scale

A qualitative earthquake scale, from I-XII, of the degree of shaking in an earthquake.


Short for Mohorovičić Discontinuity, it is the seismically-recognized layer within the Earth in which the crust ends and the mantle begins. Because the crust is very different in composition to the mantle, the moho is easy to find, since seismic waves travel differently through the two materials.

Moment magnitude

A magnitude scale based on calculation of the energy released in an earthquake.


The end of a river out of which water flows into a sea or other large body of water.


mud chip

Pieces of mudcracks that are incorporated into a sedimentary rock.


Polygonal cracking that occurs with shrinking clays. Indicative of mud submerged underwater and then exposed to air.


A rock made of primarily mud, i.e. particles smaller than sand (≤0.064 mm).


Fault-formed rock via ductile deformation, deeper within the Earth.

natural gas

Gaseous fossil fuel derived from petroleum, mostly made of methane.

natural hazard

A significant and dangerous event that is part of a natural process.

natural levée

Built-up area around a river channel which can hold river flow within a channel.

natural resources

Items that are found within Earth that are valuable and limited. Examples include coal, water, and gold.


Shore area between low tide and storm wave base. Upper part is dominated by fair weather wave base, lower part is dominated by storm wave base.


Metamorphic textures that do not have a directional component of its minerals.


Layered rocks on top of a non-layered rock, such as crystalline basement.


Minerals that have a luster that is not similar to metal, and typically do not contain valuable metals like copper, lead, zinc, tin, etc.

nonpoint source

Pollution that does not come from one specific, known place, but instead, comes from a wide, broad zone.


A resource that is not able to be replaced on human time scales.

normal fault

A dip-slip fault in which the hanging wall drops relative to the footwall, caused by extensional forces.

normal force

Component of the gravitational force which holds material on a slope.


Process which allows a continental plate to bring up oceanic plate, frequently occurring in collision zones.


An observation that is completely free of bias, i.e. anyone and everyone would make the same observation.


The act of gathering new information from the senses or from a scientific instrument.

oceanic crust

The thin, outer layer of the Earth which makes up the rocky bottom of the ocean basins. It is made of rocks similar to basalt, and as it cools, even become more dense than the upper mantle below.

oceanic-continental subduction

Where an ocean plate subducts beneath a continental plate, causing a volcanic arc to form.

oceanic-oceanic subduction

Where a dense ocean plate subducts beneath a less dense oceanic plate, causing an island arc to form.

octet rule

A rule that says the outer valence shell of electrons is complete when it contains 8 electrons.


Amount of movement during a faulting event.


The part of the coastline which is below any wave base action.


A dark liquid fossil fuel derived from petroleum.

oil shale

Oil which is found in low-permeability, high-porosity rocks such as shale.


(Fe,Mg)2SiO4. Typically translucent olive green and equant, with no cleavage. Common in mafic igneous rocks and in the mantle, but easily weathered in surface conditions. Structure is isolated silica tetrahedra. Known as peridot when a gem.


Spheres of calcite that form in saline waters with slight wave agitation. Ooid refers to the sphere, oolite the rock with the spheres.

open pit mine

Large surface mine with opening carved into the ground.


Rocks of the ocean floor, such as mid-ocean ridge rocks, which are brought to the surface.


Valuable material in the Earth, typically used for metallic mineral resources.

ore mineral reserve

A proven commodity of profitable material that could be mined.

ore mineral resource

Potentially extractible and valuable material, but unproven.


The process of uplifting mountain within mountain belts, primarily via tectonic movement. Orogenic belts are the mountain belts that result from these movements, and orogenesis is the name for the process of forming mountain belts.

outer core

The outer physical layer of the core, which is liquid. Movement within the outer core is believed to be responsible for Earth's magnetic field and flips of the magnetic field.


A slope, that by natural or human activity, becomes steeper than the angle of repose.


Abandoned meanders that are cut off from the main channel.


Certain metallic elements (like iron) take in oxygen, causing reactions like rust.

p wave

The fastest seismic wave that occurs after an earthquake, compressional in nature.


Direction of flow preserved in the rock record.


As a rock cools, the iron minerals within the rock align with the current magnetic field. Since the magnetic field changes (by where you are on Earth, by flips where "north"and "south" switch, and by migration of the magnetic north pole), scientists use the magnetic alignment within rocks to determine past movement or the magnetic field itself, along with the movement of rocks and plates via plate tectonics.


Deposition in swamps.


The most recent supercontinent, which formed over 300 million years ago and started breaking apart less than 200 million years ago. Africa and South America, as well as Europe and North America, bordered each other.

parent isotope

A radioactive atom that can and will decay.

parting lineation

Subtle ridges formed in the upper flow regime on top of plane beds in the direction of flow.

passive margin

A boundary between continental and oceanic plates that has no relative movement, making it a place where an oceanic plate is connected to a continental plate, but it is not a plate boundary.

peer review

A process where experts in a field review and comment on a newly-introduced work, typically a part of publication.


An intrusive ultramafic rock, which is the main component of the mantle. The minerals in peridotite are typically olivine with some pyroxene.


The ability for a fluid to travel between pores, or, how connected the pores are within a rock or sediment.


A fossil fuel derived from shallow marine rocks. Consists of oil and natural gas.

phase diagram

Chart that show the stability of different phases of a substance at different conditions.


A rock more metamorphosed than slate, to the point that microscopic (but larger) mica gives the rock a glow, called a sheen. Crenulation, or small bends/folds in the foliation can be present.

piercing point

An object that is cut by a fault which allows the amount of movement to be determined. This is useful for all faults, but more commonly used in strike-slip faults.


Deposit of heavy ores in stream or beach sediments.

plane bed

A specific layer of rock formed by flowing fluid, either in the lowest part of the lower flow regime or lower part of the upper flow regime.


A solid part of the lithosphere which moves as a unit, i.e. the entire plate generally moves the same direction at the same speed.

plate boundary

Location where two plates are in contact, allowing a relative motion between the two plates. These are the locations where most earthquakes and volcanoes are found.

Plate tectonics

The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.


A dry lake bed in a desert valley.

point bar

Depositional portion of a meandering channel.

point source

Pollution that comes from one known source.


A molecule (like water) which has a positive side and a negative side.


Minerals with the same composition and different crystal structures


A specific chemical composition that forms different minerals and different temperatures and pressures. Quartz has several different polymorphs, including coesite, tridimite, and stishovite.


Empty space in a geologic material, either within sediments, or within rocks. Can be filled by air, water, or hydrocarbons.


Amount of empty space within a rock or sediment, including space between grains, fractures, or voids.


Large metallic mineral deposit that forms near magma bodies like plutons. Commonly contains copper, lead, zinc, molybdenum, and gold.

potentiometric surface

The height of the water table, if no confining layers or other hinderances present.


The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.

Principle of Cross-Cutting Relationships

A geologic object can not be altered until it exists, meaning, the change to the object must be younger than the object itself.

Principle of Faunal Succession

The fossils found at any time are unique, and the fossils in layers of different ages have progressed and changed as time has moved forward. Fossils found in layers that are not as old have organisms that more resemble organisms that are alive today.

Principle of Lateral Continuity

Layered rocks can be assumed to continue if interrupted within its area of deposition.

Principle of Original Horizontality

Layered rocks are generally laid down flat at their formation.

Principle of Superposition

In an undisturbed sequence of strata, the rocks on the bottom are older than the rocks on the top.

Principle of Uniformitarianism

Idea championed by James Hutton that the present is the key to the past, meaning the physical laws and processes that existed and operate in the past still exist and operate today.


The rocks that existed before the changes that lead to a metamorphic rock, i.e. what rock would exist if the metamorphism was reversed.


The study of the components of a rock, mainly sedimentary rocks, and the information that can be obtained by understanding the origin of the components.

proxy indicator

A measurement which can specify a change in another system. For example, changes in climate can change the amount of certain isotopes of oxygen and carbon in sea creatures.


A method of investigation the claims to be scientific, but does not hold up to full scientific scrutiny. Examples include astrology, paranormal studies, young-Earth creationism, and cryptozoology (i.e. the study of creatures like Bigfoot and the Loch Ness Monster).


XY(Al,Si)2O6, in which X typically equals Na, Ca, Mg, or Fe and Y typically equals Mg, Fe, or Al. Typically black to dark green, blocky, with two cleavages at ~90°. Common in mafic igneous rocks and some metamorphic rocks. Structure is a single chain of silica tetrahedra.


An observation which is based on non-numerical data. While these types of observations are not preferred, they can still be useful.


An observation which is based on numerical data. These observations are preferred because they can be used in calculations.


A metamorphosed sandstone.

radial drainage

Drainage pattern emanating from a high point.


The process of atoms breaking down randomly and spontaneously.

raindrop impression

Small circular pits formed by raindrops impacting soft sediments.

Rayleigh wave

Surface waves that have a up and down motion.


Area where water infiltrates into the ground and adds to the overall groundwater.


The process of changing a mineral without melting.


Average time between earthquakes calculated based on past earthquake records.


Reactions that are related to the availability of oxygen. Many minerals or ions change their solubility based on redox conditions.


A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals.


Removing trace elements from desired elements.


Waves that bounce off of a boundary between mediums of different properties.


Waves that change direction due to changing speeds, typically caused by a change in density of the medium.

regional metamorphism

Metamorphism that occurs with large-scale tectonic processes, like collision zones.


Loose material that is a mixture of soil components and weathered bedrock sediments.


Sea level fall over time.

relative dating

Determining a qualitative age of a geologic item in relation to another geologic item.


The process of cleaning up a polluted site.


A resource which is replaced on human time scales.


Rocks which allow petroleum resources to collect or move.


An amplification of earthquake waves due to a structure of buildings or structures.

retangular drainage

Drainage pattern in an area of low topography, dominated by bedding planes, joints, and fracture patterns.

reverse fault

A dip-slip fault that has the hanging wall moving up with respect to the foot wall.


Root systems preserved in rocks.

Richter scale

A magnitude scale using the amplitude of shaking via a seismograph.


Area of extended continental lithosphere, forming a depression. Rifts can be narrow (focused in one place) or broad (spread out over a large area with many faults).

rip current

Currents that push seaward.


Ridges of sediment that form perpendicular to flow in the lower part of the lower flow regime.

rock cycle

The process of changing rocks on Earth into different forms, namely igneous, sedimentary, and metamorphic.

rock fall

Detached, free-falling rocks from very steep slopes.

rotational slide

Movement of regolith along a curved slip plane.


How smooth or rough the edges are within a sediment.


Water that flows over the surface.

s wave

Second-fastest seismic wave that has a sheer motion.


A rock primarily made of sand.


A solution that has the maximum allowed dissolved component, and is unable to dissolve more.


Rock more metamorphosed than phyllite, to the point that mica grains are visible. Larger porphyroblasts are sometimes present.


Term for coarse grained, visible, platy minerals in a planar fabric, typical of schists.

science denial

The act of purposely ignoring or dissenting from science for political or cultural gains.

scientific method

The idea in science that phenomena and ideas need to be scrutinized using hypothesizing, experimentation, and analysis. This can eventually result in a consensus or scientific theory.


An eroded island. Since wave and weather action does not extend deep into the ocean, the root of the island is preserved as a seamount. Reefs can grow around seamounts.

sediment-hosted copper

Diagenetic copper deposit within sedimentary rocks.

sediment-hosted disseminated gold

Low grade, broad deposits of microscopic gold found in sedimentary rocks with diagenetic alteration.

sedimentary rock

Rocks that are formed by sedimentary processes, including sediments lithifying and precipitation from solution.


Pieces of rock that have been weathered and possibly eroded.

seismic anomoly

Areas that have an unpredicted change in seismic data, indicating a change in properties.

seismic gap

Length of fault without earthquake activity, due to a locked segment of a fault.

seismic wave

Energy that radiates from fault movement via earthquakes.


Instrument used to measure seismic energy.

sequence stratigraphy

The study of changes in the rock record caused by changing sea level over time.


Rock formed from hydrothermal alteration of basalt, made of serpentine.


A very fine-grained rock with very thin layering (fissile).

shear force

Component of the gravitational force which pushes material downslope.

shear strength

The relationship between shear force and normal force in a block of material on a slope. When shear force is greater than normal force, mass wasting can occur.

shock metamorphism

Metamorphism caused by bolide impacts.


Part of the coastal depositional environment, near the tidal zone but below. Lower shoreface is the part of the coastline which is only disturbed by storm waves, upper shoreface is disturbed by typical, daily wave action.


The part of the coastline which is directly related to water-land interaction, specifically the tidal zone and the range of wave base.


Mineral group in which the silica tetrahedra, SiO4-4, is the building block.

silicon-oxygen tetrahedra

A anion structure of one silicon bonded to four oxygens, in the shape of a tetrahedron, with the silicon in the center and four oxygens at the corners of the structure. It has a net charge of -4, and can bond to cations to form silicate minerals.


A rock made of primarily silt.


A strike-slip or transform motion in which the relative motion is to the left. As viewed across the fault, objects will move to the left.


Carbonate rock that reacts with hot magmatic fluids, creating concentrated ore deposits, which include copper, iron, zinc, and gold.


Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism.


Metamorphic rock with a strong foliation but no visible minerals, derived from mudstones or shales.

slaty cleavage

A microscopic foliation in slate, in which flat slabs and planes of rock develop.


A polished surface of rock from fault movement, covered with groves.


A process which chemically separates desired element(s) from ore minerals.

soft sediment deformation

Weak, typically saturated sediments that deform and contort before lithification.

soil creep

Very slow movement of the soil downhill.

soil horizon

Specific layers within a soil profile with specific properties.

soil profile

A hypothetical or real section cut through soil, showing the different layers (horizons) that exist.

sole mark

A series of sedimentary structures formed on the base of a flow, eroding into underlying sediment. Examples include scour marks, flute casts, groove casts, and tool marks.

solid solution

Two or more elements that can easily substitute for each other, due to similarities in ionic size and charge.


The act of taking a solid and dissolving it into a liquid. This commonly occurs with salts and other minerals in water.


An acronym for SOund Navigation And Ranging, sonar uses sound waves to navigate and map surfaces.  Sound waves created by an observer reflect off of surfaces and return to the observer.  The amount of time it takes for the sound to return is a function of the distance the surface is from the observer.  Bats use sonar to navigate through the dark.  Ships use sonar to map the ocean floor.


The range of sediment sizes within a sediment or sediment within sedimentary rocks. Well sorted means the sediment has the same sizes, poorly sorted means many different sizes are present.

source rock

A rock that contains material which can be turned into petroleum resources. Organic-rich muds form good source rocks.


The study of the details of light, which can tell you the chemical makeup of light and even the movement of a light source.


A ridge of sediment that occurs out into a body of water, formed via longshore currents.


A place where pressurized groundwater flows onto the surface.


Rock spire that is offshore and a remnant of a rock layer.

storm wave base

The depth that waves can reach in large storms, such as hurricanes.

straight channel

Channels that form straight, typically near the headwaters.


The deformation that results from application of a stress.


The study of rock layers and their relationships to each other within a specific area.


A channelled body of water.


Force applied to an object, typically dealing with forces within the Earth.

strike slip

Faulting that occurs with shear forces, typically on vertical fault plaines as two fault blocks slide past each other.

strip mine

Mining that occurs as entire layers of ore and gangue are removed.


Large and mysterious landslides that travel for long distances.


A process where an oceanic plate descends bellow a less dense plate, causing the removal of the plate from the surface. Subduction causes the largest earthquakes possible, as the subducting plate can lock as it goes down. Volcanism is also caused as the plate releases volatiles into the mantle, causing melting.

subduction zone metamorphism

Metamorphism that occurs in subduction zones, typically lower temperature and higher pressure.


An observation which is influenced by the observer's personal bias.

submarine canyon

Canyon carved into a continental shelf.

submarine fan

Broad cone of coarse sediment deposited from a submarine flow or turbidity flow.

submergent coastline

Features of a coastline where relative sea level is rising.


Lower layer of the soil (B) which is a mixture of weathered bedrock, leeched materials, and organic material. Has two sublayers: the upper part, or regolith (with more organic materials), and the lower part, saprolite, which is only slightly weathered bedrock.


Lowest layer of the soil (C), which is mechanically weathered (not chemically weathered) bedrock.

summer berm

Lower, seaward berm that forms with lower wave energy in summer months.


An arrangement of many continental masses collided together into one larger mass. According to the Wilson Cycle, this occurs every half billion years or so.

superfund site

A federally-supported pollution clean-up effort.

supergene enrichment

Oxidation that occurs in sulfide deposits which can concentrate valuable elements like copper.

surf zone

Shoreline area of breaking waves.

surface mine

Mining that occurs near the Earth's surface.

surface wave

Seismic waves that only move along the surface, mainly R waves and L waves.

suspended load

Bedload sediments that can be carried by higher-velocity flows.


An interconnected set of parts that combine and make up a whole.


Rounded cavities within rocks that form in various ways, including mineral growth, mainly salt.


Loose blocks of rock that fall down from steep surfaces and cover slopes.

tar sand

Sands or sandstones that contain high-viscosity petroleum.


The measure of the vibrational (kinetic) energy of a substance.


An elevated erosional surface caused by glacial or fluvial action.


A geological province which is added (accreted) to a continental mass via subduction and collision.


Depositional environments that are on land.


Arrangement of minerals within a rock.


Deepest part of a meandering channel.


An accepted scientific idea that explains a process using the best available information.


Faulting that is deep into the crust, and typically involves crystalline basement rocks.


Faulting that is not deep into the crust, and typically only involves sedimentary cover, not basement rocks.

thrust fault

A low-angle reverse fault, common in mountain building.

tidal flat

Wide and flat area of land covered by ocean water during high tide, but exposed to air by low tide.


General term for very poorly sorted sediment that is of glacial origin.


Sand bar that connects a stack and the shore.


A process of using 3D seismic arrays to get subsurface images.


Upper layer of soil, made mainly out of organic material.


Place where two plates slide past each other, creating strike slip faults.


Sea level rise over time.

translational slide

A landslide that moves a long an internal plane of weakness.


A segment along a transform or strike-slip fault which has a compressional component, sometimes creating related thrust faulting and mountains.


A place along a transform or strike-slip fault with an extensional component, sometimes including normal faulting, basin formation, and volcanism.


A geologic circumstance (such as a fold, fault, change in lithology, etc.) which allows petroleum resources to collect.


Porous, concentric, or layered variety of carbonate that forms with often heated water in springs and/or caves.

trellis drainage

A drainage pattern which forms between ridge lines in deformed (typically sedimentary) rocks.


Deepest part of the ocean where a subducting plate dives below the overriding plate.


A natural water stream that flows into a larger river or other body of water.



An event that causes a landslide event. Water is a common trigger.

triple junction

Place where three plate boundaries (typically divergent) extend from a single point at 120° angles.


Formally known as a tidal wave, it is a large wave produced from a sudden movement of the floor of a ocean basin, caused by events such as earthquakes, volcanic eruptions, landslides, and bolide impacts.


Porous variety of carbonate that form in relatively unheated water, sometimes as towers and spires.


Turbidite is the rock that forms from a turbidity flow, a relatively coarse and dense sediment transported to the abyssal plain.

turbidity current

Dense flow of sediment that goes down submarine canyons, forming submarine fans and turbidites.


Missing time in the rock record, either because of a lack of deposition and/or erosion.

underground mine

Mining that occurs within tunnels and shafts inside the Earth.

universal solvent

A chemical that can dissolve a wide range of other chemicals.

vadose zone

Place where pores are filled with some water and some air, above the water table.


A type of lamination that is cyclical, perhaps seasonal or diurnal.


The resistance of a fluid to flow, where a high value means a fluid which does not like to flow (like toothpaste), and a low value means a fluid which flows easily (like water).


Components of magma which are dissolved until it reaches the surface, where they expand. Examples include water and carbon dioxide. Volatiles also cause flux melting in the mantle, causing volcanism.

volcanic arc

Place with a chain of mountain volcanism on a continent, from oceanic-continental subduction.

volcanogenic massive sulfide

Metallic mineral deposit which forms near mid-ocean ridges.

Wadati-Benioff zone

A zone of earthquakes that descend into the Earth with the subducting slab. This is commonly used as evidence for plate tectonics.

water right

A purchase or claim to a legal allotment of a water source, obtained through the state government, such as a spring, stream, well, or lake.

water table

The part of the groundwater system which has pore space 100% filled with water.

wave base

The depth in which the movement of waves can be felt, specifically by sediments. This is approximately equal to 1/2 the wavelength. Wave base can change depending on fair weather verses stormy weather.

wave crest

Top of a wave.

wave cut platform

Flat erosional surface cut by wave action.

wave height

Twice the amplitude, or, the distance between the crest and trough of a wave.

wave notch

Erosional notch in bedrock cut by waves.

wave period

The time between like parts of a wave passing a fixed point.

wave train

A series of waves that form and move as a group.

wave trough

Bottommost part of a wave.

wave velocity

Speed at which a wave travels past a fixed point.


The distance between any two repeating portions of a wave (e.g., two successive wave crests).


Breaking down rocks into small pieces by chemical or mechanical means.

Wilson Cycle

The cycle of opening ocean basins with rifting and seafloor spreading, then closing the basin via subduction and collision, creating a supercontinent.

winter berm

Higher, landward berm that forms with higher wave energy in winter months.


A piece of foreign rock that has been incorporated into a magma body. This can be a different type of magma, or a mantle xenolith, a rock from the mantle brought up near the surface.

yazoo stream

A tributary that runs parallel to a main stream within the floodplain.


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An Introduction to Geology Copyright © 2017 by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, Cam Mosher is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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