Glossary
A comprehensive reference guide for geology terms and definitions. Search for specific terms or browse alphabetically.
Ablation
The loss of ice or snow from a glacier or ice sheet through melting, sublimation, or other processes. Ablation is the opposite of accumulation.
Acisol
A type of acidic soil with low base saturation, typically found in tropical and subtropical regions. Often requires nutrient supplements for agriculture.
Amphibolite
A metamorphic rock composed primarily of amphibole minerals. Forms from metamorphism of igneous rocks under conditions of moderate pressure and temperature.
Anticline
An upward-arching fold in rock layers. The oldest rocks are found in the center of an anticline. Often forms traps for oil and natural gas.
Aquifer
A porous rock unit that can store and transmit groundwater. Important water source for wells and springs. Porosity and permeability are key properties.
Asthenosphere
The partially molten upper mantle layer beneath the lithosphere on which tectonic plates move. Enables plate tectonics. Low-velocity zone for seismic waves.
Basalt
A dark, fine-grained igneous rock formed from lava. The most common volcanic rock. Makes up most of the oceanic crust.
Batholith
A large underground body of igneous rock that cooled from magma. Forms from intrusion and solidification at depth. Often exposed after overlying rocks erode.
Bedding
The layers visible in sedimentary rocks. Represents successive depositional episodes. Important for understanding depositional environments and history.
Calcite
A common mineral (CaCO₃) that forms limestone and marble. Reacts with dilute hydrochloric acid. Often contains fossils. Used in cement and agriculture.
Cleavage
The tendency of minerals to break along planes of weakness in their crystal structure. Perfect cleavage produces smooth, shiny surfaces. Important for mineral identification.
Convergent Boundary
A plate boundary where two tectonic plates move toward each other. Results in subduction, collision, and mountain building. Associated with earthquakes and volcanoes.
Deposition
The process by which sediment is laid down. Occurs when the transporting agent (water, wind, ice) loses energy. Forms sedimentary rock over geological time.
Dolomite
A mineral (CaMg(CO₃)₂) and rock type similar to limestone. Does not react as vigorously with acid as calcite. Sometimes called dolostone when referring to the rock.
Earthquake
Sudden release of energy from movement along faults or plate boundaries, causing ground shaking. Measured by magnitude (energy) and intensity (effects). Most common at plate boundaries.
Erosion
The removal and transport of weathered material by water, wind, ice, or gravity. Key process in landscape evolution and sediment production.
Feldspar
The most abundant mineral in Earth's crust. Silicate mineral containing aluminum and other elements. Important component of igneous and metamorphic rocks.
Fold
A bend in rock layers caused by deformation. Anticlines and synclines are the main types. Indicative of compressive forces at plate boundaries.
Fossil
The preserved remains or traces of ancient organisms found in rocks. Crucial for understanding Earth's history and correlation of rock layers.
Granite
A light-colored, coarse-grained igneous rock composed of quartz, feldspar, and mica. Forms from slow cooling of magma at depth. Makes up most continental crust.
Gravel
Unconsolidated sediment consisting of rounded or angular rock fragments larger than sand (>2 mm). Often found in riverbeds and glacial deposits.
Hydrothermal
Related to hot water, especially heated groundwater. Hydrothermal solutions carry dissolved minerals and can form ore deposits and geysers.
Igneous
Rocks formed from the cooling and solidification of magma or lava. Can be intrusive (forms underground) or extrusive (forms above ground).
Index Fossil
A fossil that is distinctive, abundant, and wide-ranging geographically. Useful for dating and correlating rock layers from different locations.
Intrusion
An igneous rock body that formed from magma solidifying beneath the surface. Examples include batholiths, sills, and dikes.
Joint
A fracture in rock along which there has been no significant displacement. Differs from a fault. Important for weathering and groundwater movement.
Landslide
Rapid downslope movement of rock, soil, and debris. Common natural hazard in mountainous terrain. Can be triggered by earthquakes or heavy rainfall.
Lava
Molten rock material that erupts from a volcano. Solidifies to form extrusive igneous rock. Temperature typically 700-1200°C.
Limestone
A sedimentary rock composed primarily of calcite. Often contains fossils. Can be formed from shell fragments or chemical precipitation.
Lithosphere
The rigid outer layer of Earth comprising the crust and upper mantle. Divided into tectonic plates that move across the asthenosphere.
Magma
Molten rock material beneath Earth's surface. Becomes lava when it erupts. Source of igneous rocks. Temperature typically 700-1200°C.
Metamorphic
Rocks formed when existing rocks are transformed by heat, pressure, or chemical processes, usually at depth. No melting occurs.
Mineral
A naturally occurring, inorganic solid with definite chemical composition and ordered crystal structure. Building blocks of rocks.
Mohs Scale
A scale of mineral hardness from 1 (softest, talc) to 10 (hardest, diamond). Used to identify minerals by their hardness relative to standard minerals.
Quartz
The second most abundant mineral in Earth's crust (SiO₂). Hard, transparent or translucent. Common in igneous, metamorphic, and sedimentary rocks.
Sedimentary
Rocks formed from compaction and cementation of sediment. Often contain fossils. Include sandstone, shale, and limestone.
Stratum (Strata)
A distinct layer of rock or soil. Multiple layers are called strata. Fundamental unit in stratigraphy and understanding Earth's history.
Syncline
A downward-arching fold in rock layers. The youngest rocks are found in the center. Opposite of an anticline.
Tectonic Plates
Large rigid sections of Earth's lithosphere that move across the asthenosphere. Interactions at plate boundaries cause earthquakes, volcanoes, and mountains.
Unconformity
A surface of erosion or non-deposition representing missing time in the rock record. Indicates a gap in geological history at that location.
Volcano
An opening in Earth's crust where molten rock, gases, and solid material erupt. Can be shield, composite, or cinder cone types.
Weathering
The breakdown of rocks in place through mechanical, chemical, or biological processes. Produces sediment and alters rock composition.
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