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Glossary of Geology Terms
- Asthenosphere
- Portion of the mantle beneath the lithosphere composed of partially melted material.
- Batholith
- A large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the Earth's crust.
- Brackish
- Containing a mixture of seawater and fresh water.
- Caldera
- A large crater formed by volcanic explosion or by collapse of a volcanic cone.
- Clastic
- Made up of fragments of preexisting rock.
- Convection Current
- Circular movement of a fluid in response to alternating heating and cooling.
- Convergence
- The movement of two plates toward one another.
- Crust
- Thin, solid outer portion of Earth.
- Diagenesis
- The process of chemical and physical change in deposited sediment during its conversion to rock.
- Dike
- A long mass of minerals, usually an intrusion of igneous rocks, filling up rents or fissures in the original strata.
- Divergence
- Separation of two plates as they move in opposing directions.
- Extrusive
- Mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.
- Granoblastic
- An anhedral phaneritic equi-granular metamorphic rock texture.
- Heterogeneous
- Consisting of a diverse range of different items.
- Holocrystalline
- Completely crystalline said of a rock like granite, all the constituents of which are crystalline.
- Homogeneous
- Being the same throughout
- Hypocrystalline
- Partly crystalline said of rock which consists of crystals embedded in a glassy ground mass.
- Intrusion
- Body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto, the Roman god of the underworld.
- Laccolith
- An igneous intrusion that has been injected between two layers of sedimentary rock.
- Lacustrine
- Of or relating to lakes.
- Lithosphere
- Rigid uppermost section of the mantle combined with the crust.
- Mantle
- Thick, dense layer of rock that underlies Earth's crust.
- Metamorphism
- The solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids without melting.
- Metasomatic
- The process by which the chemical composition of a rock is changed by interaction with fluids; replacement of one mineral by another without melting.
- Moraine
- An accumulation of boulders, stones, or other debris carried and deposited by a glacier.
- Ocean Trench
- Deep depression in the seafloor, created by an oceanic plate being forced downward into the subsurface by another, overriding plate.
- Phenocryst
- Large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock.
- Plate Margin
- The boundaries where plates meet.
- Plate Tectonics
- See this website describing the movement of plates.
- Plates
- Large regions of Earth's surface, composed of the crust and uppermost mantle, which move about, forming many of Earth's major geologic surface features.
- Pluton
- An intrusive igneous rock body that crystallized from a magma below the surface of the Earth.
- Porphyritic
- Igneous texture consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. The larger crystals are called phenocrysts.
- Schistose
- Of or pertaining to schist; having the structure of a schist.
- Seafloor Spreading
- Process in which new seafloor forms as molten rock from Earth's interior rises toward the surface, pushing the existing seafloor out of its way.
- Sill
- A tabular mass of igneous rock that has been intruded laterally between layers of older rock.
- Stratification
- Formation or deposition of layers, as of rock or sediments.
- Subduction
- Tectonic process that involves one plate being forced down into the mantle at an oceanic trench, where it eventually undergoes partial melting.
- Transform Motion
- Horizontal plate movement in which one plate slides past another.
- Viscous
- Measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as "thickness", or resistance to flow.
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ECOS is supported by the GK-12 Program of the National Science Foundation.