ESC Chapter 4
Terms
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- Basalt
- A fine-grained, dark, mafic igneous rock composed largely of plagioclase feldspar and pyroxene. The extrusive equivalent of gabbro.
- Batholith
- A great irregular mass of coarse-grained igneous rock that covers at least 100 square km; the largest pluton
- Concordant intrusion
- An intrusive igneous rock whose boundaries lie parallel to the layers of preexisting bedded rock.
- Country rock
- The rock surrounding an intrusive igneous rock
- Dacite
- A light-colored, fine grained extrusive igneous rock with the same general composition as andesite. The extrusive equivalent of granodiorite.
- Decompression Melting
- Melting that occurs when mantle material rises to an area of lower pressure at a mid-ocean ridge. As the mantle material rises and the pressure decreases below a critical point, solid rocks melt spontaneously without the introduction of any additional hea
- Dike
- A tabular igneous intrusion that cuts across layers of bedding in country rock.
- Diorite
- A coarse-grained, intrusive igneous rock with composition intermediate between granite and gabbro. The intrusive equivalent of andesite.
- Discordant intrusion
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An intrusive igneous rock that cuts across the layers of the country rock that it intrudes
- Extrusive igneous rock
- A fine-grained or glassy igneous rock formed from a rapidly cooling magma that eurpts at the surface through a volcano.
- Felsic rock
- A light-colored, igneous rock that is poor in iron and magnesium and rich in high-silica minerals such as quartz, orthoclase feldspar and plagioclase feldspar.
- Fluid-induced melting
- Melting that takes place when water-laden sediments on a subducting oceanic plate are carried doward into a subduction zone. The increase in pressure squeezes water out of the minerals in the outer layers of the descending slab. The water rises buoyantly
- Fractional crystallization
- The process by which the crystals formed in a cooling magma are segregated from the remaining liquid at progressively lower temperatures.
- Gabbro
- A dark gray, coarse-grained intrusive igneous rock with an abundance of mafic minerals, particularly pyroxene. The intrusive equivalent of basalt.
- Granite
- A felsic, coarse-grained, intrusive igneous rock composed of quartz, orthoclase feldspar, sodium-rich plagioclase feldspar and micas. The intrusive equivalent of rhyolite.
- Granodiorite
- A light-colored, coarse-grained intrusive igenous rock similar to granite in having abundant quartz, but whose predominant feldspar is plagioclase, not orthoclase. The intrusive equivalent of dacite.
- Hydrothermal Vein
- A vein filled with minerals that contain large amounts of chemically bound water and are known to crystallize from hot-water solutions.
- Intermediate Igneous Rock
- An igneous rock midway in composition between mafic and felsic, neither as rich in silica as the felsic rocks nor as poor in it as the mafic rocks.
- Intrusive igneous rock
- A coarse-grained igneous rock that crystallized slowly when magma intruded into country rock deep in Earth's crust.
- Mafic Rock
- A dark-colored, igneous rock containing minerals (such as pyroxene and olivine) rich in iron and magnesium and relativel poor in silica.
- Magma Chamber
- A magma-filled cavity in the lithosphere that forms as ascending drops of melted rock push aside surrounding solid rock.
- Magmatic Differentiation
- A process by which rocks of varying composition can arise from a uniform parent magma. Various minerals crystallize at different temperatures, and the composition of the magma changes as it is depleted of the chemical elements withdrawn to make the crysta
- Obsidian
- A dense, dark, glassy volcanic rock, usually of felsic composition.
- Ophiolite suite
- An unusual assemblage of rocks, characteristic of the seafloor but found on land, consisting of deep-sea sediments, submarine basaltic lavas, and mafic igneous intrusions. The assemblage comprises fragments of oceanic crust that were transported by seaflo
- Partial melting
- The incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures.
- Pegmatite
- A vein of extremely coarse grained granite, crystallized from a water-rich magma in the late stages of solidification, that cuts across a much finer grained country rock. Pegmatites provide ores of many rare elements, such as lithium and beryllium.
- Peridotite
- A coarse-grained ultramafic intrusive igneous rock composed of olivine with small amounts of pyroxene and amphibole. The dominant rock in Earth's mantle and the source rock of basaltic melts.
- Pluton
- A large igneous intrusion ranging in size from a cubic kilometer to hundreds of cubic kilometers, formed at depth in the crust.
- Porphyry
- A lava of mixed texture in which large crystals (phenocrysts) "float" in a predominantly fine crystalline matrix.
- Pumice
- A frothy mass of volcanic glass with a great number of holes (vesicles) that remain after trapped gas has escaped from the solidifying melt.
- Pyroclast
- A volcanic rock fragment ejected into the air during an eruption.
- Rhyolite
- A light-brown to gray, fine-grained extrusive igneous rock with a felsic composition. The extrusive equivalent of granite.
- Sill
- A sheetlike concordant intrusion formed by the injection of magma between parallel layers of preexisting bedded rock.
- Stock
- An irregular mass of coarse-grained igneous rock less than 100 square kilometers in area.
- Tuff
- Any volcanic rock lithified from pyroclasts.
- Ultramafic rock
- An igneous rock consisting of mafic minerals and containing less than 10% feldspar.
- Vein
- A sheetlike deposit of minerals precipitated in fractures or joints that are foreign to the host rock.
- Viscosity
- A measure of a fluid's resistance to flow.
- Volcanic ash
- Extremely small fragments, usually of glass, that form when escaping gases force a fine spray of magma from a volcano.