Chapter 4: Igneous Rocks: Solids from Melts Flashcards
andesite
A volcanic rock type intermediate in composition between rhyolite and basalt.
basalt
A fine-grained, dark, mafic igneous rock composed largely of plagioclase feldspar and pyroxene.
batholith
A great irregular mass of coarse-grained igneous rock that covers at least 100 km2; the largest pluton.
concordant intrusion
An intrusive igneous rock whose boundaries lie parallel to 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.
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.
discordant intrusion
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 cooled magma that erupts 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 downward into the subduction zone.
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.
granite
A felsic, coarse-grained, intrusive igneous rock composed of quartz, orthoclase feldspar, sodium-rich plagioclase feldspar, and micas.
granodiorite
A light-colored, coarse-grained intrusive igneous rock similar to granite in having abundant quartz, but whose predominant feldspar is plagioclase, not orthoclase.
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 pyroxenes and olivines) rich in iron and magnesium and relatively 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.
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.
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
peridotite
A coarse-grained ultramafic intrusive igneous rock composed of olivine with small amounts of pyroxene and amphibole.
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.
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 km2 in area.
tuff
Any volcanic rock lithified from pyroclasts
ultramafic rock
An igneous rock consisting primarily of mafic minerals and containing less than 10 percent feldspar.
vein deposit (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.
