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Glossary
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Below you will find key words and concepts that you should remember from this chapter.
andesite  Fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals.
(See page(s) 54)
basalt  A fine-grained, mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
(See page(s) 54)
batholith  A large discordant pluton with an outcropping area greater than 100 square kilometers.
(See page(s) 58)
Bowen’s reaction series  The sequence in which minerals crystallize from a cooling basaltic magma.
(See page(s) 63)
chill zone  In an intrusion, the finer-grained rock adjacent to a contact with country rock.
(See page(s) 51)
coarse-grained rock  Rock in which most of the grains are larger than 1 millimeter (igneous) or 2 millimeters (sedimentary).
(See page(s) 52)
contact  Boundary surface between two different rock types or ages of rocks.
(See page(s) 51)
country rock  Any rock that was older than and intruded by an igneous body.
(See page(s) 51)
crystal settling  The process whereby the minerals that crystallize at a high temperature in a cooling magma move downward in the magma chamber because they are denser than the magma.
(See page(s) 64)
diapir  Bodies of rock (e.g., rock salt) or magma that ascend within Earth’s interior because they are less dense than the surrounding rock.
(See page(s) 59)
differentiation  Separation of different ingredients from an originally homogeneous mixture.
(See page(s) 64)
dike  A tabular, discordant intrusive structure.
(See page(s) 58)
diorite  Coarse-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar and the rest is ferromagnesian minerals.
(See page(s) 54)
extrusive rock  Any igneous rock that forms at Earth’s surface, whether it solidifies directly from a lava flow or is pyroclastic.
(See page(s) 51)
fine-grained rock  A rock in which most of the mineral grains are less than one millimeter across (igneous) or less than 1/16 mm (sedimentary).
(See page(s) 52)
gabbro  A mafic, coarse-grained igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
(See page(s) 52)
geothermal gradient  Rate of temperature increase associated with increasing depth beneath the surface of Earth (normally about 25°C/km).
(See page(s) 61)
granite  A felsic, coarse-grained, intrusive igneous rock containing quartz and composed mostly of potassium- and sodium-rich feldspars.
(See page(s) 51)
igneous rock  A rock formed or apparently formed from solidification of magma.
(See page(s) 51)
intermediate  Rock with a chemical content between felsic and mafic compositions.
(See page(s) 57)
intrusion (intrusive structure)  A body of intrusive rock classified on the basis of size, shape, and relationship to surrounding rocks.
(See page(s) 57)
intrusive rock  Rock that appears to have crystallized from magma emplaced in surrounding rock.
(See page(s) 51)
lava  Magma on Earth’s surface.
(See page(s) 51)
mafic  Silica-deficient igneous rock with a relatively high content of magnesium, iron, and calcium.
(See page(s) 54)
magma  Molten rock, usually mostly silica. The liquid may contain dissolved gases as well as some solid minerals.
(See page(s) 51)
mantle plume  Narrow column of hot mantle rock that rises and spreads radially outward.
(See page(s) 61)
peridotite  An ultramafic rock composed primarily of the mineral olivine.
(See page(s) 57)
pluton  An igneous body that crystallized deep underground.
(See page(s) 58)
plutonic rock  Igneous rock formed at great depth.
(See page(s) 52)
rhyolite  A fine-grained, felsic, igneous rock made up mostly of feldspar and quartz.
(See page(s) 54)
rock  Naturally formed, consolidated material composed of grains of one or more minerals. (There are a few exceptions to this definition.
(See page(s) 50)
rock cycle  A theoretical concept relating tectonism, erosion, and various rock-forming processes to the common rock types.
(See page(s) 50)
silicic (felsic)  Silica-rich igneous rock or magma with a relatively high content of potassium and sodium.
(See page(s) 54)
sill  A tabular intrusive structure concordant with the country rock.
(See page(s) 58)
stock  A small discordant pluton with an outcropping area of less than 100 square kilometers.
(See page(s) 58)
texture  For igneous rocks, refers to the size of mineral crystals in the rock.
(See page(s) 52)
ultramafic rock  Rock composed entirely or almost entirely of ferromagnesian minerals.
(See page(s) 57)
volcanic neck  An intrusive structure that apparently represents magma that solidified within the throat of a volcano.
(See page(s) 57)
xenolith  Fragment of rock distinct from the igneous rock in which it is enclosed.
(See page(s) 51)







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