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