Geology Chapter 4 Vocab.

Front 1

intrusive igneous rock

Back 1

a rock that has forced its way into surrounding rock

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country rock

Back 2

rock surrounding intrusive igneous rocks.

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extrusive igneous rock

Back 3

rocks that form when lava or other material erupts from volcanoes. rapid cooling at earth's surface produces the finely grained texture or glassy appearance.

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pyroclasts

Back 4

volcanic rock fragment ejected into the air during an eruption.

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volcanic ash

Back 5

extremely small fragments, usually of glass, that form when escaping gases force a fine spray of magma from a volcano.

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tuff

Back 6

any volcanic rock lithified from pyroclasts.

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pumice

Back 7

frothy mass of volcanic glass with a great number of vesicles.

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obsidian

Back 8

glassy volcanic rock that contains only tiny vesicles and so is solid and dense.

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porphyry

Back 9

an igneous rock that has a mixed texture in which large crystals "float" in a predominantly fine crystalline matrix.

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granite

Back 10

a felsic, coarse-grained, intrusive igneous rock composed of quartz, orthoclase feldspar, sodium-rich plagioclase feldspar, and micas. Intrusive equivalent of rhyolite.

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rhyolite

Back 11

extrusive equivalent of granite. more finely grained than granite, though.

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intermediate igneous rocks

Back 12

midway between felsic and mafic. neither rich in silica nor poor in it.

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granodiorite

Back 13

light-colored felsic rock that looks something like granite.

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diorite

Back 14

contains less silica and is dominated by plagioclase feldspar, with little or no quartz.

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dacite

Back 15

volcanic equivalent of granodiorite

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andesite

Back 16

volcanic equivalent of diorite. derive name from andes mountains

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gabbro

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coarsely grained, dark grey intrusive igneous rock with even less silica than is found in intermediate igneous rocks.

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basalt

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dark gray to black and is the fine grained extrusive equivalent of gabbro. most abundant igneous rock of the crust, underlies virtually the entire seafloor.

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periodite

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dark greenish gray rock made up primarily of olivine with smaller amounts of pyroxene.

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viscosity

Back 20

the measure of a liquid's resistance to flow

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partial melting

Back 21

incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures.

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decompression melting

Back 22

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 heat.

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magma chambers

Back 23

magma-filled cavities in the lithosphere that form as rising drops of melted rock push aside surrounding solid rock.

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magmatic differentiation

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a process by which rocks of varying composition can arise from a uniform parent magma

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fractional crystallization

Back 25

process by which the crystals formed in a cooling magma are segregated from the remaining liquid.

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plutons

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large igneous bodies formed at depth in earth's crust.

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batholith

Back 27

largest plutons, are great irregular masses of coarse-grained igneous rock that by definition cover at lease 100 square kilometers.

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stocks

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an irregular mass of coarse-grained igneous rock less than 100 square km in area.

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discordant intrusions

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cut across the layers of the country rock that they intrude

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sill

Back 30

sheetlike body formed by the injection of magma between parallel layers of preexisting bedding rock

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concordant intrusion

Back 31

boundaries lie parallel to layers, whether or not the layers are horizontal.

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dikes

Back 32

major route of magma transport in the crust. cut across layers of bedding in country rock and so are discordant

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veins

Back 33

deposits of minerals found within a rock fracture that are foreign to the host rock.

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pegmatites

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veins of extremely coarse-grained granite cutting across a much finer grained country rock.

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hydrothermal veins

Back 35

vein filled with minerals that contain large amounts of chemically bound water and are known to crystallize from hot-water solutions.

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ophiolite suites

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consist of deep-sea sediments, submarine basaltic lavas, and mafic igneous intrusions.

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mafic rock

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a dark colored igneous rock containing minerals such as pyroxenes and olivines rich in iron and magnesium and relatively poor in silica.

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felsic rock

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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.

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ultramafic rock

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igneous rock consisting primarily of mafic minerals and containing less than 10 percent feldspar.