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chp 5
terms
34
Geology
Undergraduate 1
10/16/2007

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Term
Magma
Definition
Molten rock that has not reached earths surface
Term
Intrusive
Definition
igneous rocks formed by subsurface cooling of magma. Coarse grain because slow rates of cooling
Term
Lava
Definition
extruded molten rock
Term
Extrusive
Definition
igneous rocks formed from molten rock. Fast cooling fined grain
Term
Partial melting
Definition
process of rock melting in which minerals with low melting points melt before minerals with higher melting points as a rock mass is heated and/or subjected to a decrease in pressure
Term
Magmatic fractionation
Definition
concentration of crystals of particular mineral in portions of magma as it cools
Term
Crystal settling
Definition
first crystals to form in a cooling magma settle to the bottom of magma chamber
Term
Filter pressing
Definition
"mush" of precipitated crystals is separated from the magma by earths movements
Term
Phaneritic
Definition
textural term; individual mineral crystals can be seen from unaided eye
Term
Aphanitic
Definition
textural term; individual mineral crystals to small to see
Term
Glassy
Definition
textural term; rapid cooling of lava gives glassy appearance
Term
Porphyritic
Definition
large crystals enclosed by finer-grained matrix. Interrupted cooling history
Term
Porphry
Definition
large crystals enclosed by finer-grained matrix. Interrupted cooling history
Term
Phenocrysts
Definition
large crystals enclosed by finer-grained matrix. Interrupted cooling history
Term
Groundmass
Definition
fine grain
Term
Pyroclastic
Definition
rock material ejected during volcanic eruption
Term
Mafic
Definition
rock or minerals high in magnesium and iron and the magmas from which they form
Term
Felsic
Definition
igneous rocks with high percentage of light colored minerals(quartz, feldspar, feldspathoids, muscorite)
Term
Ultramafic
Definition
igneous rocks composed mostly of mafic minerals or magma from which they are formed
Term
Dunite
Definition
ultramafic igneous rock, mostly olivine
Term
Obsidian
Definition
Dark colored, amorphous material, forms by superfast cooling
Term
Tachylyte
Definition
Volcanic glass of various colors found in chilled margins of intrusive igneous bodies formed from basaltic magma
Term
Granite
Definition
coarse grain igneous rock, major component of continental crust
Term
Granodiorite
Definition
less potassium feldspar than granite
Term
Andesite
Definition
fined grain igneous rock; extrusive; found in andes mountains; 25-40% amphibole, pyroxime and biotite
Term
Basalt
Definition
dark colored, fined grained, extrusive igneous rock; calcic plagioclase and pyroxenes
Term
Peridotite
Definition
coarse grain, ultramafic, plutonic, igenouse rock, composed mostly of olivine. Major component of upper mantle
Term
Komatiite
Definition
suite of rare igneous rocks noted by presence of ultramafic lavas
Term
Tabular
Definition
descriptive term; body is bigger than other part
Term
Discordant
Definition
intrusive igneous body that cuts across bedding, foliation or structure of county rock into which rock intrudes
Term
Dike
Definition
tabular, discordant, intrusive, igneous body
Term
Concordant
Definition
igneous intrusion whose surfaces are parallel to layering of the intruded rock
Term
Sill
Definition
tabular, concordant, intrusive igneous body
Term
Massive
Definition
largest dimension is less than 10 times smallest dimension
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