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100 Cards in this Set

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What is the most important factor affecting the texture of an igneous rock?
The rate of cooling of magma
A mass of solid, felsic glass; sharp-edged pieces split off its surface when it is hit w/ a hammer:
Obsidian (volcanic glass)
Igneous rock texture with crystals that are too small to be seen w/ the naked eye:
Aphanitic (extrusive)
What type of structure is Mount Rushmore?
A famous granite batholith
What extrusive (fine-grained) igneous rock contains primarily quartz, potassium feldspar, and muscovite?
Rhyolite
What mineral crystallizes at the lowest temperature during Bowen’s reaction series?
Quartz
Igneous rock composition that contains a small amount of silica:
Mafic
Describe groundmass:
Small crystals (light color)
Which igneous rock texture has 2 or more distinctly different-sizes of mineral grains?
Porphyritic
What igneous rock texture is formed when magma cools so quickly that crystals do not have time to form?
Glassy; also called “volcanic glass” (extrusive)
Which igneous rock texture has crystals that are large enough to be seen w/ the naked eye?
Phaneritic (intrusive)
Rock that forms from the cooling or crystallization of magma:
Igneous rock
What extrusive (fine-grained) igneous rock contains primarily plagioclase feldspar, amphibole, quartz and pyroxene?
Andesite
Igneous rock texture that forms from the initial slow cooling then rapid cooling of magma:
Porphyritic
Explain the continuous reaction of Bowen’s reaction series:
1) Plagioclase feldspars that are RICH IN CALCIUM and low in sodium will be the first minerals to crystallize at a HIGH TEMPERATURE.

2) As you move to down to the bottom of the chart the newly formed plagioclase feldspars will be RICH IN SODIUM and low in calcium; the last minerals will crystallize at a LOW TEMPERATURE.
What mineral crystallizes at the highest temperature during Bowen’s reaction series?
Olivine
The sequence or order in which minerals crystallize from magma:
Fractional Crystallization
Igneous rock texture that forms when magma cools and crystallizes above the Earth’s surface:
Extrusive
Igneous rock texture that contain(s) small holes which are formed by the expansion of bubbles of gas or steam during the solidification of the rock:
Vesicular texture
Magma/rock composition that has a moderate amount of silica:
Intermediate
What igneous rock contains the greatest amount of quartz?
Granite
Describe phenocrysts:
Large crystals (dark color)
What rock feature is useful only in identifying igneous rocks?
Color (mafic, felsic, intermediate)
What igneous rock has the same texture as granite, but is mafic in composition?
Gabbro
The classification of igneous rocks is based on what 2 things?
Texture and mineral composition
What branch of Bowen's reaction series cools with a continuous change in composition?
Plagioclase feldspars
A glassy felsic volcanic rock that contains many vesicles; formed by the quick cooling of frothy lava:
Pumice
Peridotite has a(n) ____ composition and is made almost entirely from ____.
Ultramafic, olivine
The different compositional classes of igneous rocks are based on what?
Silica content
Describe the crystals formed in intrusive and extrusive rocks:
Intrusive-crystals are LARGE b/c they cool slowly

Extrusive-crystals are SMALL b/c they cool at a fast pace
Felsic composition w/ aphanitic texture:
rhyolite
Intermediate composition w/ aphanitic texture:
andesite
Mafic composition w/ aphanitic texture:
basalt
Extrusive felsic composition w/ porphyritic texture:
rhyolite porphyry
Extrusive intermediate composition w/ porphyritic texture:
andesite porphyry
Extrusive mafic composition w/ porphyritic texture:
basalt porphyry
Felsic composition w/ phaneritic texture:
granite
Intermediate composition w/ phaneritic texture:
diorite
Mafic composition w/ phaneritic texture:
gabbro
Ultramafic composition w/ phaneritic texture:
peridotite
Intrusive felsic composition w/ porphyritic texture:
granite porphyry
Intrusive intermediate composition w/ porphyritic texture:
diorite porphyry
Intrusive mafic composition w/ porphyritic texture:
gabbro porphyry
Felsic/intermediate composition w/ glassy texture:
obsidian
Felsic/intermediate composition w/ vesicular texture:
pumice
Mafic composition w/ vesicular texture:
scoria basalt
Pyroclastic texture that can have any composition:
welded tuff, volcanic breccia
Extrusive igneous rock cools ____, and intrusive rock cools ____.
Quickly, slowly
Magma/rock composition that has a large amount of silica:
Felsic (silicic)
How is extrusive rock most likely formed?
During volcanic eruptions
Name 2 famous batholiths:
1) Mount Rushmore (granite)
2) Stone Mountain (Georgia)
According to Bowen’s reaction series, which is the proper sequence of minerals crystallizing during the discontinuous reaction series?
Olivine – pyroxene – amphibole – biotite
What feature of an igneous rock involves the mineral content, and/or refers to the magma from which it solidified?
Composition
Pyroclastic rock formed by the welding together of hot shards of volcanic ash:
Welded Tuff
Igneous rock texture that forms when magma cools and crystallizes below the Earth’s surface:
Intrusive
What intrusive (coarse-grained) igneous rock contains primarily plagioclase feldspar, amphibole, quartz and pyroxene?
Diorite
According to Bowen's reaction series, what mineral has the highest crystallization temperature?
Olivine
Which rock type is most likely to contain calcium-rich feldspar?
Basalt
Completely or partially molten material, which on cooling solidifies to form an igneous rock:
Magma
What famous batholith exists in Texas?
Enchanted Rock
The large crystals in a porphyritic rock:
Phenocrysts
What does crystal size imply in igneous rocks?
Time allowed for cooling of the magma/lava
What is the composition of the earth's mantle?
Ultramafic
What igneous rock is ultramafic in composition?
Peridotite
Igneous rock texture that is formed when volcanic ash falls to the surface and causes fragments to stick together in large chunks:
Pyroclastic
What is the last mineral to crystallize from a melt in the Bowen's reaction series?
Quartz
Igneous rock composition that is dark in color:
Mafic
Extrusive igneous rocks are considered _________, whereas intrusive igneous rocks are considered _________.
“Volcanic” rocks b/c they form from lava extruded at the surface; “plutonic” rocks b/c they form from magma beneath the surface.
Dark colored “lava rock” w/ abundant vesicles:
Scoria basalt
What feature of an igneous rock involves the size of crystals and mineral grains?
Texture
What intrusive (coarse-grained) igneous rock contains primarily olivine and small amounts of pyroxene?
Peridotite
Igneous rock texture that forms from an initial slow cooling of magma followed by fast cooling:
Porphyritic texture
Intrusion that is made up of many plutons; immense masses of igneous rock:
Batholith
Igneous rock that forms when lava cools so fast that minerals cannot crystallize:
Obsidian, or volcanic glass
Igneous rock composition that is light in color:
Felsic (pinks, whites, etc.)
What extrusive (fine-grained) igneous rock contains primarily olivine, pyroxene, and calcium-rich plagioclase?
Basalt
Why do extrusive igneous rocks have smaller crystals than intrusive igneous rocks?
B/c intrusive igneous rocks cool slower than extrusive rocks.
Vertical intrusions that are formed when magma cuts across layers of rock:
Dikes (tabular intrusions)
An igneous rock that is coarse-grained and contains abundant quartz:
Granite
Igneous means:
"Fire"
What igneous rock texture forms both large and smalls crystals b/c it has 2 different cooling stages?
Porphyritic
The sequence of fractional crystallization in igneous rocks:
Bowen’s Reaction Series
Igneous rock that consists of large fragments of volcanic debris, either that fall through the air and accumulate, or that form when a lava flow breaks into pieces:
Volcanic breccia
Igneous rock that makes up most of the Earth’s mantle:
Peridotite
Igneous rock composition that contains the smallest amount of silica:
Ultramafic
Which type of intrusion is most likely to develop columnar jointing?
Sill
What is the first mineral to crystallize in the Bowen’s reaction series?
Olivine
Which type of intrusion generally contains granite?
Batholith (Pluton)
Describe the 2 stages of the formation of porphyritic rocks:
1) Magma cools slowly below the Earth’s surface - creates phenocrysts (large crystals)

2) Magma takes phenocrysts w/ it and erupts above Earth’s surface - the fast cooling creates even larger phenocrysts & newly formed groundmass (small crystals)
Horizontal intrusions that are formed when magma runs parallel to the rock layers:
Sills (Tabular intrusions)
What intrusive (coarse-grained) igneous rock contains primarily olivine, pyroxene, and calcium-rich plagioclase?
Gabbro
What are the 2 pyroclastic igneous rocks?
1) Tuff (welded)
2) Volcanic breccia
As a result of fractional crystallization and assimilation of surrounding rocks, the chemistry of a magma that slowly rises through continental crust will tend to become more ____ over time.
Felsic
What are the 3 glassy (non-fragmental) igneous rocks?
1) Obsidian
2) Scoria basalt
3) Pumice
Igneous rock composition that contains both dark and light crystals and grains:
Intermediate (“salt and pepper”)
What famous dike is actually believed to be a volcanic plug?
“Shiprock” (Mexico)
How do we classify intrusions?
According to size
What allows geologists to predict what minerals will be found together in igneous rocks?
Bowen's reaction series
What intrusive (coarse-grained) igneous rock contains primarily quartz, potassium feldspar, and muscovite?
Granite
Where is one of the few places in the world that you can see peridotite?
Tablelands-you can see slivers of the Earth’s uppermost mantle