Chapter 06 Igneous Rocks

As compared to aphanitic igneous rocks, phaneritic rocks are ____________. a. coarser grained b. finer grained c. more mafic d. more felsic

a. coarser grained

As compared to coarse-grained igneous rocks, all fine-grained igneous rocks ____________. a. cool and solidify more quickly b. cool and solidify more slowly c. solidify at higher temperatures d. solidify at lower temperatures

a. cool and solidify more quickly

Which type of magma has the greatest silica content? a. felsic b. intermediate c. mafic d. ultramafic

a. felsic

Large igneous provinces are formed by ___________, which can flow tens to hundreds of kilometers. a. flood basalts b. sills c. super plumes d. None of the above are correct.

a. flood basalts

If a body of magma becomes more felsic, its viscosity will ____________. a. increase b. decrease c. stay the same

a. increase

When magma crystallizes, ____________ are formed. a. intrusive igneous rocks b. extrusive igneous rocks c. volatiles d. pyroclastic debris

a. intrusive igneous rocks

Magma tends to _____________. a. move upward, away from where it formed b. move downward, away from where it formed c. move laterally d. stay in one place

a. move upward, away from where it formed

In Bowen's discontinuous reaction series, the first mineral to crystallize from a mafic melt is ____________. a. olivine b. plagioclase c. pyroxene d. quartz

a. olivine

Stoping by magmas occurs when ____________. a. pieces of surrounding country rock are broken off and assimilated b. the magma stops flowing and starts to solidify c. the magma becomes fully solidified to form intrusive rock d. the magma alters a thin rind of surrounding country rock

a. pieces of surrounding country rock are broken off and assimilated

An igneous rock with a mixed texture of coarse grains (phenocrysts) surrounded by fine crystals (groundmass) is termed ____________. a. porphyritic b. phaneritic c. aphanitic d. necrotic

a. porphyritic

A sill is a (an)____________. a. sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock b. cooled layer of lava c. intrusion formed within the magma chamber of a volcano d. sheet-like intrusion that cuts across preexisting layers

a. sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock

An island volcanic arc occurs at ____________. a. the Aleutian Islands of Alaska b. the Andes Mountains c. Hawaii d. Mt. St. Helens, Washington

a. the Aleutian Islands of Alaska

Very early in Earth's history, it was so hot that the surface was likely entirely molten. a. true b. false

a. true

Most commonly, felsic igneous rocks ____________. a. contain more iron and magnesium than intermediate rocks b. are lighter in color than mafic rocks c. are darker in color than mafic rocks d. are found in oceanic crust

b. are lighter in color than mafic rocks

If the volatile content of magma is increased, its viscosity will ____________. a. increase b. decrease c. stay the same

b. decrease

Pillow basalts, shown below, attain their distinctive blob-like shapes because their parent lavas do not travel far prior to solidification. This is because the parent lavas ____________. a. are completely devoid of volatiles and thus travel slowly b. erupt underwater and thus cool very quickly c. are highly felsic and thus travel slowly d. are ultramafic and thus freeze at exceptionally high temperatures

b. erupt underwater and thus cool very quickly

All of the Earth's internal heat was acquired very early in its history through meteoric impact and differentiation of the core. The Earth's interior loses heat to space but does not currently receive heat through any known process. a. true b. false

b. false

Vesicles are a term used to describe a texture in __________ igneous rocks. a. crystalline b. glassy c. pyroclastic

b. glassy

A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock. These newly formed magmas are ____________. a. ultramafic b. mafic c. felsic d. intermediate

b. mafic

Volcanoes that do NOT occur along either present or emergent plate boundaries are associated with ____________. a. continental rifts b. mantle hot spots c. mid-ocean ridges d. subduction zones

b. mantle hot spots

When rock is partially melted, the chemistry of the melt is ____________. a. more mafic than the original chemistry of the rock that was partially melted b. more felsic than the original chemistry of the rock that was partially melted c. identical to the original chemistry of the rock that was partially melted d. completely unpredictable (it could be more mafic or more felsic)

b. more felsic than the original chemistry of the rock that was partially melted

If a body of magma is subjected to fractional crystallization, the rock that results is expected to be ____________. a. identical in chemical composition to the magma b. more mafic than the magma c. more felsic than the magma

b. more mafic than the magma

Bowen's continuous reaction series describes the crystallization behavior of a single mineral (with variable chemical composition), ____________. a. olivine b. plagioclase c. pyroxene d. quartz

b. plagioclase

The silicate mineral that is found in the greatest variety of igneous rocks is ____________. a. olivine b. plagioclase c. pyroxene d. quartz

b. plagioclase

A blob-like igneous rock body that has cooled beneath the surface of Earth is ____________. a. guyot b. pluton c. lava flow d. andesite

b. pluton

Pegmatites, which occur in dikes, are unusual among shallow intrusive rocks in that they ____________. a. possess porphyritic texture b. possess exceptionally coarse grains c. are mineralogically identical to the extrusive rock basalt d. are glassy, cooling so rapidly that crystals do not have time to form

b. possess exceptionally coarse grains

The geotherm is the rate of change of ____________. a. pressure with depth in Earth's interior b. temperature with depth in Earth's interior c. temperature with altitude in Earth's atmosphere d. temperature with latitude on Earth's surface

b. temperature with depth in Earth's interior

A continental volcanic arc occurs at ____________. a. the Aleutian Islands of Alaska b. the Andes Mountains c. Hawaii d. Japan

b. the Andes Mountains

A famous example of hot-spot volcanism occurs at ____________. a. the Aleutian Islands of Alaska b. the Andes Mountains c. Hawaii d. Mt. St. Helens, Washington

c. Hawaii

Radioactive isotopes, differentiation of Earth's iron core, gravity-driven compression, and meteoric bombardment all caused early Earth to ____________. a. glow brighter than the Sun b. be much cooler than at present c. be much hotter than at present d. be much more oblong than at present

c. be much hotter than at present

All other factors being equal, intrusive rocks that form deep within Earth ____________ than intrusive rocks that cool near the surface. a. are more felsic b. contain a smaller proportion of volatiles c. cool more slowly d. cool more rapidly

c. cool more slowly

If you found tuff deposits at an ___________ igneous setting, you could conclude that the lava had a ___________ viscosity content. a. intrusive; high b. intrusive; low c. extrusive; high d. extrusive; low

c. extrusive; high

Volatiles refer to substances that ____________. a. crystallize most rapidly out of a melt b. melt immediately upon contact with a hot body of magma c. have a tendency to evaporate and are stable as gases

c. have a tendency to evaporate and are stable as gases

A volcanic neck, such as that seen at Shiprock, New Mexico (below), is a (an) ____________. a. sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock b. cooled layer of lava c. intrusion formed within the magma chamber of a volcano d. sheet-like intrusion that cuts across preexisting layers

c. intrusion formed within the magma chamber of a volcano

The difference between lava and magma is that magma ____________. a. is light in color, whereas lava is dark b. usually has mafic composition, whereas lava usually has felsic composition c. is found beneath the Earth's surface, whereas lava has reached the surface d. flows more quickly than lava

c. is found beneath the Earth's surface, whereas lava has reached the surface

Geologically, melts are equivalent to both ____________ and ____________. a. felsic magma; mafic magma b. felsic lava; mafic lava c. lavas; magmas d. fine-grained igneous rocks; coarse-grained igneous rocks

c. lavas; magmas

The difference between magma and lava is ____________. a. magma cools more rapidly than lava b. magma is found at the surface, whereas lava is found below the surface c. magma is found beneath the surface, whereas lava is found at the surface d. There is no difference; the two terms mean the same thing.

c. magma is found beneath the surface, whereas lava is found at the surface

Injecting hot fudge into ice cream is an appropriate analogy for which cause of magma melt? a. Melting due to a decrease in pressure b. melting due to an addition of volatiles c. melting due to heat transfer from rising magma d. All of the above are correct.

c. melting due to heat transfer from rising magma

If a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be ____________. a. identical in chemical composition to the source rock b. more mafic than the source rock c. more felsic than the source rock

c. more felsic than the source rock

Mt. Kilimanjaro and the Basin and Range Province are the result of _____________. a. converging plates b. subducting plates c. rifting d. None of the above are correct.

c. rifting

A volcano emits ash, which falls from the sky, settles in layers, and is eventually cemented. The resulting rock is termed ____________. a. pumice b. granite c. tuff d. ignimbrite

c. tuff

Important volatiles in magmas include ____________. a. iron- and magnesium-rich minerals, such as olivine b. potassium and aluminum c. water and carbon dioxide d. trinitrotoluene and nitroglycerin

c. water and carbon dioxide

Ash and lava fragments that cascade down the sides of a volcano eventually settle and lithify to form ____________. a. basalt b. andesite c. welded tuff d. ash-fall tuff

c. welded tuff

Igneous rocks ____________. a. are formed through the freezing of melt b. can be produced at the surface of the Earth as well as deep below the surface c. are the most common type of rocks within Earth d. All of the above are correct.

d. All of the above are correct.

Large igneous provinces can cause ______________. a. sea level rise b. climate change c. extinction d. All of the above are correct.

d. All of the above are correct.

Viscosity depends on ____________. a. temperature b. volatile content c. silica content d. All of the above are correct.

d. All of the above are correct.

Which of the following is NOT a factor controlling the cooling rate of magma? a. depth of intrusion b. shape and size of magma body c. presence of circulating groundwater d. All of the above are factors.

d. All of the above are factors.

Bombs, ash, and cinders are all examples of ____________. a. intrusive igneous rocks b. hot spots c. volatiles d. pyroclastic debris

d. pyroclastic debris

Coarse-grained granite is most similar in mineral composition to fine-grained ____________. a. andesite b. basalt c. komatiite d. rhyolite

d. rhyolite

A dike is a (an) ____________. a. sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock b. cooled layer of lava c. intrusion formed within the magma chamber of a volcano d. sheet-like intrusion that cuts across preexisting layers

d. sheet-like intrusion that cuts across preexisting layers

In regard to the cooling of molten rock, a __________ volume and a __________ shape cools faster. a. larger; spherical b. larger; pancake c. smaller; spherical d. smaller; pancake

d. smaller; pancake

As compared to mafic igneous rocks, all felsic igneous rocks ____________. a. cool and solidify more quickly b. cool and solidify more slowly c. solidify at higher temperatures d. solidify at lower temperatures

d. solidify at lower temperatures