Deck 4: Igneous Rocks: Solids From Melts

Question 1

Which of the following best describes an andesite?

A)a coarse-grained,intermediate igneous rock
B)a fine-grained,intermediate igneous rock
C)a coarse-grained,felsic igneous rock
D)a fine-grained,felsic igneous rock

Answer 1

B

Question 2

Which of the following pairs of intrusive and extrusive rocks have the same chemical composition?

A)diorite and rhyolite
B)gabbro and rhyolite
C)gabbro and basalt
D)granite and andesite

Answer 2

C

Question 3

Which of the following best describes a rock with 10-millimeter-long plagioclase crystals set in a fine-grained matrix of 0.5-millimeter-long crystals?

A)obsidian
B)pluton
C)porphyry
D)tuff

Answer 3

C

Question 4

What geologist is credited with figuring out the origin of granite?

A)N)L.Bowen
B)Charles Darwin
C)James Hutton
D)Alfred Wegener

Question 5

What is the approximate silica content of granite?

A)30%
B)50%
C)70%
D)90%

Question 6

Which of the following igneous rocks has the lowest silica content?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 7

Which of the following properties does not depend on the chemical composition of an igneous rock/magma?

A)grain size
B)melting temperature
C)mineralogy
D)viscosity

Question 8

Which of the following statements is true?

A)Gabbro has a higher melting temperature than granite.
B)Gabbro has a higher potassium content than granite.
C)Gabbro has a higher silica content than granite.
D)Gabbro has a higher viscosity than granite.

Question 9

Which of the following minerals is rarely found in felsic igneous rocks?

A)olivine
B)orthoclase feldspar
C)plagioclase feldspar
D)quartz

Question 10

Which of the following rocks is a volcanic rock made up of lithified pyroclastic material?

A)basalt
B)granodiorite
C)obsidian
D)tuff

Question 11

Which of the following igneous rocks crystallizes at Earth's surface?

A)basalt
B)gabbro
C)granite
D)peridotite

Question 12

What type of volcanic rock contains a large number of vesicles (bubbles)that form when gases escape from the solidifying melt?

A)granite
B)obsidian
C)porphyry
D)pumice

Question 13

Which of the following best describes a rhyolite?

A)fine-grained igneous rock rich in silica
B)fine-grained igneous rock poor in silica
C)coarse-grained igneous rock rich in silica
D)coarse-grained igneous rock poor in silica

Question 14

Andesite is an example of a(n)__________ igneous rock.

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 15

Which of the following igneous rocks does not consist of volcanic glass?

A)ash
B)gabbro
C)obsidian
D)pumice

Question 16

Which of the following types of igneous rocks are rarely found as lavas?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 17

Felsic igneous rocks contain abundant __________ silicate minerals.

A)double-chain
B)framework
C)isolated tetrahedra
D)single-chain

Question 18

Which of the following minerals is common in both felsic and mafic igneous rocks?

A)olivine
B)plagioclase feldspar
C)pyroxene
D)quartz

Question 19

Which of the following igneous rocks has the same chemical composition as basalt?

A)andesite
B)diorite
C)gabbro
D)rhyolite

Question 20

Where would you expect to find the largest crystals in a lava flow?

A)near the top surface of the flow
B)near or just below the center of the flow
C)near the bottom surface of the flow
D)throughout the flow

Question 21

Which of the following processes would most likely yield a granitic magma?

A)partial melting of subducted oceanic crust and sediments
B)partial melting of the continental crust
C)partial melting of the core
D)partial melting of the upper mantle

Question 22

What type of magma forms at mid-ocean ridges?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 23

The famous Mother Lode of the 1849 California gold rush is an example of

A)a basaltic dike.
B)a hydrothermal vein.
C)a volcanic tuff.
D)a granitic pluton.

Question 24

Which of the following is not part of an ophiolite suite?

A)basaltic dikes
B)granitic plutons
C)deep-sea sediments
D)massive gabbros

Question 25

Compared with the mantle beneath a mid-ocean ridge,the mantle above a subduction zone

A)contains less water and melts at a lower temperature.
B)contains less water and melts at a higher temperature.
C)contains more water and melts at a lower temperature.
D)contains more water and melts at a higher temperature.

Question 26

At what temperature do minerals crystallize in hydrothermal veins?

A)approximately 300°C
B)approximately 600°C
C)approximately 900°C
D)approximately 1500°C

Question 27

Which of the following types of igneous rocks crystallizes deep within Earth's crust?

A)andesite
B)basalt
C)gabbro
D)rhyolite

Question 28

Which of the following minerals is most likely to settle to the bottom of a magma chamber?

A)olivine
B)plagioclase feldspar
C)pyroxene
D)quartz

Question 29

How can a sill be distinguished from a lava flow?

A)A sill is generally finer-grained than a lava flow.
B)Rocks above and below a sill will show evidence of heating,but only the rocks below a lava flow will show evidence of heating.
C)Sills generally have vesicles; lava flows generally do not have vesicles.
D)Sills generally overlie soils; lava flows do not generally overlie soils.

Question 30

Which of the following igneous bodies is a concordant intrusive rock?

A)dike
B)pluton
C)sill
D)stock

Question 31

For a rock of a specific composition,which of the following statements is true?

A)The amount of partial melt decreases with increasing temperature.
B)The melting temperature increases with increasing pressure.
C)The melting temperature increases with increasing water content.
D)All of the statements above are true.

Question 32

Which of the following lists is in the correct order of increasing silica content?

A)diorite,granite,gabbro
B)gabbro,diorite,granite
C)gabbro,granite,diorite
D)granite,diorite,gabbro

Question 33

In order to rise through the crust,magmas make space by all of the following processes,except

A)breaking off large blocks of rock that sink into the magma chamber.
B)following preexisting networks of caverns.
C)melting surrounding rocks.
D)wedging open the overlying rock.

Question 34

What type of rock makes up most of the Hawaiian Islands?

A)andesite
B)basalt
C)granite
D)peridotite

Question 35

Which of the following magma compositions will be produced by partial melting of the upper mantle?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 36

Large igneous bodies that form at depth in Earth's crust are called

A)dikes.
B)plutons.
C)sills.
D)veins.

Question 37

Which of the following minerals crystallizes from a magma at the lowest temperature?

A)calcium-rich feldspar
B)olivine
C)pyroxene
D)quartz

Question 38

Fluid-induced melting generates magmas in which of the following tectonic settings?

A)mantle plumes
B)subduction zones
C)mid-ocean ridges
D)transform faults

Question 39

Which of the following tectonic settings has the greatest range in magma compositions?

A)convergent plate boundaries
B)transform plate boundaries
C)divergent plate boundaries
D)hot spots (mantle plumes)

Question 40

Which of the following statements about felsic igneous rocks is true?

A)Felsic rocks contain less silica than mafic rocks.
B)Felsic rocks crystallize at lower temperatures than mafic rocks.
C)Felsic rocks tend to be darker colored than mafic rocks.
D)Felsic rocks tend to be finer grained than mafic rocks.

Question 41

Which of the following minerals does not normally occur in basalt?

A)olivine
B)pyroxene
C)plagioclase feldspar
D)quartz

Question 42

The process whereby two different magmas mix is called

A)rock mixing.
B)melt mixing.
C)magma mixing.
D)magma mingling.

Question 43

Bowen's Reaction Series describes

A)how fast crystals grow from cooling magmas.
B)how fast magmas cool.
C)how magmas react to cooling.
D)the sequence in which minerals form when magmas cool.

Question 44

When equal amounts of a basaltic and granitic magma mix,the resulting magma is

A)mafic.
B)basaltic.
C)felsic.
D)andesitic.

Question 45

Magmas fall into one of the following groups:

A)felsic,mafic or intermediate
B)mafic or intermediate
C)intermediate or felsic
D)extrusive or intrusive

Question 46

Magma is,by definition,

A)molten rock ejected into the air.
B)solid rock ejected into the air.
C)molten rock below the surface.
D)molten rock on the surface.

Question 47

Typically,__________ volume percent partial melting of upper-mantle peridotite occurs to generate basaltic magmas beneath mid-ocean ridges.

A)1 to 2
B)10 to 15
C)15 to 20
D)30 to 50

Question 48

The main difference between intrusive and extrusive igneous rocks is

A)silica composition.
B)where they solidify.
C)viscosity.
D)intrusive rocks are more felsic.

Question 49

Which of the following describes an ophiolite suite,beginning at the base?

A)peridotite,gabbro,sheeted dikes,pillow basalt,sediments
B)gabbro,peridotite,sheeted dikes,sediments,pillow basalt
C)pillow basalt,sheeted dikes,gabbro,peridotite,sediments
D)sediments,pillow basalt,gabbro,peridotite,sheeted dikes

Question 50

Which igneous rock is the most abundant component of the crust and makes up nearly all of the seafloor?

A)andesite
B)basalt
C)granite
D)peridotite

Question 51

Chunks of rocks that break off from country rocks and fall into magmas are called

A)wall rocks.
B)xenoliths.
C)country rocks.
D)foreign rocks.

Question 52

The classification of igneous rocks is dependent on texture and

A)the relative proportion of silicate minerals.
B)the relative proportion of pyroclastic material.
C)the relative proportion of phenocryst minerals.
D)the relative proportion of vesicles.

Question 53

If a magma undergoes fractional crystallization,the remaining magma will be

A)more felsic.
B)less viscous.
C)more mafic.
D)exactly the same.

Question 54

What is the origin of the word "felsic" in the context of igneous rock classification?

A)iron (Fe)and silica (SiO₂)
B)feldspar and silica
C)iron and magnesium (Mg)
D)It means "light" colored.

Question 55

The largest forms of igneous intrusions are called

A)plutons.
B)stocks.
C)sills.
D)batholiths.

Question 56

Which igneous rock was used by Native Americans to produce arrowheads?

A)granite
B)ophiolite
C)basalt
D)obsidian

Question 57

Magmatic stoping is the term used to describe how magmas

A)differentiate.
B)form.
C)move through the crust.
D)solidify.

Question 58

Mantle plumes generate large volumes of ________ magmas.

A)andesitic
B)peridotitic
C)rhyolitic
D)basaltic

Question 59

The rock surrounding an intrusive igneous body is referred to as the

A)encasing rock.
B)enclosing rock.
C)crustal rock.
D)country rock.

Question 60

How much partial melting of upper-mantle peridotite is needed to generate some basaltic melt?

A)1% to 2% volume
B)10% to 15% volume
C)20% to 30% volume
D)more than 50%

Question 61

What was the initial composition of the melt that the Palisades sill formed from?

A)mafic
B)intermediate
C)felsic
D)ultramafic

Question 62

When generating granite from basalt via crystal fractionation we would need approximately ____ of basalt for every km of granite produced.

A)½ cubic km
B)1 cubic km
C)5 cubic km
D)10 cubic km

Question 63

Geologists studying magmatic differentiation had difficulty explaining the unexpectedly large volume of

A)andesite.
B)gabbro.
C)diorite.
D)granite.

Question 64

Ultramafic lava flows were more common in the early history of the earth than now because

A)ultramafic melts were more common in the past.
B)Earth's crust was hotter in the past.
C)Earth's mantle was cooler in the past.
D)plate tectonics had not been initiated.

Question 65

Which of the following rock types are best mined for rare elements,such as lithium and beryllium?

A)dacites
B)gabbros
C)pegmatites
D)tuffs

Question 66

Crystal fractionation from basalt cannot by itself account for the global volume of __________ on earth.

A)andesites
B)gabbros
C)diorites
D)granites

Question 67

Approximately how much volcanic rocks forms annually at subduction zones?

A)0.1 km³
B)1 km³
C)20 km³
D)100 km³

Question 68

Approximately how much basalt forms annually at mid-ocean ridges?

A)0.1 km³
B)1 km³
C)20 km³
D)100 km³

Question 69

Ultramafic lava flows are relatively uncommon.Why is that?

A)They are rarely generated in the mantle.
B)They have a high melting point and the crustal temperature is too low.
C)They are high density and therefore do not rise in the mantle.
D)They have high viscosity like felsic melts.

Question 70

How do we know that the initial composition of the melt that the Palisades sill was mafic?

A)There is basalt in the contact zone where the melt chilled.
B)The sill material contains feldspar.
C)The sill material contains pyroxene.
D)The magma in sill underwent fractional crystallization.

Question 71

What is the correct sequence of rocks (bottom to top)of an ophiolite suite? 1 = deep-sea sediment,2 = gabbro,3 = peridotite,4 = pillow lava,5 = sheeted dike complex

A)1,2,3,4,5
B)1,3,5,2,4
C)1,4,5,2,3
D)5,4,3,2,1

Question 72

The presence of water will ________ the melting temperature of a rock.

A)increase
B)raise
C)decrease
D)not affect

Question 73

Which of the following types of igneous rocks are rarely found as lavas today?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 74

When a large mineral surrounded by much smaller minerals in an igneous rock,the mineral in question is called a

A)porphyry.
B)phenocryst.
C)pumice.
D)pyroclast.

Question 75

What type of magma forms when the upper mantle undergoes decompression melting?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 76

What is the overall composition of the Palisades sill located near New York?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 77

At approximately what temperature do olivine and calcium-rich plagioclase feldspar crystallize from a mafic melt?

A)300°C
B)600°C
C)1200°C
D)2000°C