Deck 3: Igneous Rocks

Question 1

Plutonic rocks are emplaced at depth yet they can be seen at the Earth's surface due mainly to ________.

A)catastrophic violent upheavals that bring them to the surface
B)continual ongoing intrusion after the magma solidifies
C)erosion of overlying rocks due to uplift
D)widespread igneous inversion

Answer 1

C

Question 2

Silicate igneous rocks make up the ________.

A)bulk of volcanic mountains but not much else on Earth
B)bulk of the Earth's crust and mantle
C)densest rocks and are mainly found in the core
D)majority of shallow rocks covering the continents but everything deeper is sedimentary and metamorphic

Answer 2

B

Question 3

The molten portion of magmas and lavas is made up of ________.

A)complex anion frameworks of oxygen with silicon and aluminum and cation modifiers made up of different amounts of calcium, sodium, iron, magnesium, and potassium
B)metamorphic fluids
C)silicate minerals that have already crystallized
D)solid high pressure forms of water, carbon dioxide, and sulfur dioxide

Answer 3

A

Question 4

The earliest formed crystals (phenocrysts)in a magma tend to be ________.

A)crowded and irregular in shape
B)small and clouded with inclusions of everything that formed later on
C)those that can form only at the lowest temperatures
D)larger and well formed because they have space to grow and a ready supply of ions

Question 5

All of the following are factors that affect the generation of magma except for ________.

A)heat
B)pressure
C)crystal size
D)volatiles

Question 6

Three processes contribute to the formation of every igneous rock: ________.

A)assimilation, crystallization, and dyke injection
B)extrusion, intrusion, and consolidation
C)partial melting, buoyant rise, and crystallization
D)volcanism, plutonism, and magmatic differentiation

Question 7

Which of the following is the major dissolved volatile constituent in both magmas and volcanic gases?

A)carbon monoxide
B)methane
C)nitrous oxide
D)water

Question 8

________ are dissolved in melts at depth but they have a tendency to evolve and vaporize at lower (atmospheric)pressure and drive volcanic processes.

A)Crystals of quartz and feldspar
B)Silica, sodium, and potassium
C)Volatiles
D)Volcanic lavas

Question 9

The process of ________ is driven by ________ and transforms a magma into an igneous rock.

A)crystallization, cooling (heat loss)
B)intrusion, overlying rock weight
C)partial melting, pressure increase
D)volcanism, internal heating

Question 10

The mechanism of magmatic differentiation involving the removal of denser, early formed high temperature mineral phases is ________.

A)assimilation
B)crystal settling
C)magma mixing
D)zone refining

Question 11

Explosive volcanic eruptions occur ________.

A)when crystallization forces exceed the strength of the volcano
B)in response to deflation of the volcano
C)when violently escaping gases evolve suddenly to drop the magma density and propel molten magma from the chamber
D)whenever basaltic magma extrudes on the seafloor

Question 12

The temperature within the Earth ________ with depth because rocks are poor conductors of heat and they contain small amounts of radioactive elements that generate heat.This gradual change in temperature with depth is called the ________.

A)increases, conductivity barrier
B)decreases, crustal thermocline
C)increases, geothermal gradient
D)increases, melting profile

Question 13

Which statement best describes the crystallization of magmas?

A)Early formed crystals are big and irregular in shape, but gradually get smaller and have better developed faces with time as they react with the residual melt.
B)A felsic magma produces only one rock type equal to the melt composition by crystallizing quartz, feldspar, and ferromagnesian minerals in fixed proportions and compositions until all of the melt is used up.
C)During crystallization, which can occur over an interval of about 200° C, the composition of the residual melt continuously changes as particular ions are selectively removed and incorporated into certain minerals that crystallize early at high temperature.
D)Like the freezing of water, cooling magmas hit their crystallization temperature and stop cooling until all the melt has crystallized, whereupon cooling resumes.

Question 14

The behaviour and processes that govern the textures of magmatic rocks depend on the content of a magma's three distinct parts: ________.

A)andesite, basalt, and rhyolite
B)quartz, feldspar, and ferromagnesian minerals
C)solid, liquid, and gas
D)high pressure, medium pressure, and low pressure

Question 15

The last minerals to crystallize in Bowen's reaction series result in igneous rocks with a ________ composition.

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

Question 16

Magmas rise to shallower depths and intrude the crust or extrude on the surface because ________.

A)of buoyancy, the magmas are hotter and less dense than the surrounding rocks where they form
B)of centrifugal and tidal forces as the Earth spins
C)the pressure at depth is so great that the magmas are forced upwards
D)earthquakes shake the crust and allow the magma to escape upwards

Question 17

As melts cool their viscosity increases (they lose their mobility and get stiffer)even before they start to crystallize because ________.

A)all of the sodium and potassium escape
B)their ions become more disordered
C)the silica tetrahedra in the melt start to link up and make larger and stronger units
D)they increase in volume

Question 18

At about 100 km depth across most of the upper mantle, peridotite is about ________, which is very close to its melting temperature.

A)800°C to 1000°C
B)1000°C to 1200°C
C)1200°C to 1400°C
D)1400°C to 1800°C

Question 19

What is/are thought to be the main mechanism(s)for generating basaltic melts from hot peridotite near its melting point in the upper mantle?

A)conductive heating of basaltic ocean crust subducted into the mantle
B)frictional heating of basaltic ocean crust as it slides down subduction zones
C)intrusion of hotter solid mantle rocks from below
D)drop of confining pressure or introduction of water

Question 20

Consider Bowen's reaction series.Which mineral would you expect to see as a phenocryst in a porphyritic basalt?

A)olivine
B)quartz
C)orthoclase
D)sodium-rich plagioclase

Question 21

Intermediate rocks like andesite and diorite ________.

A)are major constituents of the oceanic crust
B)rarely contain plagioclase feldspar, pyroxenes or amphiboles
C)form mainly in convergent continental margins
D)contain the semiprecious gems beryl, topaz, and tourmaline

Question 22

The classification and nomenclature of igneous rocks is based primarily on ________.

A)Aristotelian logic
B)colour and weight
C)mineral composition and proportions along with textures that give environmental conditions of crystallization
D)where the rock was found and the local names for this in different languages

Question 23

Which igneous rock or magma has the lowest silica (SiO?)content?

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

Question 24

Changing the composition of magma by incorporating surrounding host rock is known as ________.

A)magma mixing
B)partial melting
C)differentiation
D)assimilation

Question 25

Which of the following igneous rocks is composed mainly of ferromagnesian minerals with less than 20% feldspar?

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

Question 26

Felsic rocks have silica contents of ________ are rich in ________.

A)under 40%, olivine and pyroxene
B)around 50%, pyroxene and plagioclase feldspar
C)about 70%, quartz and feldspar
D)more than 85%, calcium rich feldspars and amphiboles

Question 27

The most abundant elements in common crustal igneous rocks are ________.

A)calcium and sodium
B)iron and magnesium
C)oxygen and silicon
D)granite and basalt

Question 28

The mechanism of selectively removing the minerals which melt at the lowest temperature is ________.

A)assimilation
B)magmatic differentiation
C)magma mixing
D)partial melting

Question 29

Which of the following igneous rocks is thought to be common in the Earth's mantle but rare in the crust?

A)pumice
B)granite
C)pegmatite
D)peridotite

Question 30

Felsic rocks like granite ________.

A)are major constituents of the continental crust
B)are extremely rare on Earth but abundant on the Moon
C)form mainly in volcanic island chains
D)make up most of the ocean floor and volcanic island chains

Question 31

Mafic rocks have silica contents of ________ and are mainly composed of ________.

A)under 40%, olivine and pyroxene
B)around 50%, pyroxene and plagioclase feldspar
C)up to 70% quartz and feldspar
D)more than 85%, potassium rich feldspars and micas

Question 32

As the silica content varies from less than 40% to more than 70% there is a systematic ________.

A)decrease in calcium, magnesium, and iron with an increase in sodium and potassium
B)increase in calcium, magnesium, and iron with a decrease in sodium and potassium
C)increase in the temperature at which point melting begins
D)decrease in the quartz content of the rocks

Question 33

While the ultramafic rock, peridotite, comprises the bulk of the mantle, the earth hasn't been hot enough to make much ________ (its volcanic equivalent)since the Precambrian.

A)andesite
B)gabbro
C)komatiite
D)welded tuff

Question 34

Which of the following is the dominant feldspar in basalt?

A)plagioclase
B)microcline
C)orthoclase
D)pyroxene

Question 35

What weight percentage of silica (SiO?)typifies granites and rhyolites?

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

Question 36

Which of the following minerals crystallize early in Bowen's reaction series?

A)biotite
B)quartz
C)olivine
D)muscovite

Question 37

Mafic rocks like basalt and gabbro ________.

A)are major constituents of the continental crust
B)are very low in their iron and magnesium contents
C)form mainly in continental mountain belts
D)make up most of the ocean floor and volcanic island chains

Question 38

98% of most common crustal igneous rocks are made of ________.

A)oxygen, silicon, aluminum, calcium, sodium, potassium, magnesium, and iron
B)oxygen, hydrogen, nitrogen carbon, and sulfur
C)titanium, manganese, gold, silver, and uranium
D)lithium, cesium, uranium, and rare earths

Question 39

The most common ferromagnesian silicate minerals by % in igneous rocks are ________.

A)aragonite, barite, calcite, and diamond
B)feldspar, quartz, and muscovite
C)magnetite, chromite, hematite, and ilmenite
D)olivine, pyroxene, amphibole, and biotite

Question 40

The most common non-ferromagnesian silicate minerals (>40 %)in most igneous rocks are ________.

A)calcite
B)feldspar
C)olivine
D)quartz

Question 41

Match the description with the appropriate texture.
A.aphanitic B.porphyritic C.phaneritic D.glass
________ a magnifying glass or microscope is needed to see individual mineral grains

Question 42

A ________ is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly liquid.

A)porphyrocryst
B)vesicle
C)phenocryst
D)xenocryst

Question 43

How long does it take for a large magma body at great depth to cool and completely crystallize?

A)a few days
B)a few months
C)several years
D)several tens to a hundreds of thousands of years

Question 44

Match the description with the appropriate texture.
A.aphanitic B.porphyritic C.phaneritic D.glass
________ mineral grains are of roughly equal size and coarse enough to be seen without a microscope or magnifying glass

Question 45

Which magma is most likely to quench (congeal)to a natural glass?

A)highly viscous; cools quickly
B)highly viscous; cools slowly
C)highly fluid; cools slowly
D)highly fluid; cools quickly

Question 46

Match the description with the appropriate texture.
A.aphanitic B.porphyritic C.phaneritic D.glass
________ magma cools and consolidates without growth of mineral grains

Question 47

What are vesicles?

A)open voids in an igneous rock left when phenocrysts dissolved away
B)the larger mineral grains of a porphyritic texture
C)the fragments comprising a volcanic breccia
D)open spaces formed in the rock as the lava solidified around gas bubbles

Question 48

Rocks that consist completely of disordered ions with no long range structures are called ________.

A)aphanitic
B)glassy
C)phaneritic
D)porphyritic

Question 49

The size, shape, and geometric arrangement of mineral grains in igneous rocks is called ________ and it indicates ________.

A)aphanitic form, how much water was present in the melt
B)igneous geometry, the original % of partial melting
C)geomorphology, depth of origin for the original magma
D)texture, the environmental conditions in which the rock formed

Question 50

Lava flows are typically finer grained than intrusive igneous rocks.Why?

A)Intrusive magma is cooler because it is well insulated by the surrounding rock.
B)Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow.
C)The extrusive magma cools quickly so the mineral grains do not have time to grow.
D)The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.

Question 51

Which of the following best describes an aphanitic texture?

A)The rock is crystalline; mineral grains are too small to be visible without a magnifying lens or microscope.
B)The mineral grains have glassy textures.
C)The rock consists of broken, volcanic-rock and mineral fragments.
D)The rock is crystalline; mineral grains are of distinctly different sizes.

Question 52

Match the description with the appropriate texture.
A.aphanitic B.porphyritic C.phaneritic D.glass
________ rock has two or more, distinctly different-sized populations of mineral grains

Question 53

Name the texture that requires a magnifying glass or microscope to see individual mineral grains.

A)aphanitic
B)porphyritic
C)phaneritic
D)pegmatitic

Question 54

A(n)________ texture would be most unlikely to occur in an extrusive igneous rock.

A)pyroclastic
B)glassy
C)aphanitic
D)phaneritic

Question 55

Which igneous texture indicates two, distinctly different sizes of mineral grains?

A)aphanitic
B)porphyritic
C)phaneritic
D)glassy

Question 56

Vesicles are ________.

A)cavities or bubble-shaped holes formed in lavas or pyroclastics by escaping gases during quenching
B)empty pits where large crystals like phenocrysts weathered out during exposure
C)holes that used to be full of hot liquid water when the rocks erupted
D)the sex organs of fossilized creatures that once lived in the molten magma

Question 57

Which of the following are used for studying rocks with a polarizing microscope?

A)polished cubes
B)broken chips
C)thin sections
D)grain karats

Question 58

The main factors which directly govern the development of texture in all igneous rocks are ________.

A)buoyancy, crystal settling, and partial melting
B)cooling rate, dissolved volatiles, and silica content
C)volcano or pluton size and shape
D)weathering and climate

Question 59

Light coloured aphanitic rocks ________.

A)always form deep in the crust
B)consist predominantly of small non-ferromagnesian minerals
C)never form at the surface of the Earth
D)consist predominantly of large ferromagnesian minerals

Question 60

In what texture are mineral grains of roughly equal size and coarse enough to be seen without a microscope or magnifying glass?

A)phaneritic
B)aphanitic
C)pegmatitic
D)porphyritic

Question 61

Which of the following igneous rock always has a pyroclastic texture?

A)rhyolitic tuff
B)porphyritic basalt flow
C)intrusive granite pluton
D)andesitic lava flow

Question 62

In a porphyritic volcanic rock, which mineral grains are the last to crystallize?

A)phenocrysts
B)vesicles
C)pegmatites
D)matrix or groundmass

Question 63

When a rock has a two-stage cooling history (slow then fast)or has minerals that crystallized at different temperatures and grew at different rates it is ________.

A)aphanitic
B)phaneritic
C)porphyritic
D)pyroclastic

Question 64

The aphanitic equivalent of peridotite is

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

Question 65

The phaneritic equivalent of basalt is

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

Question 66

Visible quartz and potassium feldspar grains are the main constituents in which igneous rock?

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

Question 67

Exceptionally coarse grained felsic plutonic rocks that are rich in rare minerals and trace elements are probably ________.

A)pegmatites
B)obsidians
C)porphyrys
D)welded tuffs

Question 68

________ is a volcanic rock that is extremely vesicular and glassy.

A)Obsidian
B)Pegmatite
C)Tuff
D)Pumice

Question 69

What is the rock colour (total % of dark minerals)of a typical granite or rhyolite?

A)< 25%
B)25-45%
C)45-85%
D)> 85%

Question 70

The aphanitic equivalent of granite is

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

Question 71

When magma cools and consolidates without growth of mineral grains, it is

A)glassy
B)aphanitic
C)phaneritic
D)porphyritic

Question 72

What is the rock colour (total % of dark minerals)of a typical gabbro or basalt?

A)45-85%
B)< 25%
C)25-45%
D)> 85%

Question 73

Which texture would be most unlikely to occur in an extrusive igneous rock?

A)pyroclastic
B)glassy
C)aphanitic
D)phaneritic

Question 74

What phenocryst minerals would you expect to find in a porphyritic andesite?

A)intermediate (Ca-Na)plagioclase and amphibole or pyroxene
B)Na-rich plagioclase and K-feldspar
C)Ca-rich plagioclase and olivine
D)muscovite and biotite

Question 75

The aphanitic equivalent of diorite is

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

Question 76

Which of the following igneous rocks usually exhibit aphanitic texture?

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

Question 77

What do pumice and obsidian have in common?

A)basaltic composition
B)glassy texture
C)ultramafic composition
D)phaneritic texture

Question 78

Which of the following has the same mineral composition as andesite?

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

Question 79

________ typically exhibit pyroclastic textures.

A)Granites
B)Gabbros
C)Diorites
D)Welded tuffs

Question 80

Which of the following igneous rocks exhibit phaneritic texture?

A)granite; tuff
B)tuff; breccia
C)basalt; pumice
D)diorite; gabbro