Deck 4: Igneous Rocks and Intrusive Activity

Question 1

A(n)texture represents a single, long period of cooling and crystallization.

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

Answer 1

C

Question 2

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 quickly
D)highly fluid; cools slowly

Answer 2

A

Question 3

Which of the following igneous rocks exhibit aphanitic texture?

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

Answer 3

C

Question 4

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

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

Question 5

is composed mainly of ferromagnesian minerals.

A)Rhyolite
B)Andesite
C)Granite
D)Peridotite

Question 6

All of the following are factors that affect the generation of magma EXCEPT for _ .

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

Question 7

Extrusive igneous rocks are typically finer grained than intrusive igneous rocks. Why?

A)The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.
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)Intrusive magma is cooler because it is well insulated by the surrounding rock.

Question 8

Which of the following igneous rocks has a pyroclastic texture?

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

Question 9

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

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

Question 10

often contain gem- quality crystals of minerals such as beryl and tourmaline and high concentrations of relatively rare elements such as lithium, boron, and beryllium?

A)Granitic pegmatites
B)Basaltic lavas
C)Diorite plutons
D)Welded tuff sheets

Question 11

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

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

Question 12

is a volcanic rock that is extremely vesicular and glassy.

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

Question 13

has the same mineral composition as andesite.

A)Diorite
B)Granite
C)Basalt
D)Gabbro

Question 14

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

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

Question 15

In which of the following igneous rocks and environments would you expect to find unusually high concentrations of rare elements such as lithium, beryllium, and boron?

A)pegmatite; crystallized from a water- rich, highly differentiated, residual magma
B)peridotite; crystallized at depth in the upper mantle
C)pumice lump; crystallized at depth in a mass of intrusive granite
D)basalt dike; fills a vertical fracture at shallow depth

Question 16

Which of the following best describes an aphanitic texture?

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

Question 17

is thought to be common in the Earth's mantle but rare in the crust.

A)Granite
B)Peridotite
C)Pumice
D)Pegmatite

Question 18

is characterized by very coarse mineral grains.

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

Question 19

What do pumice and obsidian have in common?

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

Question 20

The sizes, shapes, and arrangements of mineral grains in an igneous rock are known as _.

A)mineral content
B)texture
C)silica content
D)Bowen's reaction series

Question 21

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

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

Question 22

Pegmatites consist of what size mineral grains?

Question 23

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

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

Question 24

Visible quartz and potassium feldspar grains are the main constituents in a _.

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

Question 25

The last minerals to crystallize on Bowen's Reaction Series result in igneous rocks with a composition.

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

Question 26

is named for a prominent, volcanic mountain range in western South America.

A)Basalt
B)Andesite
C)Peridotite
D)Pegmatite

Question 27

is the dominant lava erupted from volcanoes on Hawaii and Iceland.

A)Basalt
B)Peridotite
C)Rhyolite
D)Andesite

Question 28

refers to the removal and isolation of early- formed mineral grains that can cause the composition of the remaining magma to change.

Question 29

What term denotes the larger mineral grains in a porphyritic igneous rock?

Question 30

is the name given to molten rock below the Earth's surface.

Question 31

Igneous rocks are classified on the basis of what two main characteristics?

Question 32

Name two igneous rocks with glassy textures.

Question 33

magma, commonly erupted along oceanic ridge systems, originates by partial melting of mantle peridotite.

Question 34

Which igneous rock or magma has the lowest silica (SiO2)content?

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

Question 35

A(n)texture refers to rocks composed mainly of mineral and volcanic fragments.

Question 36

Technically, the process whereby ions arrange themselves into orderly patterns during the cooling of a liquid is called .

Question 37

is the dominant feldspar in basalt.

A)Orthoclase
B)Plagioclase
C)Microcline
D)Pyroxene

Question 38

Melting of rocks to form magma as a result of decreases pressure is known as .

Question 39

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

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

Question 40

Pyroxene, hornblende, and biotite are all minerals found on the series of Bowen's Reaction Series.

Question 41

In general, what happens in terms of composition as crystallization proceeds down the Bowen's reaction?

Question 42

In a series of basaltic lava flows on Hawaii, the top and bottom of each flow is difficult to distinguish just by looking at the layers of rock. What are some rock characteristics (texture, mineralogy, etc.)and other features that you might use to recognize individual lava flows?

Question 43

The size of crystals in igneous rocks is generally a function of the rate of cooling. However, within the same rock, crystal size does not necessarily reflect the order of crystallization for individual minerals. Without using Bowen's Reaction Series, how might you determine the order of crystallization of minerals in an individual rock sample? (Hint: Think about the texture.)

Question 44

All other factors being equal (geothermal gradient, pressure, composition, and heat from other sources such as friction), why is magma generally produced in association with subduction zones as opposed to areas away from subduction zones?

Question 45

What magma- generating process is exhibited by the diagram below? When does this process take place?