Deck 3: Igneous Rocks and Processes

Question 1

In an igneous rock with two distinct classes of crystal size, which of the following is true?

A) The rock cooled quickly at first, but then the cooling process slowed down.
B) There was an explosion producing different sized crystals.
C) The rock cooled slowly at first, but then the cooling process speeded up.
D) The minerals were all large, but then some melted.

Answer 1

C

Question 2

An ultramafic rock has the highest proportion of:

A) iron and aluminum.
B) potassium and aluminum.
C) iron and magnesium.
D) oxygen and silicon.

Answer 2

C

Question 3

The two properties used most to classify igneous rocks are:

A) the grain size and the number of different minerals present.
B) color and mineral composition.
C) color and texture.
D) texture and mineral composition.

Answer 3

D

Question 4

Diorite is an example of an:

A) extrusive felsic rock.
B) extrusive intermediate rock.
C) intrusive intermediate rock.
D) intrusive felsic rock.

Question 5

An ultramafic igneous rock is one that contains about how much silica?

A) Greater than 65%.
B) 55% to 65%.
C) Less than 40%.
D) 45% to 55%.

Question 6

Which is a common rock found on both the Moon and the Earth?

A) Andesite.
B) Granite.
C) Basalt.
D) Rhyolite.

Question 7

Viscosity of a magma:

A) decreases with increasing temperature.
B) increases with decreasing temperature and high silica content.
C) increases with increasing temperature and low silica content.
D) decreases with increasing silica content.

Question 8

What is the process by which a single parent magma can produce a variety of rocks of different composition?

A) Assimilation.
B) Fractional crystallization.
C) Subduction.
D) Magma mixing.

Question 9

As the rate of cooling decreases, particle size in an igneous rock:

A) can not predict.
B) stays the same.
C) increases.
D) decreases.

Question 10

Which of the following statements concerning batholiths is NOT true?

A) They commonly consist of the mafic intrusive rock gabbro.
B) They often form the cores of mountain ranges.
C) They are at least 100 square kilometers (40 square miles) in surface area.
D) They are massive discordant igneous bodies.

Question 11

Most igneous rocks are composed primarily of:

A) oxygen and hydrogen.
B) oxygen and silicon.
C) iron and aluminum.
D) iron and magnesium.

Question 12

At the Earth's surface, the mineral albite melts at 1118° C. At a depth of 100 km, it would melt at:

A) 900^° C.
B) 1100^° C.
C) 1440^° C.
D) 750^° C.

Question 13

Which process accounts for the vast areas of intermediate and felsic rock seen in nature?

A) Crystal settling.
B) Intrusion.
C) Magma mixing.
D) Extrusion.

Question 14

Which of the following rocks probably underwent the slowest cooling rate?

A) Obsidian.
B) Pumice.
C) Gabbro.
D) Basalt.

Question 15

The term texture refers to:

A) the kinds of minerals that constitute the rock.
B) the appearance of irregularities on the rock surface.
C) the size and shape of the mineral components.
D) whether the rock feels smooth or gritty.

Question 16

Under which of the following conditions would rocks melt at a lower temperature?

A) Low water content, low pressure.
B) High water content, low pressure.
C) High water content, high pressure.
D) Low water content, high pressure.

Question 17

An igneous structure produced by deep- seated, extremely gaseous, highly explosive eruptions is:

A) a diapir.
B) a batholith.
C) a dike.
D) a diatreme.

Question 18

All of the following processes contribute felsic material to rising basaltic magmas EXCEPT:

A) melting of accumulated biogenic silica from marine microorganisms.
B) subduction zone magmas assimilate overlying crustal rocks.
C) melting of accumulated detrital continental sediments.
D) partial melting of the warm mantle above a subducting oceanic slab.

Question 19

Which of the statements regarding economically valuable igneous rocks or minerals is NOT true?

A) The fact that they crystallize at lower temperatures than most other minerals accounts for economically valuable concentrations of some minerals.
B) Solution and hot fluid redeposition form economically valuable concentrations of some minerals.
C) Valuable stones, such as emerald and topaz, are found in felsic pegmatitic rock.
D) Gold, silver, copper, lead, and zinc often form near mafic and ultramafic igneous rocks.

Question 20

Which of the following is an example of a mafic igneous rock?

A) Gabbro.
B) Andesite.
C) Granite.
D) Rhyolite.

Question 21

The primary difference between magma and lava is that:

A) they are produced from different parent materials.
B) magma becomes lava anytime it is in a cooling condition.
C) one occurs at divergent plate boundaries, the other at convergent plate boundaries.
D) one is below the ground, the other is above the ground.

Question 22

Continental Basalts are frequently found:

A) where rifts open old continental plates.
B) above oceanic hot spots.
C) near colliding continental plates.
D) along transform plate boundaries.

Question 23

Which of the following is NOT true about Bowen's reaction series?

A) It shows how silicate minerals form as temperature decreases.
B) It shows how a complete range of igneous rock compositions may be formed from the same basaltic magma.
C) It shows that minerals never form in the same order.
D) It shows that minerals form in a definite sequence.

Question 24

The rocks that make up the oceanic crust are all:

A) basalts and gabbros.
B) andesites and diorites.
C) aphanitic (rhyolites, andesites, and basalts) because they were cooled rapidly by ocean water.
D) rhyolites and granites.

Question 25

A domed intrusion of igneous rock produced by rising magma is termed a:

A) country rock.
B) xenolith.
C) diapir.
D) dike.

Question 26

Plutonic rocks are characterized by which type of texture?

A) Glassy.
B) Aphanitic.
C) Phaneritic.
D) Vesicular.

Question 27

A phaneritic rock containing a relatively high percentage of silica is a:

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

Question 28

Which of the following statements concerning cooling magma is NOT true?

A) Different minerals crystallize at different temperatures.
B) Composition of the magma remains the same as it crystallizes.
C) Crystals grow until they touch the edges of other crystals.
D) As magma cools, new bonds form between ions.

Question 29

What features on Earth are indirectly the result of the melting of rocks?

A) Eroded mountains.
B) The oceans and atmosphere.
C) Landslides.
D) Earthquakes.

Question 30

As pressure increases, the melting- point of a rock:

A) can not predict.
B) stays the same.
C) decreases.
D) increases.

Question 31

The classification of intrusive igneous structures depends on all of the following EXCEPT:

A) orientation with country rock.
B) size.
C) shape.
D) composition and texture.

Question 32

Which of the following is an example of an intermediate igneous rock?

A) Peridotite.
B) Granite.
C) Basalt.
D) Andesite.

Question 33

All of the following are differences between MORBs and OIBs EXCEPT:

A) MORBs are composed of basalts, and OIBs are composed of gabbros.
B) MORBs probably formed from partial melting of the upper mantle, and OIBs probably formed from a deep part of the mantle.
C) MORBs contain less potassium and uranium than OIBs.
D) MORBs occur at divergent plate boundaries, and OIBs occur over hot spots.

Question 34

At the Battle of Gettysburg:

A) both were sills.
B) Seminary Ridge was a sill, Cemetary Ridge was a dike.
C) Seminary Ridge was a dike, Cemetary Ridge was a sill.
D) both were dikes.

Question 35

Obsidian is dark- colored because of its:

A) high concentrations of amphibole.
B) high concentration of iron and magnesium.
C) because it is a mafic rock.
D) minute iron minerals scattered throughout the glass.

Question 36

Fluid magma rises for all of the following reasons EXCEPT:

A) surrounding rocks press on the magma and squeeze it upward.
B) it is less dense than the solid rock that surrounds it.
C) gases in the magma expand outward, driving the magma upward.
D) the Earth's magnetic field acts on the iron component of the magma.

Question 37

The geothermal gradient describes how:

A) pressure increases with depth within the Earth.
B) temperature increases with depth within the Earth.
C) water content increases with depth within the Earth.
D) magma becomes more mafic with depth within the Earth.

Question 38

All of the following represent typical tectonic settings for the occurrence of the specified rock type EXCEPT:

A) granite at continental rifts.
B) andesite at subduction zones.
C) continental basalts at continental rifts.
D) rhyolite at subduction zones.

Question 39

A dike is a:

A) a discordant tabular pluton.
B) a discordant non- igneous body.
C) a massive discordant pluton.
D) a concordant tabular pluton.

Question 40

The temperature at which a mineral melts:

A) is the same temperature at which it crystallizes.
B) is higher than the temperature at which it crystallizes.
C) is lower than the temperature at which it crystallizes.
D) is much higher than the temperature at which it crystallizes.

Question 41

Which of the following statements about the creation of magma is true?

A) Increasing pressure raises the melting point except in the presence of water.
B) Increasing pressure raises the melting point regardless of the water content.
C) Increasing pressure lowers the melting point except in the presence of water.
D) Increasing pressure raises the melting point except in the absence of water.

Question 42

A sill is a:

A) a discordant tabular pluton.
B) a concordant tabular pluton.
C) a massive discordant pluton.
D) a massive concordant pluton.

Question 43

The texture of obsidian and pumice is:

A) phaneritic, resulting from slow cooling.
B) aphanitic, resulting from rapid cooling.
C) porphyritic, resulting from first slow, then rapid, cooling.
D) glassy, resulting from rapid cooling.

Question 44

List and define the two properties by which igneous rocks are classified.

Question 45

List and describe four economic uses for igneous rocks.

Question 46

Why do the terms aphanitic or phaneritic not apply to the texture of pumice or obsidian?

Question 47

Explain the correlation between Bowen's reaction series and various igneous rock compositions.

Question 48

An aphanitic mafic rock is a:

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

Question 49

Batholiths are primarily composed of intermediate and felsic compositions. A few ancient batholiths that formed several billion years ago are mafic. Why is this the case?

Question 50

Describe how the factors of heat, pressure, and water content influence the melting point temperature of crustal rocks.

Question 51

Where are most igneous rocks found?

A) Either within plates or at plate boundaries.
B) At or near plate boundaries.
C) Within plates.
D) No relationship exists.

Question 52

The fractional crystallization of mafic magmas into both mafic and felsic rocks cannot account for all the igneous rocks in existence. What other processes can be used to explain why felsic igneous rocks are so abundant?

Question 53

Why are basalt and gabbro the only igneous rocks in oceanic crust?

Question 54

What is the last mineral to form according to Bowen's reaction series?

A) Olivine.
B) Quartz.
C) Calcium plagioclase.
D) Muscovite.

Question 55

The existence of both intrusive and extrusive igneous rocks demonstrates that magma rises. Describe four reasons why magma rises.

Question 56

What is the origin of the two types of igneous rocks found on the Moon?

Question 57

A laccolith is a:

A) domed, concordant pluton.
B) massive discordant pluton.
C) saucer- shaped, concordant pluton.
D) discordant tabular pluton.