Question 1

Magma that cools below Earth's surface form most of the volcanoes in North America.

Accepted Answer

A) True 
 B)False

Question 2

Volcanoes always erupt magmas of the same type.

Accepted Answer

A) True 
 B)False

Question 3

Rhyolite forms when a mafic magma cools on Earth's surface.

Accepted Answer

A) True 
 B)False

Question 4

Pegmatite refers to

Accepted Answer

A)   an extremely coarse texture
B)   an igneous rock body
C)   a felsic composition
D)   a mafic composition
E)   A and C

Question 5

Magmas formed at subduction zones are mostly intermediate or felsic.

Accepted Answer

A) True 
 B)False

Question 6

If early-formed crystals settled out of a magma, the magma would tend to be

Accepted Answer

A)   unchanged in composition.
B)   finer grained.
C)   enriched in silica.
D)   less viscous.
E)   water soluble.

Question 7

How do complex pegmatites differ from simple pegmatites?

Accepted Answer

Simple pegmatites are basicall...

Question 8

Natural glass such as obsidian forms when

Accepted Answer

A)   magma cools rapidly and very tiny crystals form.
B)   magma cools too rapidly for crystals to form.
C)   magma cools too slowly for crystals to form.
D)   magma doesn't cool.
E)   magma is reheated.

Question 9

Explain how we can tell, from a hand sample of an igneous rock, whether it formed as a volcanic rock or a plutonic rock?

Accepted Answer

If the texture is phaneritic, ...

Question 10

The magmas formed beneath spreading ridges are always felsic.

Accepted Answer

A) True 
 B)False

Question 11

Partial melting explains the origin and composition of magmas at spreading ridges but not subduction zones.

Accepted Answer

A) True 
 B)False

Question 12

Ultramafic rocks are ___________found at the Earth's surface.

Accepted Answer

The answer of Ultramafic rocks are ___________found at the Earth's...

Question 13

Describe the role silica plays in controlling viscosity.

Accepted Answer

The bonds formed by ...

Question 14

A granite would form under conditions that included

Accepted Answer

A)   a mafic magma cooling in the subsurface.
B)   a felsic magma cooling in the subsurface.
C)   a mafic magma cooling on Earth's surface.
D)   a felsic magma cooling on Earth's surface.
E)   none of the above. B

Question 15

A magma composed of more than 65% silica is referred to as

Accepted Answer

A)   mafic
B)   intrusive
C)   intermediate
D)   extrusive
E)   felsic E

Question 16

Batholiths typically contain

Accepted Answer

A)   phaneritic rocks composed predominantly of ferromagnesium silicates.
B)   aphanitic rocks composed predominantly of ferromagnesium silicates.
C)   phaneritic rocks composed predominantly of non-ferromagnesium silicates.
D)   aphanitic rocks composed predominantly of non-ferromagnesium silicates.
E)   none of the above.

Question 17

Magma that is forcefully ejected into the atmosphere as particles is known as

Accepted Answer

A)   pyroclastic material
B)   lava flow
C)   aphanitic
D)   dike rock
E)   plutonic

Question 18

Volcanic necks form when

Accepted Answer

A)   the magma abruptly cools into a solid rock column during the initial eruption
B)   the eruptive material is eroded from the flanks of the volcanic pipe
C)   dikes are exposed at earth's surface
D)   lava fountains cool on steep volcanic slopes
E)   the country rock surrounding a small stock is eroded

Question 19

Geologists generally agree that batholiths are emplaced by forceful injection.

Accepted Answer

A) True 
 B)False

Question 20

Laccoliths are more similar to sills than they are to dikes.

Accepted Answer

A) True 
 B)False  True

Exam 4: Igneous Rocks and Intrusive Igneous Activity

Magma that cools below Earth's surface form most of the volcanoes in North America.

Correct AnswerverifiedShow Answer

Volcanoes always erupt magmas of the same type.

Correct AnswerverifiedShow Answer

Rhyolite forms when a mafic magma cools on Earth's surface.

Correct AnswerverifiedShow Answer

Pegmatite refers to

Correct AnswerverifiedShow Answer

Magmas formed at subduction zones are mostly intermediate or felsic.

Correct AnswerverifiedShow Answer

If early-formed crystals settled out of a magma, the magma would tend to be

Correct AnswerverifiedShow Answer

How do complex pegmatites differ from simple pegmatites?

Correct AnswerverifiedSimple pegmatites are basicall...View AnswerShow Answer

Natural glass such as obsidian forms when

Correct AnswerverifiedShow Answer

Explain how we can tell, from a hand sample of an igneous rock, whether it formed as a volcanic rock or a plutonic rock?

Correct AnswerverifiedIf the texture is phaneritic, ...View AnswerShow Answer

The magmas formed beneath spreading ridges are always felsic.

Correct AnswerverifiedShow Answer

Partial melting explains the origin and composition of magmas at spreading ridges but not subduction zones.

Correct AnswerverifiedShow Answer

Ultramafic rocks are ___________found at the Earth's surface.

Correct AnswerverifiedShow Answer

Describe the role silica plays in controlling viscosity.

Correct AnswerverifiedThe bonds formed by ...View AnswerShow Answer

A granite would form under conditions that included

Correct AnswerverifiedB

A magma composed of more than 65% silica is referred to as

Correct AnswerverifiedE

Batholiths typically contain

Correct AnswerverifiedShow Answer

Magma that is forcefully ejected into the atmosphere as particles is known as

Correct AnswerverifiedShow Answer

Volcanic necks form when

Correct AnswerverifiedShow Answer

Geologists generally agree that batholiths are emplaced by forceful injection.

Correct AnswerverifiedShow Answer

Laccoliths are more similar to sills than they are to dikes.

Correct AnswerverifiedTrue

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Simple pegmatites are basicall...
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If the texture is phaneritic, ...
View Answer

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The bonds formed by ...
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B

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E

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True