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

Accepted Answer

Andesite is a fine-grained, intermediate igneous rock, which means it has a mineral composition between mafic and felsic rocks and is typically formed from the cooling of lava at the surface or near the surface, leading to its fine-grained texture.

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

Accepted Answer

Gabbro and basalt have the same chemical composition; gabbro is the intrusive (cooled slowly beneath the Earth's surface) counterpart, while basalt is the extrusive (cooled quickly at or near the Earth's surface) counterpart.

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

Accepted Answer

Porphyry is characterized by large crystals, known as phenocrysts, embedded in a fine-grained matrix. The description of 10-millimeter-long plagioclase crystals set in a fine-grained matrix matches the typical texture of porphyritic rocks.

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

Accepted Answer

James Hutton is credited with figuring out the origin of granite, marking a significant contribution to the understanding of geological processes and the formation of rocks.

Question 5

What is the approximate silica content of granite?
A)30%
B)50%
C)70%
D)90%

Accepted Answer

Granite is an igneous rock that typically contains about 70% silica (SiO2). This high silica content is what gives granite its strength and durability, making it a popular choice for construction and decorative purposes.

Question 6

Which of the following igneous rocks has the lowest silica content?
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

Ultramafic rocks have the lowest silica content among the options given. They are composed primarily of mafic minerals such as olivine and pyroxene, which contain less silica compared to minerals found in felsic, intermediate, or mafic rocks.

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

Accepted Answer

Grain size in igneous rocks is determined by the rate of cooling, not by the chemical composition. Fast cooling results in small grains, while slow cooling results in larger grains.

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.

Accepted Answer

Gabbro has a higher melting temperature than granite because it is a mafic rock, which means it is richer in magnesium and iron compared to granite, which is a felsic rock higher in silica. This composition difference leads to gabbro having a higher melting temperature.

Question 9

Which of the following minerals is rarely found in felsic igneous rocks?
A)olivine
B)orthoclase feldspar
C)plagioclase feldspar
D)quartz

Accepted Answer

Olivine is a mineral typically found in mafic and ultramafic igneous rocks, not in felsic igneous rocks. Felsic rocks, which are rich in silica, commonly contain minerals such as orthoclase feldspar, plagioclase feldspar, and quartz, making olivine rare in such compositions.

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

Accepted Answer

Tuff is a type of rock formed from volcanic ash ejected during explosive volcanic eruptions. The ash settles and, over time, becomes lithified or compacted and cemented into solid rock.

Question 11

Which of the following igneous rocks crystallizes at Earth's surface?
A)basalt
B)gabbro
C)granite
D)peridotite

Accepted Answer

Basalt is an igneous rock that crystallizes at Earth's surface, typically forming from lava flows that cool rapidly.

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

Accepted Answer

Pumice is characterized by a large number of vesicles, which are formed by the escape of volcanic gases during the rapid cooling and solidification of lava. These vesicles give pumice its light, porous texture.

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

Accepted Answer

Rhyolite is a fine-grained igneous rock that is rich in silica, distinguishing it from other types of igneous rocks by its composition and texture.

Question 14

Andesite is an example of a(n)__________ igneous rock.
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

Andesite is an example of an intermediate igneous rock, characterized by an intermediate silica content compared to felsic and mafic rocks.

Question 15

Which of the following igneous rocks does not consist of volcanic glass?
A)ash
B)gabbro
C)obsidian
D)pumice

Accepted Answer

Gabbro is an intrusive igneous rock, meaning it forms from magma that cools slowly beneath the Earth's surface, allowing large crystals to form. It does not consist of volcanic glass, unlike obsidian and pumice, which are extrusive igneous rocks formed from rapid cooling of lava, and ash, which is a product of volcanic eruptions.

Question 16

Which of the following types of igneous rocks are rarely found as lavas?
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

Ultramafic rocks are rarely found as lavas because their high magnesium and iron content makes them have a very high melting point, which means they are more commonly found in the Earth's mantle rather than as surface lava flows.

Question 17

Felsic igneous rocks contain abundant __________ silicate minerals.
A)double-chain
B)framework
C)isolated tetrahedra
D)single-chain

Accepted Answer

Felsic igneous rocks are rich in silica and contain abundant framework silicate minerals, which have a three-dimensional network of silica tetrahedra.

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

Accepted Answer

Plagioclase feldspar is a common mineral in both felsic and mafic igneous rocks, serving as a key component across a wide range of rock types due to its presence in both silica-rich and silica-poor environments.

Question 19

Which of the following igneous rocks has the same chemical composition as basalt?
A)andesite
B)diorite
C)gabbro
D)rhyolite

Accepted Answer

Gabbro and basalt have the same chemical composition but differ in their crystal sizes. Gabbro has larger crystals due to slower cooling, typically occurring beneath the Earth's surface, while basalt, with its smaller crystals, cools quickly at or near the surface.

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

Accepted Answer

Largest crystals in a lava flow are typically found near or just below the center of the flow, where cooling rates are slower, allowing more time for crystal growth.

Quiz 4: Igneous Rocks: Solids From Melts

Which of the following best describes an andesite?

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

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?

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

What is the approximate silica content of granite?

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

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

Which of the following statements is true?

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

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

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

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

Which of the following best describes a rhyolite?

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

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

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

Felsic igneous rocks contain abundant __________ silicate minerals.

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

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

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