Geology 1 Questions for Chapter 4 1) Lava flows are typically finer ...

Geology 1 Questions for Chapter 4
1) 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.
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 slowly
D) highly fluid; cools quickly
3) The sizes, shapes, and arrangements of mineral grains in an igneous rock is known as ________.
A) silica content
B) texture
C) mineral content
D) Bowen's reaction series
Match the following rocks to their equivalent aphanitic or phaneritic igneous rocks.
A. aphanitic ! B. porphyritic ! C. phaneritic ! D. glassy
4) ________ magma cools and consolidates without growth of mineral grains
5) ________ mineral grains are of roughly equal size and coarse enough to be seen without a microscope or
magnifying glass
6) ________ rock has two or more distinctly different-sized populations of mineral grains
7) ________ a magnifying glass or microscope is needed to see individual mineral grains
8) 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
9) Consider the 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
Match the following rocks to their equivalent aphanitic or phaneritic igneous rocks.
A. andesite ! B. gabbro ! C. rhyolite
10) ________ granite
11) ________ basalt
11) ________ basalt
12) ________ diorite

13) Which of the following igneous rocks exhibit aphanitic texture?
A) granite; gabbro
B) andesite; rhyolite
C) andesite; diorite
D) rhyolite; gabbro
14) In a porphyritic volcanic rock, which mineral grains are the last to crystallize?
A) phenocrysts
B) vesicles
C) pegmatites
D) matrix or groundmass
The correct answer is 'D'.
Phenocrysts are the first
minerals to crystallize.
15) Visible quartz and potassium feldspar grains are the main constituents in a ________.
A) granite
B) gabbro
C) basalt
D) rhyolite
16) Which of the following igneous rocks has a pyroclastic texture?
A) rhyolitic tuff
B) porphyritic basalt
C) intrusive granite
D) andesitic lava
17) ________ is a volcanic rock that is extremely vesicular and glassy.
A) Obsidian
B) Pegmatite
C) Tuff
D) Pumice
18) ________ is composed mainly of ferromagnesian minerals.
A) Peridotite
B) Rhyolite
C) Andesite
D) Granite
19) Which of the following minerals crystallize early in Bowen's reaction series?
A) biotite
B) quartz
C) olivine
D) muscovite
20) ________ is the dominant feldspar in basalt.
A) Plagioclase
B) Microcline
C) Orthoclase
D) Pyroxene
21) 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

22) ________ is characterized by very coarse mineral grains?
A) Obsidian
B) Pumice
C) Pegmatite
D) Granite
23) A (an) ________ texture represents a single, long period of cooling and crystallization.
A) glassy
B) pyroclastic
C) aphanitic
D) phaneritic
24) ________ has the same mineral composition as andesite.
A) Basalt
B) Granite
C) Gabbro
D) Diorite
25) What do pumice and obsidian have in common?
A) basaltic composition
B) glassy texture
C) ultramafic composition
D) phaneritic texture
26) 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.
27) A ________ texture would be most unlikely to occur in an extrusive igneous rock.
A) pyroclastic
B) glassy
C) aphanitic
D) phaneritic
Should be 'D' since extrusive rock generally
have fine grained or apanitic texture and are
therefore unllikely to have phaneritic texture.
28) ________ is named for a prominent, volcanic mountain range in western South America.
A) Basalt
B) Andesite
C) Pegmatite
D) Peridotite
29) ________ is the dominant lava erupted from volcanoes on Hawaii and Iceland.
A) Rhyolite
B) Andesite
C) Peridotite
D) Basalt
30) Which igneous rock or magma has the lowest silica (SiO2) content?
A) granite
B) basalt
C) andesite
D) peridotite

31) ________ is thought to be common in the Earth's mantle but rare in the crust.
A) Pumice
B) Granite
C) Pegmatite
D) Peridotite
32) ________ 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) Welded tuff sheets
B) Basaltic lavas
C) Granitic pegmatites
D) Diorite plutons
33) The last minerals to crystallize on Bowen's Reaction Series result in igneous rocks with a ________ composition.
A) felsic
B) intermediate
C) mafic
D) ultramafic
34) Changing the composition of magma by incorporating surrounding host rock is known as ________.
A) magma mixing
B) partial melting
C) differentiation
D) assimilation
35) All of the following are factors that affect the generation of magma except for ________.
A) heat
B) pressure
C) crystal size
D) volatiles