ESS 101 B Laboratory 4 Quiz :
Volcanoes, Plutons, and Igneous
Rocks Questions and Answers
Latest 2026/2027 Solved 100%
Course
ESS 101
1. A large, intrusive igneous body that covers more than about 100 km² and commonly
forms the cores of mountain ranges is called a:
A. Sill
B. Batholith
C. Dike
D. Laccolith
Correct Answer: B. Batholith
Rationale: A batholith is a very large discordant plutonic body formed when magma crystallizes
deep within Earth's crust.
2. Which intrusive igneous structure cuts across pre-existing rock layers?
A. Sill
B. Laccolith
C. Dike
D. Lopolith
Correct Answer: C. Dike
Rationale: A dike is a tabular, discordant intrusion that cuts across the existing layers of
surrounding rock.
3. An intrusive igneous body that forms parallel to the surrounding rock layers is called a:
A. Dike
B. Sill
C. Volcanic neck
D. Batholith
Correct Answer: B. Sill
Rationale: A sill is a concordant intrusion that is emplaced parallel to pre-existing layers.
4. Which igneous texture indicates that magma cooled slowly beneath Earth's surface?
,A. Glassy
B. Aphanitic
C. Phaneritic
D. Vesicular
Correct Answer: C. Phaneritic
Rationale: Slow underground cooling gives mineral crystals enough time to grow large enough
to be seen without magnification.
5. An igneous rock containing large crystals surrounded by a fine-grained matrix has a:
A. Glassy texture
B. Porphyritic texture
C. Vesicular texture
D. Pyroclastic texture
Correct Answer: B. Porphyritic texture
Rationale: Porphyritic texture develops when magma experiences two stages of cooling,
producing large phenocrysts followed by finer-grained material.
6. Which texture develops when lava cools so rapidly that crystals have little or no time to
form?
A. Phaneritic
B. Porphyritic
C. Glassy
D. Pegmatitic
Correct Answer: C. Glassy
Rationale: Extremely rapid cooling can prevent atoms from arranging into crystals, producing
volcanic glass.
7. Which factor generally increases magma viscosity?
A. Higher temperature
B. Lower silica content
C. Higher silica content
D. Reduced crystal content
Correct Answer: C. Higher silica content
Rationale: Silica creates stronger molecular structures within magma, making high-silica
magma more resistant to flow.
8. Which magma composition generally has the lowest viscosity?
, A. Felsic
B. Intermediate
C. Mafic
D. Rhyolitic
Correct Answer: C. Mafic
Rationale: Mafic magma contains relatively little silica and is therefore generally hotter and less
viscous than felsic magma.
9. Which rock is the intrusive equivalent of basalt?
A. Granite
B. Diorite
C. Gabbro
D. Rhyolite
Correct Answer: C. Gabbro
Rationale: Basalt and gabbro have similar mafic compositions. Basalt forms extrusively,
whereas gabbro crystallizes slowly underground.
10. Which rock is the extrusive equivalent of granite?
A. Rhyolite
B. Basalt
C. Gabbro
D. Peridotite
Correct Answer: A. Rhyolite
Rationale: Granite and rhyolite are both felsic in composition. Granite is intrusive and rhyolite
is extrusive.
11. Which rock is the intrusive equivalent of andesite?
A. Gabbro
B. Diorite
C. Granite
D. Peridotite
Correct Answer: B. Diorite
Rationale: Diorite is an intermediate intrusive rock, while andesite is its intermediate volcanic
counterpart.
12. A volcanic rock containing abundant small holes produced by escaping gas bubbles is
described as:
Volcanoes, Plutons, and Igneous
Rocks Questions and Answers
Latest 2026/2027 Solved 100%
Course
ESS 101
1. A large, intrusive igneous body that covers more than about 100 km² and commonly
forms the cores of mountain ranges is called a:
A. Sill
B. Batholith
C. Dike
D. Laccolith
Correct Answer: B. Batholith
Rationale: A batholith is a very large discordant plutonic body formed when magma crystallizes
deep within Earth's crust.
2. Which intrusive igneous structure cuts across pre-existing rock layers?
A. Sill
B. Laccolith
C. Dike
D. Lopolith
Correct Answer: C. Dike
Rationale: A dike is a tabular, discordant intrusion that cuts across the existing layers of
surrounding rock.
3. An intrusive igneous body that forms parallel to the surrounding rock layers is called a:
A. Dike
B. Sill
C. Volcanic neck
D. Batholith
Correct Answer: B. Sill
Rationale: A sill is a concordant intrusion that is emplaced parallel to pre-existing layers.
4. Which igneous texture indicates that magma cooled slowly beneath Earth's surface?
,A. Glassy
B. Aphanitic
C. Phaneritic
D. Vesicular
Correct Answer: C. Phaneritic
Rationale: Slow underground cooling gives mineral crystals enough time to grow large enough
to be seen without magnification.
5. An igneous rock containing large crystals surrounded by a fine-grained matrix has a:
A. Glassy texture
B. Porphyritic texture
C. Vesicular texture
D. Pyroclastic texture
Correct Answer: B. Porphyritic texture
Rationale: Porphyritic texture develops when magma experiences two stages of cooling,
producing large phenocrysts followed by finer-grained material.
6. Which texture develops when lava cools so rapidly that crystals have little or no time to
form?
A. Phaneritic
B. Porphyritic
C. Glassy
D. Pegmatitic
Correct Answer: C. Glassy
Rationale: Extremely rapid cooling can prevent atoms from arranging into crystals, producing
volcanic glass.
7. Which factor generally increases magma viscosity?
A. Higher temperature
B. Lower silica content
C. Higher silica content
D. Reduced crystal content
Correct Answer: C. Higher silica content
Rationale: Silica creates stronger molecular structures within magma, making high-silica
magma more resistant to flow.
8. Which magma composition generally has the lowest viscosity?
, A. Felsic
B. Intermediate
C. Mafic
D. Rhyolitic
Correct Answer: C. Mafic
Rationale: Mafic magma contains relatively little silica and is therefore generally hotter and less
viscous than felsic magma.
9. Which rock is the intrusive equivalent of basalt?
A. Granite
B. Diorite
C. Gabbro
D. Rhyolite
Correct Answer: C. Gabbro
Rationale: Basalt and gabbro have similar mafic compositions. Basalt forms extrusively,
whereas gabbro crystallizes slowly underground.
10. Which rock is the extrusive equivalent of granite?
A. Rhyolite
B. Basalt
C. Gabbro
D. Peridotite
Correct Answer: A. Rhyolite
Rationale: Granite and rhyolite are both felsic in composition. Granite is intrusive and rhyolite
is extrusive.
11. Which rock is the intrusive equivalent of andesite?
A. Gabbro
B. Diorite
C. Granite
D. Peridotite
Correct Answer: B. Diorite
Rationale: Diorite is an intermediate intrusive rock, while andesite is its intermediate volcanic
counterpart.
12. A volcanic rock containing abundant small holes produced by escaping gas bubbles is
described as:
