ESS 101 A LAB 3: IGNEOUS ROCKS AND
PROCESSES QUESTIONS AND
ANSWERS 2026/2027 UPDATE || 100%
GUARANTEED PASS
1. Which of the following textures indicates a two-stage cooling history, where magma cooled
slowly at depth before being erupted and cooling rapidly?
A. Phaneritic
B. Aphanitic
C. Porphyritic
D. Glassy
Answer: C
Conceptual Explanation: Porphyritic texture features large crystals (phenocrysts) formed
at depth and a fine-grained groundmass formed during rapid surface cooling.
2. In Bowen’s Reaction Series, which mineral is the first to crystallize from a cooling mafic
melt in the discontinuous series?
A. Quartz
B. Olivine
C. Biotite
,D. Pyroxene
Answer: B
Conceptual Explanation: Olivine crystallizes at the highest temperatures, making it the
first mineral to form in the discontinuous branch of Bowen’s Reaction Series.
3. A discordant igneous body that cuts across pre-existing rock layers is known as a:
A. Sill
B. Laccolith
C. Dike
D. Batholith
Answer: C
Conceptual Explanation: Dikes are tabular, discordant intrusive bodies that cut across the
layering of the country rock.
4. Which process is primarily responsible for magma generation at mid-ocean ridges?
A. Decompression melting
B. Flux melting
C. Heat transfer melting
D. Assimilation
Answer: A
, Conceptual Explanation: As tectonic plates pull apart, the underlying mantle rises and
experiences a decrease in pressure, triggering decompression melting.
5. Which igneous rock has the same chemical composition as diorite but exhibits an aphanitic
texture?
A. Rhyolite
B. Andesite
C. Basalt
D. Gabbro
Answer: B
Conceptual Explanation: Andesite is the extrusive (aphanitic) equivalent of the
intermediate intrusive rock diorite.
6. The presence of vesicles in an igneous rock suggests that:
A. The magma cooled extremely slowly.
B. The rock was formed deep within the Earth’s crust.
C. Gas bubbles were trapped in the lava as it solidified.
D. The rock underwent high-grade metamorphism.
Answer: C
Conceptual Explanation: Vesicles are small cavities formed by gas bubbles escaping from
lava during solidification.
PROCESSES QUESTIONS AND
ANSWERS 2026/2027 UPDATE || 100%
GUARANTEED PASS
1. Which of the following textures indicates a two-stage cooling history, where magma cooled
slowly at depth before being erupted and cooling rapidly?
A. Phaneritic
B. Aphanitic
C. Porphyritic
D. Glassy
Answer: C
Conceptual Explanation: Porphyritic texture features large crystals (phenocrysts) formed
at depth and a fine-grained groundmass formed during rapid surface cooling.
2. In Bowen’s Reaction Series, which mineral is the first to crystallize from a cooling mafic
melt in the discontinuous series?
A. Quartz
B. Olivine
C. Biotite
,D. Pyroxene
Answer: B
Conceptual Explanation: Olivine crystallizes at the highest temperatures, making it the
first mineral to form in the discontinuous branch of Bowen’s Reaction Series.
3. A discordant igneous body that cuts across pre-existing rock layers is known as a:
A. Sill
B. Laccolith
C. Dike
D. Batholith
Answer: C
Conceptual Explanation: Dikes are tabular, discordant intrusive bodies that cut across the
layering of the country rock.
4. Which process is primarily responsible for magma generation at mid-ocean ridges?
A. Decompression melting
B. Flux melting
C. Heat transfer melting
D. Assimilation
Answer: A
, Conceptual Explanation: As tectonic plates pull apart, the underlying mantle rises and
experiences a decrease in pressure, triggering decompression melting.
5. Which igneous rock has the same chemical composition as diorite but exhibits an aphanitic
texture?
A. Rhyolite
B. Andesite
C. Basalt
D. Gabbro
Answer: B
Conceptual Explanation: Andesite is the extrusive (aphanitic) equivalent of the
intermediate intrusive rock diorite.
6. The presence of vesicles in an igneous rock suggests that:
A. The magma cooled extremely slowly.
B. The rock was formed deep within the Earth’s crust.
C. Gas bubbles were trapped in the lava as it solidified.
D. The rock underwent high-grade metamorphism.
Answer: C
Conceptual Explanation: Vesicles are small cavities formed by gas bubbles escaping from
lava during solidification.
