ESS 101 A LAB 4: IGNEOUS PROCESSES
AND VOLCANISM QUESTIONS AND
ANSWERS 2026/2027 UPDATE || 100%
GUARANTEED PASS
1. Which mineral is the first to crystallize in the discontinuous branch of Bowen’s Reaction
Series?
A. Quartz
B. Biotite
C. Olivine
D. Pyroxene
Answer: C
Conceptual Explanation: Olivine is the first mineral to crystallize at the highest
temperatures in the discontinuous series.
2. What texture is characterized by two distinct sizes of crystals, indicating two stages of
cooling?
A. Aphanitic
B. Phaneritic
C. Porphyritic
,D. Glassy
Answer: C
Conceptual Explanation: Porphyritic texture indicates a period of slow cooling followed
by rapid cooling, creating large phenocrysts in a fine-grained groundmass.
3. Which igneous rock has a felsic composition and a phaneritic texture?
A. Granite
B. Rhyolite
C. Basalt
D. Gabbro
Answer: A
Conceptual Explanation: Granite is a coarse-grained (phaneritic) intrusive rock with a
high silica (felsic) content.
4. What is the primary mechanism of melting at mid-ocean ridges?
A. Flux melting
B. Heat transfer melting
C. Volatile addition
D. Decompression melting
Answer: D
, Conceptual Explanation: As tectonic plates pull apart, the underlying mantle rises and
melts due to a decrease in pressure, known as decompression melting.
5. Which factor most significantly increases the viscosity of magma?
A. Increasing silica content
B. Increasing temperature
C. Decreasing crystal content
D. Increasing water content
Answer: A
Conceptual Explanation: Silica (SiO2) forms complex tetrahedral chains that increase
internal friction, thereby increasing viscosity.
6. Which type of volcano is primarily composed of low-viscosity basaltic lava flows?
A. Stratovolcano
B. Shield Volcano
C. Lava Dome
D. Cinder Cone
Answer: B
Conceptual Explanation: Shield volcanoes, like those in Hawaii, are built from fluid
basaltic lava that spreads over long distances.
AND VOLCANISM QUESTIONS AND
ANSWERS 2026/2027 UPDATE || 100%
GUARANTEED PASS
1. Which mineral is the first to crystallize in the discontinuous branch of Bowen’s Reaction
Series?
A. Quartz
B. Biotite
C. Olivine
D. Pyroxene
Answer: C
Conceptual Explanation: Olivine is the first mineral to crystallize at the highest
temperatures in the discontinuous series.
2. What texture is characterized by two distinct sizes of crystals, indicating two stages of
cooling?
A. Aphanitic
B. Phaneritic
C. Porphyritic
,D. Glassy
Answer: C
Conceptual Explanation: Porphyritic texture indicates a period of slow cooling followed
by rapid cooling, creating large phenocrysts in a fine-grained groundmass.
3. Which igneous rock has a felsic composition and a phaneritic texture?
A. Granite
B. Rhyolite
C. Basalt
D. Gabbro
Answer: A
Conceptual Explanation: Granite is a coarse-grained (phaneritic) intrusive rock with a
high silica (felsic) content.
4. What is the primary mechanism of melting at mid-ocean ridges?
A. Flux melting
B. Heat transfer melting
C. Volatile addition
D. Decompression melting
Answer: D
, Conceptual Explanation: As tectonic plates pull apart, the underlying mantle rises and
melts due to a decrease in pressure, known as decompression melting.
5. Which factor most significantly increases the viscosity of magma?
A. Increasing silica content
B. Increasing temperature
C. Decreasing crystal content
D. Increasing water content
Answer: A
Conceptual Explanation: Silica (SiO2) forms complex tetrahedral chains that increase
internal friction, thereby increasing viscosity.
6. Which type of volcano is primarily composed of low-viscosity basaltic lava flows?
A. Stratovolcano
B. Shield Volcano
C. Lava Dome
D. Cinder Cone
Answer: B
Conceptual Explanation: Shield volcanoes, like those in Hawaii, are built from fluid
basaltic lava that spreads over long distances.
