GEOLOGY 1001 SOLUTION MANUAL
Course: Introductory Geology
SECOND EXAMINATION — OFFICIAL ANSWER KEY & RATIONALES Total Questions: 50
1. An tabular intrusive igneous body that cuts across pre-existing rock layering (discordant) is a:
Answer: A dike
RATIONALE: Dikes are discordant tabular intrusions that cut across surrounding rock bedding. Sills are parallel
(concordant) to existing layers.
2. Intrusive igneous rocks that cool slowly deep underground typically display which texture?
Answer: B phaneritic
RATIONALE: Slow insulation underground provides ample time for mineral crystals to grow large enough to be visible to
the naked eye (phaneritic texture).
3. According to Bowen’s Reaction Series, which mineral crystallizes first from a cooling silicate melt?
Answer: D olivine
RATIONALE: Olivine crystallizes at the highest temperatures ($\approx 1200^\circ\text{C}$) at the start of the discontinuous
branch of Bowen's Reaction Series.
4. A porphyritic texture in an igneous rock indicates which cooling history?
Answer: C two-stage cooling (slow then fast)
RATIONALE: Large crystals (phenocrysts) form during slow cooling deep underground, followed by rapid eruption and
cooling of the matrix (groundmass) on or near the surface.
5. Decompression melting occurs predominantly at which tectonic environment?
Answer: E a and b (mid-ocean ridges and continental rifts)
RATIONALE: Upwelling mantle rock experiences lower pressure without losing heat, allowing it to cross the solidus and
melt along divergent boundaries and rifts.
6. A volcano composed of alternating layers of pyroclastic debris and intermediate lava flows is a:
Answer: B stratovolcano (composite volcano)
RATIONALE: Stratovolcanoes (e.g., Mt. Fuji, Mt. St. Helens) build steep cones from alternating lava flows, ash fall, and
pyroclastic flows.
7. Broad, gently sloping volcanoes built almost entirely from successive fluid basaltic lava flows are:
Answer: A shield volcanoes
RATIONALE: Low-viscosity basaltic lavas spread over wide areas before solidifying, forming broad, low-profile shield
volcanoes like Mauna Loa.
8. Fast-moving clouds of superheated gas, ash, and rock fragments that race down volcanic slopes are:
Answer: C pyroclastic flows
RATIONALE: Pyroclastic flows (nueés ardentes) are high-density mixtures of gas and tephra that travel downhill at speeds
GEOLOGY 1001 — Second Exam Answer Key Page 1 of 5
, 10. Smooth, ropey basaltic lava surfaces are termed:
Answer: B pahoehoe
RATIONALE: Pahoehoe forms when fluid basalt lava forms a thin skin that wrinkles as the flow continues beneath it.
Blocky, jagged basalt is termed 'a'a.
11. Pillow basalts are characteristic indicators of volcanic eruptions occurring:
Answer: A underwater
RATIONALE: Rapid quenching of molten basalt by water creates rounded, bulbous lobes called pillow structures on the
ocean floor.
12. Mechanical weathering that occurs when water repeatedly freezes and expands in rock fractures is:
Answer: D frost wedging
RATIONALE: Water expands by approximately $9\%$ upon freezing, generating high pressures that split rock fractures
apart over repeated freeze-thaw cycles.
13. Chemical weathering proceeds most rapidly in climates that are:
Answer: C warm and wet
RATIONALE: High temperatures accelerate chemical reaction rates and abundant moisture provides the essential reactant
solvent for hydrolysis and dissolution.
14. Which mineral is most resistant to chemical weathering at Earth’s surface conditions?
Answer: A quartz
RATIONALE: Quartz forms at low temperatures on Bowen's series and features strong, fully polymerized 3D Si-O bonds,
making it chemically stable.
15. The chemical reaction of iron-bearing silicate minerals with atmospheric oxygen to form hematite is:
Answer: B oxidation
RATIONALE: Oxidation involves the loss of electrons (conversion of $\text{Fe}^{2+}$ to $\text{Fe}^{3+}$), forming reddish
iron-oxide minerals like hematite or goethite.
16. Dissolution of limestone landscapes produces unique topography characterized by sinkholes and
caves called:
Answer: D karst topography
RATIONALE: Slightly acidic groundwater dissolves calcite in limestone along joint sets, resulting in sinkholes, subterranean
drainage, and caves.
17. Chemical weathering of potassium feldspar via hydrolysis yields which main residual product?
Answer: C clay minerals
RATIONALE: Hydrolysis breaks down feldspar in the presence of acidic water to form kaolinite (clay minerals) and release
soluble potassium ions.
18. Mechanical weathering increases the efficiency of chemical weathering by:
GEOLOGY 1001 — Second Exam Answer Key Page 2 of 5
Course: Introductory Geology
SECOND EXAMINATION — OFFICIAL ANSWER KEY & RATIONALES Total Questions: 50
1. An tabular intrusive igneous body that cuts across pre-existing rock layering (discordant) is a:
Answer: A dike
RATIONALE: Dikes are discordant tabular intrusions that cut across surrounding rock bedding. Sills are parallel
(concordant) to existing layers.
2. Intrusive igneous rocks that cool slowly deep underground typically display which texture?
Answer: B phaneritic
RATIONALE: Slow insulation underground provides ample time for mineral crystals to grow large enough to be visible to
the naked eye (phaneritic texture).
3. According to Bowen’s Reaction Series, which mineral crystallizes first from a cooling silicate melt?
Answer: D olivine
RATIONALE: Olivine crystallizes at the highest temperatures ($\approx 1200^\circ\text{C}$) at the start of the discontinuous
branch of Bowen's Reaction Series.
4. A porphyritic texture in an igneous rock indicates which cooling history?
Answer: C two-stage cooling (slow then fast)
RATIONALE: Large crystals (phenocrysts) form during slow cooling deep underground, followed by rapid eruption and
cooling of the matrix (groundmass) on or near the surface.
5. Decompression melting occurs predominantly at which tectonic environment?
Answer: E a and b (mid-ocean ridges and continental rifts)
RATIONALE: Upwelling mantle rock experiences lower pressure without losing heat, allowing it to cross the solidus and
melt along divergent boundaries and rifts.
6. A volcano composed of alternating layers of pyroclastic debris and intermediate lava flows is a:
Answer: B stratovolcano (composite volcano)
RATIONALE: Stratovolcanoes (e.g., Mt. Fuji, Mt. St. Helens) build steep cones from alternating lava flows, ash fall, and
pyroclastic flows.
7. Broad, gently sloping volcanoes built almost entirely from successive fluid basaltic lava flows are:
Answer: A shield volcanoes
RATIONALE: Low-viscosity basaltic lavas spread over wide areas before solidifying, forming broad, low-profile shield
volcanoes like Mauna Loa.
8. Fast-moving clouds of superheated gas, ash, and rock fragments that race down volcanic slopes are:
Answer: C pyroclastic flows
RATIONALE: Pyroclastic flows (nueés ardentes) are high-density mixtures of gas and tephra that travel downhill at speeds
GEOLOGY 1001 — Second Exam Answer Key Page 1 of 5
, 10. Smooth, ropey basaltic lava surfaces are termed:
Answer: B pahoehoe
RATIONALE: Pahoehoe forms when fluid basalt lava forms a thin skin that wrinkles as the flow continues beneath it.
Blocky, jagged basalt is termed 'a'a.
11. Pillow basalts are characteristic indicators of volcanic eruptions occurring:
Answer: A underwater
RATIONALE: Rapid quenching of molten basalt by water creates rounded, bulbous lobes called pillow structures on the
ocean floor.
12. Mechanical weathering that occurs when water repeatedly freezes and expands in rock fractures is:
Answer: D frost wedging
RATIONALE: Water expands by approximately $9\%$ upon freezing, generating high pressures that split rock fractures
apart over repeated freeze-thaw cycles.
13. Chemical weathering proceeds most rapidly in climates that are:
Answer: C warm and wet
RATIONALE: High temperatures accelerate chemical reaction rates and abundant moisture provides the essential reactant
solvent for hydrolysis and dissolution.
14. Which mineral is most resistant to chemical weathering at Earth’s surface conditions?
Answer: A quartz
RATIONALE: Quartz forms at low temperatures on Bowen's series and features strong, fully polymerized 3D Si-O bonds,
making it chemically stable.
15. The chemical reaction of iron-bearing silicate minerals with atmospheric oxygen to form hematite is:
Answer: B oxidation
RATIONALE: Oxidation involves the loss of electrons (conversion of $\text{Fe}^{2+}$ to $\text{Fe}^{3+}$), forming reddish
iron-oxide minerals like hematite or goethite.
16. Dissolution of limestone landscapes produces unique topography characterized by sinkholes and
caves called:
Answer: D karst topography
RATIONALE: Slightly acidic groundwater dissolves calcite in limestone along joint sets, resulting in sinkholes, subterranean
drainage, and caves.
17. Chemical weathering of potassium feldspar via hydrolysis yields which main residual product?
Answer: C clay minerals
RATIONALE: Hydrolysis breaks down feldspar in the presence of acidic water to form kaolinite (clay minerals) and release
soluble potassium ions.
18. Mechanical weathering increases the efficiency of chemical weathering by:
GEOLOGY 1001 — Second Exam Answer Key Page 2 of 5
