ESS 101 B EXAMINATION 2 ACTUAL EXAM 2026/2027 |
Complete Solution with Questions and Answers and Detailed
Rationales | Geology Comprehensive Assessment | Pass
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DOMAIN 1: METAMORPHIC ROCKS AND PROCESSES (12 Questions)
Q1: Metamorphic Grade Identification
A metamorphic rock contains garnet, staurolite, and kyanite but lacks sillimanite. What
metamorphic grade and facies does this represent?
A. Low grade, greenschist facies
B. Medium grade, amphibolite facies
C. Medium to high grade, upper amphibolite facies transitioning to granulite [CORRECT]
D. Very low grade, zeolite facies
Correct Answer: C
Rationale: The mineral assemblage garnet + staurolite + kyanite is diagnostic of the
kyanite zone in the upper amphibolite facies. Kyanite (Al₂SiO₅) is the high-pressure
polymorph of aluminum silicate, stable at approximately 500-700°C and 6-12 kbar
pressure. The absence of sillimanite indicates temperatures have not yet reached the
granulite facies conditions where sillimanite replaces kyanite. This Barrovian sequence
(chlorite → biotite → garnet → staurolite → kyanite → sillimanite) represents
progressive regional metamorphism of pelitic (shale) protoliths.
Distractor Analysis:
, ● A is incorrect; greenschist facies contains chlorite, epidote, actinolite—not garnet
or kyanite.
● B is partially correct but underspecified; garnet-staurolite-kyanite assemblage is
specifically upper amphibolite, not general amphibolite.
● D is incorrect; zeolite facies is diagenetic to very low grade with zeolites and clay
minerals.
Q2: Foliation Development
Which metamorphic rock typically exhibits strong foliation due to the preferred
orientation of micas under directed pressure?
A. Quartzite
B. Amphibolite
C. Schist [CORRECT]
D. Hornfels
Correct Answer: C
Rationale: Schist is characterized by strong foliation (schistosity) created by the
preferred orientation of platy minerals, particularly micas (biotite, muscovite) and/or
chlorite. The term "schist" derives from the Greek for "to split," referring to this excellent
rock cleavage. Under directed stress (σ₁ > σ₂ = σ₃), platy minerals rotate and recrystallize
perpendicular to the maximum compressive stress, creating foliation. Quartzite (A) is
typically massive or shows weak foliation; amphibolite (B) may show weak to moderate
foliation from aligned amphiboles; hornfels (D) is typically massive (equidimensional
grains) due to contact metamorphism under confining pressure.
Distractor Analysis:
, ● A is incorrect; quartzite lacks platy minerals and is massive or shows
granoblastic texture.
● B is incorrect; while amphibolite can show foliation, it's defined by amphibole
composition, not foliation intensity.
● D is incorrect; hornfels forms by contact metamorphism with minimal directed
stress, resulting in hornfelsic (granoblastic, equidimensional) texture.
Q3: Protolith Identification
A metamorphic rock consists primarily of calcite with minor dolomite, shows
granoblastic texture, and reacts vigorously with dilute HCl. The protolith was most likely:
A. Shale
B. Basalt
C. Limestone [CORRECT]
D. Granite
Correct Answer: C
Rationale: The mineralogy (calcite ± dolomite), reaction with HCl (diagnostic for
carbonate minerals), and granoblastic texture (interlocking equidimensional crystals)
indicate marble, which forms from the metamorphism of limestone (calcite) or
dolostone (dolomite). This is a monomineralic metamorphic rock where
recrystallization increases grain size but composition remains essentially CaCO₃. Index
minerals in associated rocks might indicate grade, but pure marble shows limited
mineralogical change with grade—only crystal size increases.
Distractor Analysis:
● A (shale) would produce pelitic metamorphic rocks (slate, phyllite, schist, gneiss)
with quartz, micas, garnet, etc.
, ● B (basalt) would produce mafic metamorphic rocks (greenschist, amphibolite,
eclogite) with amphiboles, pyroxenes, plagioclase.
● D (granite) would produce felsic gneiss or migmatite with quartz, feldspars,
micas.
Q4: Index Mineral Significance
Why are index minerals like garnet, staurolite, and sillimanite valuable for determining
metamorphic grade?
A. They are the most common minerals in all metamorphic rocks
B. They have narrow stability ranges in P-T space, making them sensitive indicators of
specific metamorphic conditions [CORRECT]
C. They are always visible to the naked eye
D. They are the only minerals that form during metamorphism
Correct Answer: B
Rationale: Index minerals are diagnostic because they have well-defined, narrow
stability fields in pressure-temperature (P-T) space, making them sensitive
geothermobarometers. For example: (1) Chlorite is stable <~400°C, (2) Biotite appears
~400-450°C, (3) Garnet appears ~500°C (depending on composition), (4) Staurolite
~550-650°C, (5) Kyanite ~500-700°C at moderate pressure, (6) Sillimanite >~650°C.
Their first appearance (isograd) in a metamorphic sequence allows geologists to map
metamorphic zones and infer P-T paths. This is the foundation of metamorphic facies
concept and Barrovian/ Buchan zonation.
Distractor Analysis:
Complete Solution with Questions and Answers and Detailed
Rationales | Geology Comprehensive Assessment | Pass
Guaranteed - A+ Graded
DOMAIN 1: METAMORPHIC ROCKS AND PROCESSES (12 Questions)
Q1: Metamorphic Grade Identification
A metamorphic rock contains garnet, staurolite, and kyanite but lacks sillimanite. What
metamorphic grade and facies does this represent?
A. Low grade, greenschist facies
B. Medium grade, amphibolite facies
C. Medium to high grade, upper amphibolite facies transitioning to granulite [CORRECT]
D. Very low grade, zeolite facies
Correct Answer: C
Rationale: The mineral assemblage garnet + staurolite + kyanite is diagnostic of the
kyanite zone in the upper amphibolite facies. Kyanite (Al₂SiO₅) is the high-pressure
polymorph of aluminum silicate, stable at approximately 500-700°C and 6-12 kbar
pressure. The absence of sillimanite indicates temperatures have not yet reached the
granulite facies conditions where sillimanite replaces kyanite. This Barrovian sequence
(chlorite → biotite → garnet → staurolite → kyanite → sillimanite) represents
progressive regional metamorphism of pelitic (shale) protoliths.
Distractor Analysis:
, ● A is incorrect; greenschist facies contains chlorite, epidote, actinolite—not garnet
or kyanite.
● B is partially correct but underspecified; garnet-staurolite-kyanite assemblage is
specifically upper amphibolite, not general amphibolite.
● D is incorrect; zeolite facies is diagenetic to very low grade with zeolites and clay
minerals.
Q2: Foliation Development
Which metamorphic rock typically exhibits strong foliation due to the preferred
orientation of micas under directed pressure?
A. Quartzite
B. Amphibolite
C. Schist [CORRECT]
D. Hornfels
Correct Answer: C
Rationale: Schist is characterized by strong foliation (schistosity) created by the
preferred orientation of platy minerals, particularly micas (biotite, muscovite) and/or
chlorite. The term "schist" derives from the Greek for "to split," referring to this excellent
rock cleavage. Under directed stress (σ₁ > σ₂ = σ₃), platy minerals rotate and recrystallize
perpendicular to the maximum compressive stress, creating foliation. Quartzite (A) is
typically massive or shows weak foliation; amphibolite (B) may show weak to moderate
foliation from aligned amphiboles; hornfels (D) is typically massive (equidimensional
grains) due to contact metamorphism under confining pressure.
Distractor Analysis:
, ● A is incorrect; quartzite lacks platy minerals and is massive or shows
granoblastic texture.
● B is incorrect; while amphibolite can show foliation, it's defined by amphibole
composition, not foliation intensity.
● D is incorrect; hornfels forms by contact metamorphism with minimal directed
stress, resulting in hornfelsic (granoblastic, equidimensional) texture.
Q3: Protolith Identification
A metamorphic rock consists primarily of calcite with minor dolomite, shows
granoblastic texture, and reacts vigorously with dilute HCl. The protolith was most likely:
A. Shale
B. Basalt
C. Limestone [CORRECT]
D. Granite
Correct Answer: C
Rationale: The mineralogy (calcite ± dolomite), reaction with HCl (diagnostic for
carbonate minerals), and granoblastic texture (interlocking equidimensional crystals)
indicate marble, which forms from the metamorphism of limestone (calcite) or
dolostone (dolomite). This is a monomineralic metamorphic rock where
recrystallization increases grain size but composition remains essentially CaCO₃. Index
minerals in associated rocks might indicate grade, but pure marble shows limited
mineralogical change with grade—only crystal size increases.
Distractor Analysis:
● A (shale) would produce pelitic metamorphic rocks (slate, phyllite, schist, gneiss)
with quartz, micas, garnet, etc.
, ● B (basalt) would produce mafic metamorphic rocks (greenschist, amphibolite,
eclogite) with amphiboles, pyroxenes, plagioclase.
● D (granite) would produce felsic gneiss or migmatite with quartz, feldspars,
micas.
Q4: Index Mineral Significance
Why are index minerals like garnet, staurolite, and sillimanite valuable for determining
metamorphic grade?
A. They are the most common minerals in all metamorphic rocks
B. They have narrow stability ranges in P-T space, making them sensitive indicators of
specific metamorphic conditions [CORRECT]
C. They are always visible to the naked eye
D. They are the only minerals that form during metamorphism
Correct Answer: B
Rationale: Index minerals are diagnostic because they have well-defined, narrow
stability fields in pressure-temperature (P-T) space, making them sensitive
geothermobarometers. For example: (1) Chlorite is stable <~400°C, (2) Biotite appears
~400-450°C, (3) Garnet appears ~500°C (depending on composition), (4) Staurolite
~550-650°C, (5) Kyanite ~500-700°C at moderate pressure, (6) Sillimanite >~650°C.
Their first appearance (isograd) in a metamorphic sequence allows geologists to map
metamorphic zones and infer P-T paths. This is the foundation of metamorphic facies
concept and Barrovian/ Buchan zonation.
Distractor Analysis:
