GLG 103 Lab 1: Skills Review | Questions
and Answers | 2026/2027 Updated | 100%
Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This lab skills review exam assesses foundational competencies in introductory geology laboratory methods,
including scientific reasoning, mineral and rock identification, plate tectonics, geologic time, topographic and
geologic map interpretation, cross-section construction, and structural analysis. Questions emphasize
application, multi-step reasoning, and synthesis across lab skills aligned with NGSS Earth and Space
Sciences and AGI introductory geology guidelines.
STUDY GUIDE
Recommended duration: 2 hours 30 minutes. Passing target: 70%.
HIGHP - Page 1 of 18
,1. A rock sample effervesces vigorously in dilute HCl only after being powdered. Its
hardness is 3, and it exhibits perfect rhombohedral cleavage. Which mineral is most likely
present?
[ ] A. Quartz
[ ] B. Calcite
[ ] C. Halite
[ ] D. Gypsum
CORRECT: B. Calcite
Calcite (CaCO3) reacts with dilute HCl, and powdered calcite effervesces vigorously; its hardness is 3 and it
has perfect rhombohedral cleavage. Quartz does not effervesce and lacks cleavage; halite has cubic
cleavage and a salty taste; gypsum is softer (H=2) and does not effervesce.
2. A topographic map shows a hill with a summit elevation of 1,450 ft. The innermost
closed contour is 1,450 ft, and the next closed contour outward is 1,400 ft. If the contour
interval is 50 ft, what is the highest possible elevation of the hill?
[ ] A. 1,450 ft
[ ] B. 1,475 ft
[ ] C. 1,499 ft
[ ] D. 1,500 ft
CORRECT: C. 1,499 ft
The innermost contour is 1,450 ft, and the next is 1,400 ft, so the hill rises above 1,450 ft but must be less
than 1,500 ft (the next contour interval). The highest possible elevation is just below 1,500 ft, typically
expressed as 1,499 ft or <1,500 ft. Options A and B are too low; D equals the next contour and is not
possible without a 1,500-ft contour.
3. A sequence of sedimentary layers is cut by a dike that does not extend into the
overlying horizontal basalt flow. Which principle is most directly used to determine that
the dike is older than the basalt?
[ ] A. Principle of original horizontality
[ ] B. Principle of cross-cutting relationships
[ ] C. Principle of superposition
[ ] D. Principle of faunal succession
CORRECT: B. Principle of cross-cutting relationships
The principle of cross-cutting relationships states that a geologic feature that cuts another is younger than the
feature it cuts. The dike cuts older layers but is truncated by the basalt, so the dike is older than the basalt.
Superposition applies to layered rocks; original horizontality and faunal succession are not used for
cross-cutting timing.
HIGHP - Page 2 of 18
, 4. A rock sample is fine-grained, dark-colored, and contains abundant olivine and
pyroxene with minor plagioclase. It has aphanitic texture and no visible quartz. This rock
is best classified as:
[ ] A. Granite
[ ] B. Basalt
[ ] C. Rhyolite
[ ] D. Gabbro
CORRECT: B. Basalt
Basalt is aphanitic, dark-colored, mafic volcanic rock composed mainly of pyroxene, plagioclase, and often
olivine. Granite and rhyolite are felsic and contain quartz; gabbro is coarse-grained (phaneritic) and
equivalent in composition to basalt but not aphanitic.
5. On a geologic map, a unit of sandstone is bounded by a fault on one side and an
unconformity on the other. The fault cuts a dike that intrudes the sandstone. Which
statement about relative timing is correct?
[ ] A. The dike is older than the fault.
[ ] B. The fault is older than the sandstone.
[ ] C. The unconformity is younger than the fault.
[ ] D. The dike is younger than the unconformity.
CORRECT: A. The dike is older than the fault.
The fault cuts the dike, so the dike must be older than the fault (cross-cutting relationships). The sandstone
must be older than the fault because the fault cuts it. The unconformity's age relative to the fault is not
specified; only the dike-fault relationship is clearly determined.
6. A mineral sample has a metallic luster, black streak, and is attracted to a magnet. It is
relatively soft (H=5.5-6.5). Which mineral is most likely?
[ ] A. Pyrite
[ ] B. Magnetite
[ ] C. Hematite
[ ] D. Galena
CORRECT: B. Magnetite
Magnetite is metallic, black, magnetic, and has a black streak; its hardness is 5.5-6.5. Pyrite is harder (6-6.5),
has a greenish-black streak, and is not strongly magnetic; hematite has a red-brown streak and is weakly
magnetic at best; galena has a gray streak, perfect cubic cleavage, and is not magnetic.
HIGHP - Page 3 of 18
and Answers | 2026/2027 Updated | 100%
Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This lab skills review exam assesses foundational competencies in introductory geology laboratory methods,
including scientific reasoning, mineral and rock identification, plate tectonics, geologic time, topographic and
geologic map interpretation, cross-section construction, and structural analysis. Questions emphasize
application, multi-step reasoning, and synthesis across lab skills aligned with NGSS Earth and Space
Sciences and AGI introductory geology guidelines.
STUDY GUIDE
Recommended duration: 2 hours 30 minutes. Passing target: 70%.
HIGHP - Page 1 of 18
,1. A rock sample effervesces vigorously in dilute HCl only after being powdered. Its
hardness is 3, and it exhibits perfect rhombohedral cleavage. Which mineral is most likely
present?
[ ] A. Quartz
[ ] B. Calcite
[ ] C. Halite
[ ] D. Gypsum
CORRECT: B. Calcite
Calcite (CaCO3) reacts with dilute HCl, and powdered calcite effervesces vigorously; its hardness is 3 and it
has perfect rhombohedral cleavage. Quartz does not effervesce and lacks cleavage; halite has cubic
cleavage and a salty taste; gypsum is softer (H=2) and does not effervesce.
2. A topographic map shows a hill with a summit elevation of 1,450 ft. The innermost
closed contour is 1,450 ft, and the next closed contour outward is 1,400 ft. If the contour
interval is 50 ft, what is the highest possible elevation of the hill?
[ ] A. 1,450 ft
[ ] B. 1,475 ft
[ ] C. 1,499 ft
[ ] D. 1,500 ft
CORRECT: C. 1,499 ft
The innermost contour is 1,450 ft, and the next is 1,400 ft, so the hill rises above 1,450 ft but must be less
than 1,500 ft (the next contour interval). The highest possible elevation is just below 1,500 ft, typically
expressed as 1,499 ft or <1,500 ft. Options A and B are too low; D equals the next contour and is not
possible without a 1,500-ft contour.
3. A sequence of sedimentary layers is cut by a dike that does not extend into the
overlying horizontal basalt flow. Which principle is most directly used to determine that
the dike is older than the basalt?
[ ] A. Principle of original horizontality
[ ] B. Principle of cross-cutting relationships
[ ] C. Principle of superposition
[ ] D. Principle of faunal succession
CORRECT: B. Principle of cross-cutting relationships
The principle of cross-cutting relationships states that a geologic feature that cuts another is younger than the
feature it cuts. The dike cuts older layers but is truncated by the basalt, so the dike is older than the basalt.
Superposition applies to layered rocks; original horizontality and faunal succession are not used for
cross-cutting timing.
HIGHP - Page 2 of 18
, 4. A rock sample is fine-grained, dark-colored, and contains abundant olivine and
pyroxene with minor plagioclase. It has aphanitic texture and no visible quartz. This rock
is best classified as:
[ ] A. Granite
[ ] B. Basalt
[ ] C. Rhyolite
[ ] D. Gabbro
CORRECT: B. Basalt
Basalt is aphanitic, dark-colored, mafic volcanic rock composed mainly of pyroxene, plagioclase, and often
olivine. Granite and rhyolite are felsic and contain quartz; gabbro is coarse-grained (phaneritic) and
equivalent in composition to basalt but not aphanitic.
5. On a geologic map, a unit of sandstone is bounded by a fault on one side and an
unconformity on the other. The fault cuts a dike that intrudes the sandstone. Which
statement about relative timing is correct?
[ ] A. The dike is older than the fault.
[ ] B. The fault is older than the sandstone.
[ ] C. The unconformity is younger than the fault.
[ ] D. The dike is younger than the unconformity.
CORRECT: A. The dike is older than the fault.
The fault cuts the dike, so the dike must be older than the fault (cross-cutting relationships). The sandstone
must be older than the fault because the fault cuts it. The unconformity's age relative to the fault is not
specified; only the dike-fault relationship is clearly determined.
6. A mineral sample has a metallic luster, black streak, and is attracted to a magnet. It is
relatively soft (H=5.5-6.5). Which mineral is most likely?
[ ] A. Pyrite
[ ] B. Magnetite
[ ] C. Hematite
[ ] D. Galena
CORRECT: B. Magnetite
Magnetite is metallic, black, magnetic, and has a black streak; its hardness is 5.5-6.5. Pyrite is harder (6-6.5),
has a greenish-black streak, and is not strongly magnetic; hematite has a red-brown streak and is weakly
magnetic at best; galena has a gray streak, perfect cubic cleavage, and is not magnetic.
HIGHP - Page 3 of 18
