Petrography is the branch of petrology that focuses on the detailed description, classification, and analysis of rocks through macroscopic and microscopic examination. It involves studying the mineral composition, texture, structure, and fabric of rocks to understand their origin, formation processes, and geological history.
Key techniques in petrography include:
Macroscopic analysis: Visual inspection of hand samples to observe color, grain size, layering, and overall appearance.
Microscopic analysis: Using a petrographic microscope on thin sections (slices of rock about 30 micrometers thick) to identify minerals based on optical properties such as birefringence, pleochroism, and extinction angles.
Advanced methods: Incorporating electron microscopy, X-ray diffraction, and chemical analysis to enhance mineral identification and quantify rock properties.
Petrography applies to various rock types:
Igneous rocks: Examining crystal size, shapes, and arrangements to infer cooling rates and magma composition (e.g., in basalts or granites).
Sedimentary rocks: Analyzing grains, cements, and fossils to determine depositional environments and diagenetic changes (e.g., in sandstones or limestones).
Metamorphic rocks: Assessing foliation, recrystallization, and mineral assemblages to reconstruct metamorphic conditions (e.g., in schists or gneisses).
This field is essential in geology for resource exploration, environmental studies, engineering (e.g., assessing rock stability), and archaeological dating. By integrating petrographic data with other geological sciences, it provides insights into Earth’s crustal evolution and natural processes.
Table of contents
- Part 1: OnlineExamMaker – Generate and share petrography quiz with AI automatically
- Part 2: 20 petrography quiz questions & answers
- Part 3: Save time and energy: generate quiz questions with AI technology
Part 1: OnlineExamMaker – Generate and share petrography quiz with AI automatically
The quickest way to assess the petrography knowledge of candidates is using an AI assessment platform like OnlineExamMaker. With OnlineExamMaker AI Question Generator, you are able to input content—like text, documents, or topics—and then automatically generate questions in various formats (multiple-choice, true/false, short answer). Its AI Exam Grader can automatically grade the exam and generate insightful reports after your candidate submit the assessment.
What you will like:
● Create a question pool through the question bank and specify how many questions you want to be randomly selected among these questions.
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Part 2: 20 petrography quiz questions & answers
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1. Question: What is the primary texture observed in basalt?
A. Phaneritic
B. Aphanitic
C. Porphyritic
D. Vesicular
Answer: B. Aphanitic
Explanation: Basalt is a fine-grained igneous rock that cools quickly, resulting in an aphanitic texture where crystals are too small to be seen with the naked eye.
2. Question: Which mineral is commonly used to identify the protolith in metamorphic rocks?
A. Quartz
B. Garnet
C. Olivine
D. Calcite
Answer: B. Garnet
Explanation: Garnet often forms in metamorphic rocks and can indicate the original rock type based on its composition and association with other minerals.
3. Question: In petrographic analysis, what does the term “cleavage” refer to?
A. The color of a mineral
B. The way a mineral breaks along planes of weakness
C. The crystal shape
D. The hardness of a mineral
Answer: B. The way a mineral breaks along planes of weakness
Explanation: Cleavage is a key optical property in petrography that helps identify minerals by observing how they fracture.
4. Question: Which rock type is characterized by graded bedding in petrographic thin sections?
A. Igneous
B. Sedimentary
C. Metamorphic
D. Volcanic
Answer: B. Sedimentary
Explanation: Graded bedding is a sedimentary structure formed by deposition from turbidity currents, visible in thin sections as varying grain sizes.
5. Question: What optical property is observed when a mineral exhibits double refraction?
A. Birefringence
B. Pleochroism
C. Extinction
D. Twinning
Answer: A. Birefringence
Explanation: Birefringence occurs when light splits into two rays in anisotropic minerals, a common feature examined under a polarizing microscope in petrography.
6. Question: In igneous petrography, what does a glassy texture indicate?
A. Slow cooling
B. Rapid cooling
C. High pressure
D. Low temperature
Answer: B. Rapid cooling
Explanation: A glassy texture, as in obsidian, forms when magma cools too quickly for crystals to develop.
7. Question: Which accessory mineral is often used for radiometric dating in petrographic studies?
A. Zircon
B. Feldspar
C. Mica
D. Pyroxene
Answer: A. Zircon
Explanation: Zircon crystals contain uranium and lead, making them ideal for age determination through methods like U-Pb dating.
8. Question: What is the typical fabric observed in foliated metamorphic rocks?
A. Random grain orientation
B. Layered or banded alignment
C. Spherical structures
D. Porous texture
Answer: B. Layered or banded alignment
Explanation: Foliation in metamorphic rocks results from directed pressure, causing minerals to align in parallel layers.
9. Question: In petrography, how is the term “intergranular” porosity described?
A. Pores between grains
B. Pores within grains
C. Fractures in rocks
D. Voids from dissolution
Answer: A. Pores between grains
Explanation: Intergranular porosity refers to the space between sediment or rock grains, which is crucial for understanding reservoir rocks.
10. Question: Which mineral shows high relief in thin sections due to its high refractive index?
A. Quartz
B. Rutile
C. Muscovite
D. Orthoclase
Answer: B. Rutile
Explanation: Rutile has a high refractive index, causing it to stand out with high relief against other minerals in petrographic analysis.
11. Question: What does the presence of cross-bedding indicate in sedimentary petrography?
A. Wind or water currents
B. Volcanic activity
C. High temperature
D. Chemical precipitation
Answer: A. Wind or water currents
Explanation: Cross-bedding forms from the migration of sediments by currents, providing clues about depositional environments.
12. Question: In petrographic terms, what is “extinction angle” used for?
A. Identifying plagioclase feldspar
B. Measuring mineral hardness
C. Determining rock age
D. Assessing porosity
Answer: A. Identifying plagioclase feldspar
Explanation: Extinction angle in polarized light helps distinguish types of plagioclase based on the angle at which minerals go dark.
13. Question: Which texture is indicative of a plutonic igneous rock?
A. Vesicular
B. Phaneritic
C. Pyroclastic
D. Aphanitic
Answer: B. Phaneritic
Explanation: Phaneritic texture, with visible interlocking crystals, forms in slowly cooling intrusive rocks like granite.
14. Question: What feature is commonly associated with contact metamorphism in petrography?
A. Aureoles
B. Fault lines
C. Sedimentary layers
D. Volcanic flows
Answer: A. Aureoles
Explanation: Contact metamorphism creates metamorphic aureoles, zones of altered rock around igneous intrusions.
15. Question: In thin section analysis, what does a mineral’s interference color indicate?
A. Its birefringence
B. Its density
C. Its chemical composition
D. Its origin
Answer: A. Its birefringence
Explanation: Interference colors in crossed polars result from birefringence, helping to identify minerals like quartz or calcite.
16. Question: Which rock is typically examined for microfossils in petrographic studies?
A. Limestone
B. Granite
C. Basalt
D. Gneiss
Answer: A. Limestone
Explanation: Limestone often contains microfossils, which are preserved organic remains visible in thin sections.
17. Question: What does the term “seriate texture” mean in igneous petrography?
A. Grains of varying sizes
B. Uniform grain size
C. Layered grains
D. Glassy matrix
Answer: A. Grains of varying sizes
Explanation: Seriate texture features a range of crystal sizes, indicating variable cooling rates in igneous rocks.
18. Question: In metamorphic petrography, what is “recrystallization”?
A. Reforming of minerals under heat and pressure
B. Erosion of rock surfaces
C. Addition of new elements
D. Formation of pores
Answer: A. Reforming of minerals under heat and pressure
Explanation: Recrystallization involves the reorganization of mineral grains, leading to new textures in metamorphic rocks.
19. Question: Which optical effect is seen in minerals like tourmaline under the microscope?
A. Pleochroism
B. Fluorescence
C. Luminescence
D. Opalescence
Answer: A. Pleochroism
Explanation: Pleochroism causes color changes in minerals when viewed from different angles in polarized light.
20. Question: What is the significance of twinning in petrographic identification?
A. It helps distinguish minerals like plagioclase
B. It indicates rock age
C. It measures porosity
D. It shows chemical reactions
Answer: A. It helps distinguish minerals like plagioclase
Explanation: Twinning, such as albite twinning, is a crystal structure feature used to identify specific minerals in thin sections.
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Part 3: Save time and energy: generate quiz questions with AI technology
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