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Questions and Answers
Which statement best describes foliation?
Which statement best describes foliation?
- The formation of large crystals
- A process of mineral dissolution
- A random arrangement of minerals
- An alignment of mineral grains perpendicular to the direction of compression (correct)
Under which temperature and pressure conditions could a metamorphic rock containing beta quartz and andalusite have formed?
Under which temperature and pressure conditions could a metamorphic rock containing beta quartz and andalusite have formed?
- 400°C and 0.5 kbar
- 300°C and 2 kbar
- 600°C and 1 kbar (correct)
- 800°C and 3 kbar
Match the steps in neocrystallization with their correct order:
Match the steps in neocrystallization with their correct order:
Protolith minerals are consumed by chemical reactions = 1 Thin clay minerals begin to align = 2 Clay grains flatten out and become parallel to one another = 3 Small garnets appear = 4
What is the result of shear stress in metamorphic rocks?
What is the result of shear stress in metamorphic rocks?
What effects does uniform pressure have on metamorphic rocks?
What effects does uniform pressure have on metamorphic rocks?
Which rock formed as a result of plastic deformation?
Which rock formed as a result of plastic deformation?
What is the best classification for the metamorphic rock shown below?
What is the best classification for the metamorphic rock shown below?
Rank the following mineral assemblages from highest grade to lowest grade: 1.garnet, feldspar, and sillimanite; 2.garnet, staurolite, and muscovite; 3.chlorite, quartz, and biotite; 4.clay and chlorite.
Rank the following mineral assemblages from highest grade to lowest grade: 1.garnet, feldspar, and sillimanite; 2.garnet, staurolite, and muscovite; 3.chlorite, quartz, and biotite; 4.clay and chlorite.
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Study Notes
Foliation
- Defined as the alignment of mineral grains perpendicular to the direction of compression, indicating a structural characteristic of certain metamorphic rocks.
Metamorphic Rock Analysis
- Rocks containing beta quartz and andalusite are formed under specific conditions of approximately 600°C and 1 kbar pressure.
Neocrystallization Steps
- Initial step involves the consumption of protolith minerals through chemical reactions.
- Thin clay minerals start to align in response to stress.
- Clay grains undergo flattening, achieving a parallel orientation to each other.
- Appearance of small garnets marks the later stages of neocrystallization.
Shear Stress Effects
- Results in the elongation of mineral grains.
- Associated with the development of foliation in metamorphic rocks.
Uniform Pressure Effects
- Leads to the formation of large, equant mineral grains.
- Causes the rounding of existing mineral grains in metamorphic rocks.
Plastic Deformation
- Rock C is identified as having formed through the process of plastic deformation, showcasing changes at a microscopic level.
Gneiss Classification
- The depicted metamorphic rock is classified as gneiss, a type known for its banded appearance and mineral composition.
Mineral Assemblage Ranking
- Highest grade assemblage includes garnet, feldspar, and sillimanite.
- Intermediate grades display garnet, staurolite, and muscovite.
- Chlorite, quartz, and biotite represent lower-grade materials.
- The lowest grade consists of clay and chlorite, indicating a progression in metamorphic intensity.
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