52 Questions
During which type of metamorphism does chemical alteration occur from hot, ion-rich water?
Hydrothermal metamorphism
What type of metamorphism occurs during mountain building?
Regional metamorphism
What type of metamorphism results from decreasing temperature and/or pressure, leading to the development of lower temperature/pressure mineral assemblages?
Retrograde metamorphism
Which type of metamorphism progresses incrementally from low-grade to high-grade?
Prograde metamorphism
What are index minerals?
Minerals that are good indicators of the metamorphic conditions in which they form
Which type of metamorphic rocks frequently display compositional banding or layering?
Coarse-grained rocks
What is the basis for the degree of metamorphism referred to as 'metamorphic grade'?
The grain size of the rock
What are rocks with large metamorphic crystals set in a finer grained matrix called?
Porphyroblastic rocks
What is the idea of metamorphic facies based on?
The mineral assemblages coexisting in equilibrium over a range of metamorphic conditions
How are individual metamorphic facies defined in classification schemes?
By specifying the diagnostic mineral assemblage for rocks of common bulk compositions
What are metamorphic facies given names after?
Names of common metamorphic rock types stable under appropriate conditions
What are the two most important factors in defining metamorphic facies?
Temperature and pressure
What is the basic rock type that forms blueschist facies?
Basalt
What gives blueschist its blue color?
The presence of sodium-rich amphibole, glaucophane
What is the typical mineral assemblage of eclogite?
Pyrope garnet and omphacite
What conditions are suitable for forming blueschist facies?
High pressure and low temperature
Which type of metamorphic texture is defined by alignment of platy or inequant minerals in medium-grained rocks?
Schistosity
What type of metamorphic rock texture lacks foliation and develops in minimal deformation environments?
Marble
Which type of metamorphic texture includes large crystals in a fine-grained matrix, such as garnet or staurolite?
Porphyroblastic textures
What is defined by the parallelism or alignment of linear elements in the rock?
Lineation
Which type of metamorphic texture is characterized by highly strained rock layers with elongated grains?
Mylonite layering
What type of metamorphic rock texture has a random orientation of fine-grained rocks?
Hornfelsic textures
Which type of metamorphic texture is defined by compositional layering of equant and platy minerals in coarse-grained rocks?
Gneissosity
What type of metamorphic rock texture contains numerous inclusions in a porphyroblast?
Poikiloblastic textures
Which type of metamorphic texture includes relics of porphyritic volcanic texture in metamorphic rocks?
Blastoporphyritic textures
What type of metamorphic rock texture is defined by the formation of new mineral grains around a rim?
Corona or reaction rim textures
Which type of metamorphic rock lacks foliation and has a mosaic of anhedral grains?
Hornfels
Which of the following is an example of a common metamorphic rock with distinct characteristics and origins?
Quartzite
What is the most important agent of metamorphism?
Heat
What are the two sources of heat for metamorphism?
Heat from magma and increase in temperature with depth
What type of pressure applies forces equally in all directions?
Confining pressure
What are the main components of chemically active fluids in metamorphism?
Mainly water with other volatile components
What is the original, unmetamorphosed rock from which a given metamorphic rock is formed called?
Protolith
Which type of metamorphism takes place at considerable depths over an extensive area?
Regional metamorphism
What type of metamorphism occurs due to a rise in temperature when magma invades a host rock?
Contact or thermal metamorphism
What type of metamorphism is associated with very thick sedimentary strata?
Burial metamorphism
What is the chemical alteration at high temperatures and moderate pressures by hot, ion-rich fluids called?
Hydrothermal metamorphism
What occurs when high speed projectiles called meteorites strike Earth’s surface?
Impact metamorphism
What refers to the size, shape, and arrangement of grains within a rock?
Texture
What does foliation in metamorphic rocks refer to?
Any planar arrangement of mineral grains or structural features within a rock
What is the most important agent of metamorphism?
Heat
What are the sources of chemically active fluids in metamorphism?
Water from magmatic bodies
What is the original, unmetamorphosed rock called?
Protolith
Which type of metamorphism occurs due to a rise in temperature when magma invades a host rock?
Contact or thermal metamorphism
What type of metamorphism takes place at considerable depths over an extensive area under high pressure?
Regional metamorphism
What type of metamorphism is associated with very thick sedimentary strata?
Burial metamorphism
What is the term for the size, shape, and arrangement of grains within a rock?
Texture
What type of metamorphic texture results in parallel alignment of platy and/or elongated minerals?
Foliated texture
What is the most common type of metamorphism along fault zones?
Regional metamorphism
What type of metamorphism occurs when high-speed projectiles called meteorites strike Earth's surface?
Impact metamorphism
What is the term for the parallelism or alignment of linear elements in the rock?
Foliation
What type of metamorphism progresses incrementally from low-grade to high-grade?
Regional metamorphism
Study Notes
Metamorphic Textures and Rock Types Summary
- Foliation can form through rotation, recrystallization, changing shapes of grains, and directed pressure
- Gneissosity is defined by compositional layering of equant and platy minerals in coarse-grained rocks
- Schistosity is defined by alignment of platy or inequant minerals in medium-grained rocks
- Cleavage includes slaty and crenulation cleavage, creating planar surfaces for rock splitting
- Mylonite layering is defined by highly strained rock layers with elongated grains
- Lineation refers to the parallelism or alignment of linear elements in the rock
- Nonfoliated metamorphic rocks lack foliation and develop in minimal deformation environments
- Hornfelsic textures have random orientation of fine-grained rocks, while granoblastic textures form a mosaic of anhedral grains
- Porphyroblastic textures include large crystals in a fine-grained matrix, such as garnet or staurolite
- Blastoporphyritic textures are relics of porphyritic volcanic texture in metamorphic rocks
- Poikiloblastic textures contain numerous inclusions in a porphyroblast, while corona or reaction rim textures form new mineral grains around a rim
- Common metamorphic rocks include slate, phyllite, schist, gneiss, marble, and quartzite with distinct characteristics and origins
Agents and Types of Metamorphism
- Retrograde metamorphic conditions are difficult to attain without the addition of volatiles from an external source due to previous prograde metamorphism depleting the rock in volatile components.
- Heat is the most important agent of metamorphism, driving chemical reactions and recrystallization of minerals with two sources: contact metamorphism and an increase in temperature with depth due to the geothermal gradient.
- Pressure increases with depth and can be either confining (equal stress in all directions) or differential (unequal pressure in different directions).
- Chemically active fluids, mainly water with other volatile components, aid in recrystallization of existing minerals and have sources including water trapped in pore spaces, water released during dehydration of minerals, and water from magmatic bodies.
- The original, unmetamorphosed rock from which a given metamorphic rock is formed is called a "protolith," and most metamorphic rocks have the same overall chemical composition as the parent rock from which they formed.
- Types of metamorphism include contact or thermal metamorphism, hydrothermal metamorphism, regional metamorphism, burial metamorphism, metamorphism along fault zones, and impact metamorphism.
- Contact or thermal metamorphism occurs due to a rise in temperature when magma invades a host rock, forming an alteration zone called an aureole, and produces non-foliated, fine-grained metamorphic rocks.
- Hydrothermal metamorphism results in chemical alteration at high temperatures and moderate pressures by hot, ion-rich fluids, common in basaltic rocks, and can form rich ore deposits.
- Regional metamorphism takes place at considerable depths over an extensive area under high pressure, associated with the process of mountain building and producing the greatest quantity of metamorphic rock.
- Other types of metamorphism include burial metamorphism, which is associated with very thick sedimentary strata, and impact metamorphism, which occurs when high-speed projectiles called meteorites strike Earth's surface.
- Texture refers to the size, shape, and arrangement of grains within a rock, and examples of foliation include parallel alignment of platy and/or elongated minerals, compositional banding, and slaty cleavage where rocks can be easily split into thin, tabular sheets.
Test your knowledge of metamorphic textures and rock types with this quiz. Explore the formation of foliation, gneissosity, schistosity, cleavage, mylonite layering, lineation, and various nonfoliated textures. Identify common metamorphic rocks and their unique characteristics.
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