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Metamorphic Rock
Rocks formed via heat and pressure, which change the minerals within the rock.
Geothermal Gradient
The average change in temperature that is experienced as material moves into the Earth.
Average Geothermal Gradient
1 Degree Fahrenheit per 100 feet.
Lithostatic Pressure
The pressure that the weight of the rock above a point exerts on a body of rock or sediment.
Volatiles
Components of magma which are dissolved until it reaches the surface, where they expand, including water and carbon dioxide.
Metamorphism
Rocks and minerals that change within the Earth due to heat and pressure.
Regional Metamorphism
Metamorphism that occurs with large-scale tectonic processes, such as collision zones.
Contact Metamorphism
Metamorphism that occurs when rocks are next to a hot intrusion of magma.
Schist
Rock more metamorphosed than phyllite, with visible mica grains and larger porphyroblasts.
Gneiss
A very high grade metamorphic rock with a separation of light and dark minerals.
Quartzite
A metamorphosed sandstone.
Marble
A metamorphosed limestone.
Protolith
The original rocks that existed before metamorphism.
Recrystallization
The process of changing a mineral without melting.
Mineral Rotation and Alignment
A process called foliation that occurs when minerals in rocks realign in response to pressure and heat.
Foliated Texture
A pervasive layering caused by compositional layering or the parallel orientation of platy or elongate mineral grains.
Nonfoliated Texture
A metamorphic rock texture that lacks banding or foliation, appearing granular or crystalline.
Heat (as a metamorphic process)
Increased temperature can cause existing minerals to recrystallize and form new minerals stable at higher temperatures.
Pressure (as a metamorphic process)
Compressive forces can cause minerals to align and create a foliated texture or can compact the rock further.
Chemically Active Fluids and Gasses
Hot, mineral-rich fluids can facilitate chemical reactions within the rock, altering its composition.
Regional Metamorphism Occurrence
Occurs on a large scale in mountain ranges where colliding tectonic plates fold and deform rocks.
Contact Metamorphism Occurrence
Occurs on a small scale when magma or lava heats and transforms the surrounding rock.
Foliated Protoliths
Gneiss has granite as protolith, Schist has shale as protolith.
Non-Foliated Protoliths
Marble has limestone as protolith, Quartzite has sandstone as protolith.
