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Metamorphic Terms
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- 1Metamorphism- Changes in heat and/or pressure that result in solid-state changes in texture, mineralogy, and/or chemical composition (NO MELT)
- Occurs from 250 to ~850 degrees Celsius and ~2-3 kb to < 10 kb - 2Protolithpre-existing (parent) rock
- 3Factors that Determine Metamorphic ProductsHeat and Pressure
- 4Solid state diffusionatoms migrate through the crystal structure and rebond
- 5Recrystallization- change in mineral size/shape with no change in composition
- equal pressure in all directions and heat = recrystallization
- Results in lower porosity and nonfoliated metamorphic rocks - 6Neocrystallizationgrowth of new minerals from the same elements
- 7Phase ChangeThe transformation of a mineral to its polymorph(s) due to changes in crystal structure but not composition
- 8Texturesize and shape of minerals
- 9Mineralogycomposition
- 10Quartzite- Metamorphosed quartz sandstone
- forms from the recrystallization of quartz grains due to the elevated temps and pressures
- Moh's: 7
- nonfoliated - 11Marble- metamorphosed limestone CaCO3
- forms from the recrystallization of limestone due to elevated temps and pressures
- Moh's: 3, preferred for sculpting
- Nonfoliated - 12Foliation- Pressure in unequal directions and heat = foliation
- Compression and shear results in changes in shape and/or parallel realignment of inequant mineral grains and newly formed minerals
- a planar alignment of newly-formed platy or elongate minerals with their long axes at 90 degrees to the greatest pressure direction - 13Metamorphic Grade- the max temp and pressure regime a rock has experienced
- low grade: 250-400degrees C and 2-6 kb
- medium grade: 400-600degrees C and 6-8 kb
- high grade: (>600degrees C and 8-10 kb) - 14LithostaticEqual in all directions/nonfoliated rocks
- 15Differentialunequal/foliated rocks
- Slate, phyllite, schist, gneiss (shale and siltstone are protoliths) - 16Protolith MineralogyAs temp and pressure increase, the protolith's minerals recombine to form new minerals that are stable under the new conditions
- 17PorphyroblastLarge well-shaped minerals in a finer-grained groundmass that have grown as a response to metamorphism
- 18Index mineralsform in a predictable order due to solid state diffusion and indicate the temps and pressures a metamorphic rock formed in
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- (Metamorphic Rocks) Geology Fichas sobre Metamorphic Terms, creado por Arielle Loftis el 27/04/2017.
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- Arielle Loftis
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