What are Metamorphic Rocks?

Metamorphic rocks forms due to heat and temperature which changes the original rock or parent rock into new rock. The parent rocks are sedimentary, igneous, or metamorphic. The metamorphic word comes from Greek and means “to change form“.

Metamorphic rocks are forms due to changes through a geological process like tectonic movements and magma intrusions. These geological process changes the mineral composition and texture of the pre-existing igneous and sedimentary rocks to form metamorphic rocks. The process through which existing rocks change into metamorphic rocks is called metamorphism. Metamorphic rocks form 12% of the earth’s surface. The study of metamorphic rocks gives us information about the temperature and pressure that occur at great depth within the earth’s crust.

There are 3 factors that cause an increase in pressure and the formation of metamorphic rock.

  1. Weight of the overlying layer of sediment.
  2. Stress due to plates colliding.
  3. Stress due to plates sliding past each other.

Types of Metamorphism

There are 3 types of metamorphism are contact, regional, and dynamic metamorphism.

  • Contact Metamorphism
  • Regional Metamorphism
  • Dynamic Metamorphism

Contact Metamorphism:

When magma comes in contact with rocks(country rock), the temperature is highest near magma and decreases to distance. the area near the magma alters the rocks, the area surrounding the igneous intrusion is called contact metamorphism.

Regional Metamorphism:

Happened in a greater area. large geological process e.g mountain building produces regional metamorphism. schist and gneiss produce due to metamorphism.

Dynamic Metamorphism:

It also produces by mountain building. rock bend, folded, crushed, and sheared because of heat and pressure. breccias composed of angular shattered rock fragments to very fine-grained, granulated, or powdered rocks with clear foliation and lineation. direct pressure is the main agent of dynamic metamorphism.

Metamorphic Rocks and Their Parent Rocks

There are two types of Metamorphic Rocks

  • Foliated Metamorphic Rocks 
  • Non-Foliated Metamorphic Rocks

Foliated Metamorphic Rocks 

Foliated metamorphic rocks are formed due to direct exposure to pressure and heat. Most important and largest groupings of metamorphic rocks. Foliated metamorphic rocks have four distinguishable types of aligned textures and normally have a banded or layered appearance. Examples are slate, gneiss, phyllite, and schist.

Metamorphic RocksParent RocksMineralogyMetamorphismCrystal Size
SlateShaleClay minerallow-grade Regional MetamorphismVery Fine
PhyliteShaleClay mineral, Muscovite, Biotitelow-grade Regional MetamorphismFine 
SchistShale, BasaltMuscovite, Quartz, Garnet, Biotite, PlagioclaseMedium-grade Regional MetamorphismMedium to Course
GneissBasalt, granite, shaleplagioclase, orthoclase, quartz, biotite, amphibole, pyroxenehigh-grade regional metamorphismMedium to Course
SerpentinitePeridot, duniteserpentine, magnetite, talc, chloriteLow-grade regional metamorphismMedium to Course
Blue schistBasaltBlue amphibole, Green micalow-grade Regional Metamorphism, High pressureFine to Medium
Green schistBasaltGreen Amphibole, Green mica, PlagioclaseMedium-grade Regional MetamorphismFine to Medium
AmphiboliteBasaltAmphibole, Plagioclase, Biotite, QuartzMedium-grade Regional metamorphismMedium to Course

Non-Foliated Metamorphic Rocks

Non-foliated metamorphic rocks are formed due to tectonic movement or direct pressure and Its formation is dependent on existing rocks. These metamorphic rocks don’t have bands or layered appearance. Examples are quartzite, hornfels, and novaculite.

Metamorphic RocksParent RocksMineralogyMetamorphismCrystal Size
QuartziteSandstoneQuartzRegional or Contact MetamorphismFine to course
MarbleLimestoneCalciteRegional or Contact MetamorphismFine to course
HornfelsShalePyroxene, Amphibole, PlagioclaseContact MetamorphismFine 

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