topic 5 ( types of metamorphic rocks )

• Types of Metamorphic Rocks

  • Foliated

  1. slate
  2. phyllite
  3. Metaconglomerate 
  4. Schist
  5. gneiss
  6. Migmatite
• Types of Metamorphic Rocks

  • Non-foliated

  1. Hornfels
  2. Quartzite
  3. marble
• Slate

  • Very fine grained
  • Protolith: shale, mudstone, or rocks composed of clay
  • Low pressure and temperature
• Phyllite


  • Medium to coarse grain
  • Has schistosity
  • Higher temperature than schist
• Schist

  • Foliation due to preferred orientation of very fine grained white mica
  • Slate + enough temperature = neocrystallization 🡪 white mica
• Gneiss

  • Compositionally layered rock
  • Alternating dark and light colored minerals
• Metaconglomerate

  • Protolith: conglomerate
  • Slate or phyllite conditions
  • Produced from flattened clasts
  • Alignment of inequant clasts
• Migmatite

  • Mixture of igneous rock and relict of metamorphic rock
  • Gneiss + melting conditions = felsic magma
  • Felsic magma freezes before flowing out of source area
• Hornfels

  • Variety of metamorphic minerals
  • Mineral assemblage depends on 
  • Protolith composition
  • Temperature and pressure of metamorphism
• Quartzite

  • From pure quartz sandstone metamorphism
  • Quartz 🡪 metamorphism 🡪 recrystallize 🡪 new, larger quartz
• Marble

  • From limestone metamorphism
  • Calcite 🡪 metamorphism 🡪 recrystallize 🡪 new, larger calcite
• Serpentinite

  • Hydrothermal alteration of ultrabasic rocks at <500oC
  • Olivines and Pyroxenes are hydrated into Serpentine minerals
• Soapstone

  • Fine-grained rocks from the alteration of ultrabasic rocks or Mg-rich sedimentary rocks by Low P-T hydrothermal fluids
  • Has talc, magnesite, serpentine, and/or tremolite
  • Soapy feel
• Greenstone

  • Green-colored rocks rich in silicates chlorite, epidote, prehnite, pumpellyite, talc, serpentine, actinolite, albite
  • Low to Moderate alteration of basic and ultrabasic rocks, commonly in oceanic crust near divergent boundaries.
  • Occur in Greenstone Belts abundant in Precambrian
• Amphibolite ( non foliated )

  • Dark-colored rocks composed largely of Amphiboles, garnet and plagioclase
  • Medium to High-T (>550oC) regional metamorphism of basic igneous rocks, calcareous mudrocks and greywackes.
• Granulite ( non )

  • Medium- to coarse-grained with granoblastic to foliated texture
  • Form by high P-T (>800oC, >10kbar, 33km deep) 
  • Dehydration of mafic minerals into pyroxene, k-feldspar, kyanite, garnet; prevents melting
• Eclogite

  • Very high-P, high-T rocks from basalt or gabbro protoliths
  • Stable at 400oC and >1.2GPa at >40km depth; may be the major rock type in lower crust
  • Red by Pyrope garnet, green by Omphacite or Jadeite