metamorphic rocks

• Aluminium polymorphs:

  • Three aluminium polymorphs 
  • All have the same formula but have different structures 
  • Formed by metamorphism of clay minerals due to different temperatures and pressures 
• Polymorphs:

  • Andalusite 
  • Kyanite 
  • Sillimanite 
• Metamorphic facies:

  • Includes all rocks that have suffered under broadly similar temperatures and pressures 
• Tectonic settings of facies:

  • Facies will be found in the same part of the boundary 
• Retrograde metamorphism:

  • As rocks return to surface pressure and temperatures 
  • Carbonation, hydration, and oxidation occur and new stable minerals are made - retrograde metamorphism 
• Aureole factors:

  • Volume of intrusion 
  • Type of magma 
  • Type of country rock 
  • Dip of intrusion