Metamorphic Rocks

1
Metamorphic Rocks

• Metamorphic means change in form. Metamorphic
  rocks form from the chemical and physical
  alterations of pre-existing igneous or
  sedimentary rocks. This is done by subjecting
  these rocks to conditions of great heat and
  pressure and chemical activity.

2
Main effects upon rocks

• The heat, pressure and chemical activity will
  effect the metamorphic rocks
• Mineralogy a new mineralogy will form
• Texture the rock texture will alter.

3
Classification of Metamorphic rocks

• There are two classes of metamorphic rocks.
• Contact (thermal) these form when an igneous
  intrusions are injected into the crust. Heat
  from the magma metamorphoses (changes) the
  surrounding rock forming a new metamorphic rock

4

• Regional Metamorphic Rocks these rocks form
  over millions of years and many thousands of
  meters of sediments accumulated in the ocean
  basins. The overlying weight causes the
  sediments to lithify and eventually metamorphose.
• Example shale metamorphoses into slate

5
Agents of Metamorphism

• The agents of change for metamorphic rocks are
• Heat, pressure and chemical activity

6
Identification clue

• These rocks are difficult to identify because
  remember they used to be another kind of rock but
  because of high heat and pressure they look bent,
  twisted, tortured and or cooked. They tend to be
  dense and very hard. They some times show
  banding like when a granite metamorphoses to
  gneiss.

7
Identification clue

• Sometimes the flat minerals like mica all line
  up parallel to each other due to extreme
  pressure. This is called schistosity and the
  rock is called a schist.

8
Identification Clue

• Metamorphic Rocks are
• Fubars
• That is they are
• fouled up beyond all recognition