1. Metamorphic Rocks

2. All metamorphic rocks were originally igneous or sedimentary.
Metaconglomerate
Conglomerate
All metamorphic rocks were originally igneous or sedimentary.
Heat and pressure over long periods of time alter the original rock
The pressure may be from the top
Or sides

3. The metamorphic process may cause any of the
following to occur to the rock:
1. An overall increase in the rock density
2. The appearance of new mineral crystals (ex. diamond, garnet
graphite, or talc)
3. An alignment of existing crystals or new crystals to
produce a certain foliation
4. A recrystallization of existing minerals (ex. calcite
crystals in the limestone become altered to
form marble)

4. This often produces slate from shale
Low grade metamorphism results from the weight
of overlying sediments plus some heat from below
This often produces slate from shale

5. (low grade)
Pressure from
weight of overlying
sediment

6. To produce high level metamorphism, much
more pressure is needed than can be provided
by the weight of overlying sediments
This pressure comes from the side from
plate collision
After sideways squeezing

7. This sideways squeezing
produces metamorphic
rocks like schist

8. Schist rock resulting from high lateral squeezing

9. Another schist rock

10. garnet schist

11. If the intense squeezing is combined with extremely high temperatures, a gneiss is produced.
This is the highest degree of metamorphism a rock can undergo without melting

12. banded gneiss

13. Garnet gneiss

14. hornblende
gneiss

15. All of the metamorphism you have seen so
far has been regional metamorphism
In regional metamorphism the entire region is subject
to pressure and or high temperature
When hot molten rock (magma) comes up to the surface from deep inside the earth, the high temperature of the magma alters the rock which comes in contact with it.
This is known as contact metamorphism

16. Hornfels
magma

17. Contact metamorphism here

22. How can you tell if a rock is METAMORPHIC?
Look for Banding or Foliation of Mineral Crystals (NOT layering of sediment grains)
Look for evidence of deformation, like intense folding
Look for new mineral crystals forming in the rock (garnet)