1. Stage 3 Revision
Metamorphic Rocks

2. Metamorphic Revision Rock Cycle 3 R’s Types of Metamorphism
Regional
Contact
Dynamic
Metasomatic
Metamorphic Grades
Increasing with Pressure/Temperature

3. Index Minerals
The presence of certain minerals in a Metamorphic rock tells you the temp and the pressure it was formed at
Many of these minerals are only present in Metamorphic rocks
Some of these minerals are Polymorphs
A polymorph is a compound that has differing atomic structures eg Diamond/Graphite

4. Polymorphs Mineral crystallisation occurs under specific conditions.
Diamonds exist under the crust where the pressure and temps are very great, and must be brought up fast (in a volcano) too slow and they will turn into Graphite

5. Al2SiO5 The best index mineral in Metamorphic rocks. Kyanite
Sillimanite
Andalusite

6. These minerals are all made from the same elements/compound Al2SiO5
But they only form at certain temperatures
The presence of any tells you the approximate temp and pressure the rock formed at.

7. Metamorphic Textures Pressure causing alignment of minerals
Sheet like texture called Foliation
Increased grain size
Due to incresed temperatures and pressure for a longer period

8. Texture - Foliation
Here you have minerals growing in a preferred orientation in the rock. Some layers are thin others are thick.
Foliation can give a rock a striped or streaky appearance
Foliated rocks are distinguished by their grain size and nature of the foliation.
Minerals such as Muscovite (Mica) and Chlorite

9. Slate The finest grained foliated rock
Parent rock (Protolith) Shale, Mudstone
LOW grade metamorphism (what does this mean?)
The rock has a slaty CLEAVAGE in one direction. That comes from the pressure above and below the rock.
Minerals:
Chlorite
Clay or Mica (Muscovite)
Quartz*
Feldspar*
* In smaller amounts

10. Phyllite Fine grained Parent rock: Slate
Names after the greek for leaf because the rock has a leafy lustre.
Minerals:
Mica
Chlorite
Feldspar*
Quartz*
* in smaller amounts

11. Schist Medium to Coarse grained rock
Schistocity: Preferred orientation of larger Mica crystals (than Phyllite) caused by stress (from the pressure that would have caused the metamorphism)
Also the formation of wavy or distorted surfaces instead of flat planes
Forms at a higher temp than Phyllite
Minerals:
Kyanite
Feldspar
Quartz
Amphibole
Garnet (Sometimes as a Porphyroblast/clast)

12. Gneiss
Coarse grained
Alternating layers of dark and light coloured minerals
Gneissic texture, high grade metamorphism
Banding, Banding can occur for different reasons
Temperature causing minerals to grow in bands
Sheering helping the minerals grow in bands
Minerals
Quartz
Biotite
Garnet
Feldspar
Sillimanite

13. Other textures Lineation Banding Augen
Minerals grow as prismatic crystals facing a similar direction
Banding
As mentioned previously
Augen
Quartz and similar silica minerals can be squashed into an ellipsoid shape (eye)

14. Other textures Granular Folding This is important!
All mineral grains in a metamorpic rock are approximately the SAME SIZE. Because they have been exposed to the same pressure/temp for the same time. These occur in rocks with a simple chemistry (eg Sandstone SiO2 and Limestone CaCO3)
These are generally NOT foliated but have had high temps!
Folding
Directional pressure can make rocks behave plastic
Now for these types (and the others) what types of metamorphism could they be related to?

15. Non Foliated
Here the crystals have grown without anything restricting their growth (or making them grow in a preferred orientation)
Often formed without any pressure-only temp
The crystals are interlocking
Often made of only one mineral

16. Hornfels Parent rock: Shale, mudstone, limestone Fine grained
Minerals: Dependent on Parent rock (can differ)
Shale or clay hornfels are made of Biotite but have Andalusite and Sillimanite in it.
What does that say about its formation location?

17. Quatrzite Parent rock: Sandstone
Original loose SiO2 grains that have recrystallised making larger and interlocking formation.
Minerals:
SiO2 (Quartz)

18. Marble Parent rock: Limestione
Original loose CaCO3 grains that have recrystallised making larger and interlocking formation.
All fossils destroyed
Mineral:
CaCO3 (Calcium Carbonate or Calcite)

19. Metamorphic Grade
As pressure and/or temperature increases so does the amount of change a metamorphic rock makes. This is the Grade

20. Metamorphic Grade
As the Metamorphic Grade increases the minerals in the rock changes as well.
They change in a predictable pattern depending on Pressure and Temperature.

21. Metamorphic Facies
These are a set of metamorphic mineral assemblages (or ingredients) that relate to a certain range of pressure or temperature

22. Metamorphic Resources
Industrial
Talc
Graphite
Garnet
Asbestos
Kyanite, Andalusite & Sillimanite
Building
Slate
Marble
Quartzite
Gneiss