1. METAMORPHIC ROCKS
Rocks that form from other pre-existing rock (sedimentary, igneous, or metamorphic) that have been changed from high temperature and/or high pressure

2. Metamorphic Rocks

3. Conditions that cause rock to undergo metamorphism include:
Heat - Under conditions of high temperature from magma contacting pre-existing rock.
Pressure - Deep burial and pressure from mountain formation.

4. Types of Metamorphism
1. Contact Metamorphism
2. Regional Metamorphism

5. Contact Metamorphism Deep burial and pressure from mountain formation.
The main metamorphic agent is heat.
Also forms when pre-existing rock comes into contact with molten lava or magma. The heat from the molten material is hot enough to cause the minerals in the original rock to re-crystallize, but not melt.

6. Regional Metamorphism
Covers large areas typically associated with mountains
Deep burial and pressure from mountain formation.
Heat and Pressure change the rock

7. Types of Metamorphic Rocks
Foliated: rocks with mineral crystals arranged in cable-like distorted layers/structures
Mineral Alignment
Banding
Nonfoliated: rocks with recrystallized minerals; no layering
Recrystallization: This is the growth of new mineral crystals from other rocks.

8. Scheme for Metamorphic Rock Identification
Texture
Composition
Type of Metamorphism
Comment
Rock Name
Mica
Regional
(Heat and Pressure increase w/ depth)
Low-Grade metamorphism of SHALE
Mica, Quartz, Feldspar, Amphiboles, Garnet
Foliation surfaces shiny from microscopic mica crystals
Mica, Quartz, Feldspar, Amphiboles, Garnet, Pyroxene
Platy mica crystals visible
Compact, may split easily
Slate
ALIGNMENT
MINERAL
FOLIATED
Phyllite
Schist
BAND-
ING
Gneiss

9. Rock Name Rock Type Shale Sedimentary ----- Slate Metamorphic Low
Progression of Metamorphism
Start with a shale and then hit
it with heat and pressure!
Rock Name
Rock Type
Grade of Metamorphism
Shale
Sedimentary
-----
Slate
Metamorphic
Low
Phyllite
Low/Intermediate
Schist
Intermediate/High
Gneiss
High
Molten Rock
Cools into Igneous Rock
More
Heat
&
Pressure

10. Shale
(Sedimentary Rock)
Slate
(Metamorphic Rock)
Heat
&
Pressure

11. Slate
(Metamorphic Rock)
Phyllite
(Metamorphic Rock)
Heat
&
Pressure

12. Phyllite
(Metamorphic Rock)
Heat
&
Pressure
Schist
(Metamorphic Rock)

13. With even more heat & pressure (High-Grade Metamorphism)
… you end up with something
that is really Gneiss! 13

14. Scheme for Metamorphic Rock Identification
Texture
Composition
Type of Metamorphism
Comment
Rock Name
Variable
Contact
(Heat)
Various rocks changed by nearby magma/lava
Quartz
Metamorphism of Quartz
Calcite and/or Dolomite
Metamorphism of
Various minerals in particles and matrix
Pebbles may be distorted or stretched
Hornfels
Sandstone
Quartzite
NONFOLIATED
Regional
(Heat
&
Pressure)
Marble
Limestone or
Dolostone
Metaconglomerate 14

15. Where are metamorphic rocks found?
At the interface between igneous and sedimentary rocks
Mountainous regions

16. How are rocks classified?
THE ROCK CYCLE
How are rocks classified?