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. 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.

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

4. 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.

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

6. Regional Metamorphism Regional Metamorphism• •
Most common form of metamorphism
Most common form of metamorphism • •
caused by large scale forces
caused by large scale forces - -
lithospheric plate collision
lithospheric plate collision
covers very large areas • •
covers very large areas - -
metamorphic belts or zones
metamorphic belts or zones - -
Zones are characterized by
Zones are characterized by
Index Minerals
Index Minerals
>
>
form under specific temperatures and pressures
form under specific temperatures and pressures
>
>
metamorphic facies
metamorphic facies
commonly associated with • •
commonly associated with - -
shields: stable areas of crystalline rocks

7. Shields of the World
Shields of the World

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

9. Foliated Texture
Foliated Texture

10. Foliated Textures Foliated Textures • Slatey Slatey • • Schistose- -
looks like blackboard
looks like blackboard - -
distinct bands of minerals
>
>
dull surface
dull surface - -
visible grains
visible mineral grains - -
smooth, thin layering
smooth, thin layering
>
>
garnets, staurolites
garnets, staurolites - -
breaks into flat slabs
breaks into flat slabs - -
may have shiny
may have shiny
>
>
referred to as slatey cleavage
referred to as slatey cleavage
appearance - -
no mineral grains visible
no mineral grains visible
>
>
due to mica minerals
due to mica minerals • •
Phyllitic
Phyllitic • •
Gneissic
Gneissic - -
looks like waxed surface
looks like waxed surface - -
larger grains
larger grains
>
>
has a "sheen" to it
has a "sheen" to it - -
may look like igneous rock
may look like igneous rock - -
may have little "waves" on
may have little "waves" on - -
may have crude banding
may have crude banding
surface
surface
>
>
intensely distorted
intensely distorted
>
>
referred to as
referred to as
crenulations
crenulations - -
different minerals than
different minerals than - -
some small grains visible
some small grains visible
schistose
schistose

11. 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
Phyllite
FOLIATED
Schist
BAND-
ING
Gneiss

12. 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

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

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

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

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

17. 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
Regional
(Heat
&
Pressure)
NONFOLIATED
Limestone or
Dolostone
Marble
Metaconglomerate

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

19. Minnesota Metamorphic Rocks
Morton Gneiss
Some of the oldest rocks in the world include the gneiss found in the Minnesota River Valley.
Morton Gneiss is 3.6 billion years old, is a coarsely crystalline, foliated
Large crystals = rock cooled slowly beneath the Earth’s surface.
Foliation = great heat and pressure

20. Minnesota Metamorphic Rocks
Sediments, fine-grained sand and mud, were deformed by the same forces that caused the uplift of mountains in northern Minnesota.
Schist formed from sediments, uplift, heat and pressure.
Schist is composed predominantly of mica minerals, which impart a platy or layered texture to the rock.
Schist is common in central Minnesota and across northern Minnesota.
Mica Schist

21. Minnesota Metamorphic Rocks
Stream deposits of reddish quartz sand grains were consolidated and slightly altered = quartzite.
The reddish to purple Sioux Quartzite is found at Blue Mound State Park and the Jeffers Petroglyphs in southwestern Minnesota.
At the Pipestone National Monument, the soft, red pipestone the Indians favored for carving is a thin claystone layer between thick layers of quartzite.
Quartzite

22. Minnesota Metamorphic Rocks