Download Metamorphic Rocks

Entry Task

What questions would you ask in order to
figure out what type of rock this is?
Which rock is intrusive?
Metamorphic Rocks
“ A changed life”
Meta=change Morph=shape

Extreme heat and pressure change the
texture and mineral composition of existing
rocks
Metamorphism
Metamorphism: a change
Metamorphic rocks: changed rocks;
A rock whose texture or composition (or both)
has changed due to increased temperature,
pressure, or interaction with hot fluids
Protolith- what the rock was originally
Metamorphism can result in:
•
Recrystallization of minerals.
•
Crystallization of new minerals from old
ones.
•
Plastic deformation of the rock.
Metamorphic Grade
Metamorphic Grade is the degree to which
a rock has changed from the protolith.
Low grade = low temperature 200 degrees
Celsius (mica formed)
Intermediate grade = 300-800 degrees
Celsius
High grade = 800+ degrees Celsius
Factors Controlling Metamorphism
Temperature, Pressure, Hydrothermal Fluids
Two types of pressure:

Directed Pressure: unequal pressure;
greater from a particular direction

Confining Pressure: general pressure
from all directions.
Types of Metamorphism
Regional
 Contact
 Tectonic

Regional Metamorphism

Change created by rocks being buried
under new rocks.

The old rocks are exposed to heat and
intense pressure.

If the rock melts, it is no longer a
metamorphic rock, it is an igneous rock.
Contact metamorphism

When magma comes in contact with the
surface, the rocks at the surface are
changed and become a metamorphic rock.

How do you think they were changed?
Tectonic metamorphism

Rocks at plate boundaries are changed due
to the heat and pressure of the plates
moving past each other.
Foliation

Coarse-grained minerals separate and line
up in bands.

Example: gneiss (nice)
Metamorphic Rocks
Metamorphic Rocks
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Sandstone ~ quartzite
Limestone ~ marble
Shale ~ slate ~ schist
Calcite, quartz, & hematite ~ garnet schist
Granite ~ gneiss
Schist

A regional, medium grade metamorphic
rock.

What does that definition tells us about its
origin?
Schist
Protolith: Phyllite
Is this a regional or contact
metamorphic rock? Your
evidence?
Slate
Protolith: shale
Graphite
Protolith: bituminous coal