Metamorphic Rocks
Chapter 3.4
Metamorphic Rocks
• The word metamorphic means to “change form”.
• Metamorphic rocks are formed when one type of
rock changes or transforms into another by the
extreme pressures and temperatures that can be
produced on the earth.
• Under ordinary circumstances, the only place
you can find these extreme temperatures and
pressures is deep within the earth’s crust.
Two Types of Metamorphism
• There are two main types of metamorphism.
• Contact Metamorphism occurs when magma
comes into close contact with a rock and doesn’t
melt it, but cooks it. This causes a
recrystallization of the rock to occur.
• Regional Metamorphism occurs when large
regions such as mountain ranges and tectonic
plates move, causing extreme pressures and
temperatures to recrystallize the rocks.
Contact vs. Regional Metamorphism
Contact Metamorphism –
Cooking, but not melting
Regional Metamorphism –
Cooking, pushing, bending, and
twisting all at the same time.
Classification of Metamorphic Rocks
• The two different agents of metamorphism both
cause two very different textures for
metamorphic rocks.
• Foliated Metamorphic Rocks are formed by
Regional Metamorphism (Pressure).
• Foliation gives a layered or banded appearance.
• Nonfoliated Metamorphic Rocks are
formed by Contact Metamorphism (Heat).
• Nonfoliated Metamorphic Rocks often have a
coarse crystalline texture.
Foliated Metamorphic Rocks created
by Regional Metamorphism
Slate is a Foliated
Metamorphic Rock
with a dull
appearance
Phyllite is similar to
Slate but notice the
wavy or glossy sheen
Schist has many varieties
but one of the more
common types seen here
has many layers of
muscovite mica present
More Foliated Metamorphic Rocks
Gneiss (pronounced nice) has a
banded or tiger-striped
appearance
Another type of Schist,
called Garnet Schist
has small Garnet
Gemstones in it.
Progression of Metamorphic Rocks
• Metamorphic Rocks can transform into different metamorphic
rocks depending on the conditions. Slate for example can change
into Phyllite, Phyllite into Schist, and Schist in Gneiss.
Nonfoliated Metamorphic Rocks
created by Contact Metamorphism
Quartzite, created by
Quartz Sandstone
that got “cooked”
Marble, created by
Limestone that got
“cooked”
Anthracite Coal is
similar to Bituminous
Coal, but notice how
shiny it is. This is what
happened to Bituminous
Coal that gets “cooked”
Metamorphic Rock Classification
A Parent Rock is the name of a rock that metamorphic
rock originated from. A good example is limestone, which
is the Parent Rock of Marble.