Chapter 2: Rocks: Section 4: Metamorphic Rock
Origins of Metamorphic Rock
Metamorphic- The word metamorphic
comes from meta, meanind “changed”
and morphos, meaning “shape.”
Metamorphic rocks are those in which
the structure, texture, or composition of
the rock has changed.
It can change by heat or pressure acting
alone or combination of the two.
All rocks can change into Metamorphic
rocks.
A rock can change if the surroundings it is
in changes. If the temperature or
pressure is different from the one the
rock was formed in the rock will underog
metomprphism.
Metamorphic change is caused by
increased pressure at depths greater than
2km.
The temperature at which
metamorphism occurs ranges from 50C
to 1,000C. Temperatures higher than
1000C most rocks will melt.
Metamorphism does not melt rock-when
rock melts, it becomes magma and then
igneous rock.
Composition of Metamorphic Rock
Contact Metamorphism: a rock can
undergo metamorphism by coming
into contact with magma. Magma
will heat surrounding rocks and
“cook” them. As a result the magma
changes some of the minerals in the
surrounding rock into other
minerals.
Regional Metamorphism- When
enormous pressure builds up in rock
that is deeply buried under other
rock formations or when large
pieces of the Earth’s crust collide
with each other.
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Composition of Metamorphic
Rock
When conditions in the Earth’s crust
change because of collisions
between the continents or the
intrusion of magma, the
temperature and pressure of the
existing rock changes.
Minerals that were present in the
rock become unstable in this new
environment and change into
minerals that are more stable in the
new temperature and pressure
conditions.
Some minerals only occur in
metamorphic rock. These minerals
only form within a specific range of
temperature and pressure
conditions.
Scientist can use this information to
estimate the pressure and
temperature that this rock
underwent.
Texture of Metamorphic Rock
Foliated metamorphic rock consists
of minerals that are aligned and
look almost like pages of a book.
Contain mineral grains that are
aligned by pressure.
-Contain flat minerals like biotite
mica.
As these rocks are exposed to heat
and pressure they become other
metamorphic rocks.
Nonfoliated Metamorphic Rocklacks aligned mineral grains. They
are commonly made of only one, or
just a few minerals.
Sandstone is a sedimentary rock
made of quartz sand grains. When
heat and pressure is added and
metamorphism happens the space
between the sand grains disappears
and they recrystallize, forming
quartzite.
Limestone turns to marble