METAMORPHIC ROCK
• Metamorphic –
Formed from older
“parent rock” (either
igneous or
sedimentary) under
intense heat and/or
pressure far beneath
the earth’s surface.
Formation of Metamorphic Rock
Meaning to change
shape
Changes with
temperature and
pressure, but remains
solid
Usually takes place
deep in the Earth
Types of Metamorphism
Contact Metamorphism:
occurs when rocks are heated by nearby magma
Regional Metamorphism:
occurs deep in the Earth where pressures build up and are able
to create a chemical change in rocks
Composition of Metamorphic Rocks
• Minerals that were present in the rock when it
formed may not be stable in the new
temperature and pressure conditions.
• Original minerals change into minerals that
are more stable in the new conditions.
Index Minerals
• Many of these minerals ONLY form in
metamorphic rocks. Some of these form only at
certain temperatures and pressures.
• These minerals are known as Index Minerals, and
are used to estimate the temperature, depth, and
pressure at which a rock undergoes
metamorphism.
• Ex of Index Minerals – biotite mica, chlorite,
garnet, kyanite, muscovite mica, sillimanite, and
staurolite.
Textures of Metamorphic Rocks
Foliated- mineral grains are arranged in planes or
bands.
- Results when rocks are subjected to both high
temperatures and high pressures.
- Typically associated with regional metamorphism
gneiss
As shale is
exposed to
more and
more heat
and pressure,
it continually
changes into
different
types of
metamorphic
rock
Textures of Metamorphic Rocks
Nonfoliated- mineral grains are not arranged in
planes or bands
-May result when rocks are subjected to high
temperatures and low pressures
- Typically associated with small scale, contact
metamorphism
Marble
Examples
• Sandstone
• Shale
Quartzite
Slate
Examples
Limestone
Marble
Granite
Gneiss
Metamorphic Rock QUESTIONS
Determine if the following rock samples are
foliated or non-foliated:
Amphibolite
Quartzite
Phyllite
Foliated