Metamorphic Rocks
A metamorphic rock is a pre-existing
rock that has changed due to its
exposure to tremendous heat,
pressure and/or mineral fluids.
Formation of
Metamorphic Rocks
Metamorphism – or the process
of making metamorphic rock –
takes place within the
lithosphere.
Contact
Metamorphism –
The metamorphism
of rock that comes
into contact with
igneous intrusions
and/or extrusions.
Regional Metamorphism – The
metamorphism of rock that is associated
with motions of the Earth’s lithosphere.
Contact
Metamorphis
m
Zone of contact metamorphism
Contact Metamorphism will occur in rock
that is adjacent to an igneous intrusion or
extrusion.
The rock that the magma or lava flows
across will be changed due to an increase
in temperature and its reactions with the
liquified minerals in the magma/lava.
A gabbro (igneous) intrusion can be seen above (black-colored rock). The surrounding
gray rock is limestone. A thin layer of marble (white-colored rock) can be found between
the two types of rocks. The marble formed as a result of contact metamorphism.
Regional
Metamorphis
m
Regional Metamorphism
will occur in rock that is
subjected to the intense
heat and pressure
created by movement
within the Earth’s
lithosphere.
The Himalayan Mountains were
created through motions within
the Earth’s lithosphere. These
motions created a great deal of
heat and pressure in the rock
transforming the rock through
regional metamorphism.
Types of
Metamorphic Rocks
Foliated
Metamorphic Rock
Foliated metamorphic rock contains layers of minerals that have
recrystallized due to exposure to high heat and high pressure. Foliated
rocks are associated with regional metamorphism.
These layers of recrystallized minerals can be seen as bands.
Most foliated metamorphic rocks are made up of several minerals.
SLATE: fine-grained crystals
SCHIST: medium-grained crystals
GNEISS: coarse-grained crystals
The more heat and pressure associated with regional metamorphism, the more minerals
will recrystallize and realign into bands within a metamorphic rock.
Types of
Metamorphic Rocks
Nonfoliated
Metamorphic Rock
Nonfoliated metamorphic rocks do not contain layers of minerals.
Minerals within these rocks are interconnected due to exposure to high
heat but not as high pressure. Nonfoliated rocks are associated with
contact and/or regional metamorphism.
Bands are NOT present in nonfoliated metamorphic rock.
Nonfoliated metamorphic rocks can be made up of one mineral or
several minerals.
The high heat and pressure have
caused the pebbles in this
METACONGLOMERATE to
“stretch”.
The QUARTZITE and MARBLE lack bands associated with foliated rocks.
Both metamorphic rocks formed from one mineral (quartz) or a
monomineralic rock (limestone).
Identification of
Metamorphic Rocks
“Which metamorphic rock would
react with hydrochloric acid?”
RT = Pg. 7
MARBLE
“Which foliated, metamorphic
rock is medium grained and
contains platy mica crystals?”
SCHIST