Transcript Unit 8-3: The Rock Cycle Part III: Metamorphic

Unit 9-3: The Rock Cycle Part
III:
Metamorphic Rocks
Let’s start by looking at what
metamorphic rocks are:
-Not formed from magmas or
sediments.
-Contain the same minerals as
igneous and sedimentary rocks.
-They are formed from the
action of heat, pressure, and
chemicals acting on igneous
and sedimentary rock.
-Most of the metamorphic
rock in the earth’s crust
formed by dynamic
metamorphism.
-Occurs during mountainbuilding movement.
-Horizontal layers deep in the
earth are subjected to high
temperatures and pressures.
-Additional heat and pressure from rock movement adds to the
regular heat and pressure.
-Gases join with the rock to produce striking changes.
-Also called regional metamorphism because it occurs over large
areas.
-What happens to rocks that are
metamorphosed?
-Pressure squeezes grains
together.
-This makes rocks more dense
and less porous.
-Crystals are realigned.
-Example: Sandstone is changed
into quartzite.
-Denser
-Nonporous
-Highly crystalline
-Limestone changes into marble.
-More dense
-More crystallized form of calcite.
Quartzite
Limestone
Marble
Sandstone
-When shale undergoes
metamorphosis, even more
changes occur.
-More dense
-More crystalline
-Mica and horneblende form
-The new minerals are made into
tiny, needlelike parallel layers.
-These layers break easily.
-This is called foliation.
-Shale can form slate, phyllite, and
schist.
Slate
-Slate is the first rock formed
from the metamorphism of shale.
-The foliation layers are
microscopically thin.
-If metamorphism continues, then
the slate becomes phyllite.
-Phyllite is very shiny in
appearance.
-The third stage is schist.
-The foliation in schist is very
easily seen.
Schist
Phyllite
-Schist:
-Forms from shale mostly
-Can also form from impure
sandstones and basalt.
-Schists are named for their
primary mineral:
-Mica schist
-Talc schist
-Horneblende schist
Granite
-Gneiss:
-Forms from shale, granite,
conglomerate, etc.
-Coarsest foliation out of all
metamorphic rocks.
-Cardboard-thick parallel bands
with alternating light and dark
colored minerals.
Gneiss: Note the
thick, alternating
layers of light and
dark.
-Thermal Metamorphism:
-When magma is near rocks, its heat changes the surrounding
rock.
-Hot liquids and gases can mix with the surrounding solid rock.
-This is a contact-based, so very localized metamorphism.
-Never produces foliation.
-Hornfel is formed through thermal metamorphism.
-Fine-grained, dense, and very hard.
Granite
Hornfel