Rocks
Sedimentary, Igneous, and
Metamorphic
3 Types of
Sedimentary Rocks
• Clastic
• Chemical
• Organic
Clastic Sedimentary Rock
• Sediments form when rocks are
weathered and eroded
• Sediments are moved by wind,
glaciers and water
• Most clastic sediments are
deposited in the ocean
Clastic Sedimentary Rock
• Sediments are converted into
solid sedimentary rock by
the processes of compaction
and cementation.
Clastic Sedimentary Rock
Compaction & Cementation
Clastic Sedimentary Rock
Compaction & Cementation
Clastic Sedimentary Rock
• Compaction occurs when the weight
of overlying materials compresses
the deeper sediments.
• Cementation occurs when soluble
cementing materials, such as
calcite, silica, and iron oxide,
are precipitated onto sediment
grains, fill open spaces, and
join the particles.
Clastic Sedimentary Rock
• Particle (clast) size is key
to type of rock
– Gravel is > 2 mm
– Sand is 1/16 mm to 2 mm
– Mud is < 1/16 mm
• Clay is < 4 um
• Silt is > 4 um
Sandstone
Conglomerate
Shale
Chemical Sedimentary Rock
• Chemical sedimentary rocks are
made of mineral crystals that
formed from chemicals dissolved
in water.
• The water in the oceans, lakes,
and underground is often full
of dissolved minerals and other
elements.
Chemical Sedimentary Rock
• When water is so full of elements
that not all will fit, some are not
able to remain dissolved.
• They come out of solution, or
precipitate, forming solid mineral
crystals.
• Precipitation is the opposite of
dissolving.
Chemical Sedimentary Rock
• Minerals precipitate when some water
has been evaporated or when a
chemical reaction occurs.
• Evaporation takes only water
molecules into the atmosphere so the
elements in the remaining liquid
water become very concentrated.
Eventually, they do not all fit and
some precipitate out as mineral.
Chemical Sedimentary Rock
Halite
Gypsum
Limestone
Dolomite
Organic Sedimentary Rock
Coal
Bituminous
Anthracite
– Coal: Bituminous & Anthracite
Organic Sedimentary Rock
Coal
• Coal is an organic sedimentary rock
that has been altered slightly by
being compressed and heated.
• It was formed by the rapid burial
of large numbers of plants; swamp
forest.
• Over time the plant material is
compacted so much by the weight of
the overlying sediment that it is
turned in to rock.
Igneous Rocks
Magma is the molten rock material below
the surface.
•Lower density causes magma to rise toward the
surface (compared to the surrounding rock).
• Magma at the surface is lava.
• Igneous rocks are formed from
solidified/cooled magma or lava.
• Igneous rocks are made of interlocking
crystals
Igneous Rock
Igneous Rocks
Magma extruded
onto the Earth’s
surface forms
volcanic or
extrusive
igneous rocks.
Magma that
crystallizes
within the
Earth’s crust
forms plutonic
or intrusive
igneous rock.
Extrusive & Intrusive
Igneous Rocks
• Intrusive- Magma under the
surface
– Coarse-grained (igneous rock)
– Magma cools slowly and large
crystals grow over a long period
of time
– Gabbro, diorite, granite
Extrusive & Intrusive
Igneous Rocks
• Extrusive- Lava at the surface
– Fine-grained (igneous rock)
– Lava cools very quickly,
consequently crystals do not have
time to grow and develop
– Basalt, andesite, rhyolite,
obsidian
Igneous Rocks
Molten rock or
magma(1,000-1,200
contains chemical
elements.
oC),
If the magma begins to
cool, elements begin to
form chemical bonds
within the magma and
crystals start to
develop.
Igneous Rocks
Rocks that form from magma or lava cooled from
high temperatures tend to contain a lot of
iron and magnesium but little silica.
These rocks are called mafic and tend to be
dominated by dark colored minerals such as
amphibole and pyroxene (Elements: iron &
magnesium).
Igneous Rocks
When magma cools slowly, minerals that form at
cooler temperatures dominate the resulting
rock.
These rocks are called felsic and tend to be
light colored with minerals such as feldspar
and quartz. (Elements: silicon, oxygen,
sodium, potassium, & aluminum)
Igneous Rocks
Igneous Rocks
Igneous Rocks
Classification of Igneous Rocks
-Texture: crystal size
-Color
-Mineral composition
Igneous Rocks
Granite
•Felsic
•Intrusive
Igneous Rocks
Rhyolite
•Felsic
•Extrusive
Igneous Rocks
Basalt
•Mafic
•Extrusive
Igneous Rocks
Gabbro
•Mafic
•Intrusive
Igneous Rocks
Andesite
•Intermediate
•Extrusive
Igneous Rocks
Diorite
•Intermediate
•Intrusive
Igneous Rocks
Other Igneous Rocks
• Lava flows
• Fragmented magma ejected
explosively
– Ash plumes
– Pyroclastic flows
• Cool and solidify very quickly;
no minerals develop
Consequently they cannot be
mafic, intermediate, or felsic
Igneous Rocks
Obsidian
•Extrusive
Igneous Rocks
Pumice
•Extrusive
Metamorphic Rocks
Metamorphic Rocks
The Greek word meta means “change” and morph meaning
“shape”.
Metamorphic rocks were previously either sedimentary or
igneous rocks, but they have been subjected to very high
temperature and pressure. (Below the surface of the
Earth)
Metamorphic Rocks
The temperature was not high enough to make the rock melt
(Metamorphic changes occur as the rock is in solid-state),
but it was high enough to allow some crystals to grow, and
for the minerals to begin to re-crystallize and thus form a
new rock.
As temperature rises, crystal
lattices are broken down and
reformed with different
combinations of atoms. New
minerals are formed.
Metamorphic Rocks
The types of metamorphism
Regional metamorphism
Contact metamorphism
Contact metamorphism
Regional metamorphism
Metamorphic Rocks
Contact metamorphism
In the case of contact metamorphism heat comes from
contact with molten magma.
-This type of metamorphism has a limited and local effect.
Metamorphic Rocks
Regional metamorphism
When rocks are forced toward the mantle
during the formation of a mountain range
and/or other tectonic activity, regional
metamorphism occurs.
-Large volumes of rock are altered in this
way.
Metamorphic Rocks
Metamorphism does not take place on the Earth’s surface.
Rocks under the Earth’s surface are under great pressure
from overlying rock layers.
Deep burial- as depth increases, in the Earth’s crust, the
temperature also increases.
Tectonic forces in the Earth may apply lateral pressure to
large volumes of rock.
Metamorphic Rocks
Metamorphic Rocks
Metamorphic Rocks
Metamorphic rocks have been
exposed to the surface of the
Earth because erosion has
striped away overlying rocks.
So, when we see a large area of
metamorphic rocks we know we are
looking at the core of an
ancient mountain range.
Changes During Metamorphism
Parent rock
(protolith)
Low temperature
Low pressure
shale
slate
High temperature
Medium temperature
Higher temp.
High pressure
Medium pressure
Higher pressure
phyllite
quartz
sandstone
limestone
basalt
granite
schist
gneiss
quartzite
marble
MELTING
amphibolite or schist
gneiss
Metamorphic Rocks
Change in metamorphic grade with depth
Increasing Directed Pressure and increasing Temps
Metamorphic Rocks
Foliated metamorphic rock
Foliation forms when pressure squeezes the flat or
elongate minerals within a rock so they become aligned.
These rocks develop a platy or sheet-like structure that
reflects the direction that pressure was applied in.
Foliation: minerals have been rearranged into visible
bands.
Metamorphic Rocks
Increasing Directed Pressure and increasing Temps
Metamorphic Rocks
Directed Pressure causes rocks to become folded, and minerals to reorient
perpendicular to the stress: “foliation”
Schist
Gneiss
Slate
Metamorphic Rocks
Non-foliated metamorphic rock
Non-foliated metamorphic rocks do not have a platy or
sheet-like structure.
Metamorphic rock that does not show bands.
Marble
Quartzite