1. Chapter 4 - Rocks
Identifying rocks and their place in the
rock cycle.
Section 2: Igneous Rocks
2. Igneous Rocks
The Latin prefix “igni”
means fire, so Igneous
Rocks are born of “fire”.
When magma or lava
cools, minerals begin to
crystallize.
When different minerals
form interlocking
crystals, a rock is
formed.
These crystals make up
the mineral grains of a
rock.
3. Magma Composition
The type of rock formed
often depends on what
minerals are in the
magma/lava.
Some magma/lava has a
lot of Silica (Silicon and
Oxygen compound,
Quartz)
Magma/lava that has a lot
of silica in it will produce
light colored rocks like
granite.
Magma/lava that has little
silica in it will produce dark
colored rocks like basalt.
4. Intrusive Igneous Rocks
Sometimes the mineral grains are large and
sometimes they are small.
If the grains are large, the minerals that
make up the rock must have had a longer
time to form-this is because the magma
cooled slowly underground.
These rocks are called Intrusive Igneous
Rocks.
They are said to be coarse grained.
Example, Granite!
5. Intrusive Igneous Rocks
Due to its ability to
hold up against
weathering and
erosion, Granite is
used as a building
material and for
tombstones.
7. Extrusive Igneous Rocks
If the grains are really
really small, the
minerals that make up
the rock must have
formed from quickly
cooling LAVA. Rocks
exposed to the
atmosphere cool very
fast.
These rocks are called
Extrusive Igneous Rocks
are said to be fine
grained.
“Fast is Fine”
8. Very Fast Cooling Extrusive
Igneous Rocks
This is called a
“volcanic glass” or
obsidian. It has no
mineral grains
because it cooled
soooo fast!
Also, sometimes
extrusive rocks
have holes in
them. These are
from trapped gas
bubbles…A sign of
very fast cooling.
Ex. Pumice
14. Sedimentary Rocks
95% of the crust is
made of Igneous
Rocks, but 75% of the
visible rocks at the
surface are
Sedimentary Rocks.
Sediments can include
rock fragments,
mineral grains, bits of
plant / animal remains
and even minerals
dissolved in water!
Sedimentary Rocks
form mainly in layers.
16. Steps to the formation of a Sedimentary Rock…
3. Deposition- Particles
“Settle Out” of water or
1. Weathering- sometimes wind. Often
Water and wind this means the particles
break up rocks at will fall to the bottom of a
Earth’s surface 2. lake or ocean.
4.
5.
17. Sedimentary Rocks Form in Layers
-Law of Superposition -oldest rock layers will be on
the bottom
-Sedimentary rock layers often give clues to Earth’s
past environments.
-Exs. Fossils and ripple marks
18. Classifying Sedimentary Rocks
Sedimentary Rocks
are classified by how
they form ( &
sometimes what they
are made from).
1. Chemical-some
rocks form from
evaporation.
2. Organic- some from
dead organisms.
3. Clastic- some from
other rock or mineral
pieces.
We will look at the seven common Sedimentary
Rocks!
19. Clastic Sedimentary Rocks
Clastic rocks form
from bits and
pieces of other
older rocks that are
smashed together!
Conglomerate is an
example of a
clastic rock.
20. Clastic Sedimentary Rocks
Sandstone is made of
sand grains.
Shale is mainly made of
small pieces of clay.
Shale is very common
here and can be in many
different shades!
Look at the
layers in the
shale…
21. Where did Shaler get it’s name?
Contrary to popular belief, Shaler is
not named for its many shale
deposits. Shaler was named in honor
of a Pittsburgh judge, Charles Shaler
in 1847.
23. Chemical Sedimentary Rocks
Chemical rocks form
when minerals
dissolved in a solution
evaporate.
Limestone and Rock
Salt are examples of
chemical sedimentary
rocks.
24. Chemical Sedimentary Rocks
Water in the ocean contains
dissolved calcite (a mineral
and compound of calcium,
carbon and oxygen –
CaCO3). When water
evaporates, calcite forms
crystals. This is the main
mineral in limestone.
Limestone is used in cement
and is also part of the
smelting process in
steelmaking.
25. Chemical Sedimentary Rocks
Much of the
bedrock in the
United States is
made of
limestone which
indicates that
large portions of
the country
were once under
water in shallow
oceans.
Generalized geographic map of the United
States 300 mya.
26. Chemical Sedimentary Rocks
Rock Salt is used
to melt snow and
ice.
Rock Salt
contains the
mineral halite,
plus traces of
other materials.
Recall that halite
forms when
seawater
evaporates.
27. Organic Sedimentary Rocks
Organic rocks form from the
remains of once living
things.
Coquina (Fossil Limestone)
is formed from shells
pressed and cemented
together.
Sea organisms make shells
mainly from calcite (CaCO3
they extract the ingredients
from the ocean).
Although Fossil Limestone
and chemical limestone are
both made mainly of calcite,
they formed differently.
28. Organic Sedimentary Rocks
Larger mussels, coral
and snail shells cement
together to produce
Coquina, but tiny shells
combine to produce
Chalk, another form of
organic fossil limestone.
The White Cliffs of
Dover in England are
entirely made of tiny
dead animals!
30. Organic Sedimentary Rocks
Coral Reefs are created
as small animals create
skeletons around
themselves from
dissolved calcite, die,
and leave behind their
skeletons which more
Coral build upon. A coral
reef is another form of
organic fossil limestone!
They are found on the
warm, shallow edges of
oceans and are
important habitats for
many sea animals.
Ancient Coral Reef!
31. Organic Sedimentary Rocks
Coal formed from plant
remains buried in low
oxygen swampy areas
for millions of years.
It is the primary fossil
fuel source for
producing electricity in
the United States.
It is also the primary
cause for air pollution
and possibly Global
Warming!
35. Metamorphic Rocks
The word
metamorphic means
change.
Intense heat and
pressure can change
any rock into a
metamorphic rock.
The intense heat and
pressure for
Metamorphism is
caused by things
like…
36. Metamorphism
1. Mountain Building
(Pieces of Earth’s
crust colliding and
uplifting)
2. Contact with hot
Magma
3. Pressure from
overlying rocks
37.
38.
39. Classifying Metamorphic Rocks
Metamorphic Rocks are
classified by the pattern
in their mineral grains.
High temperatures
change the size and
shape of the crystals or
grains in the rock.
Tremendous pressure
may cause the mineral
Flat, Parallel Layers
grains to line up in flat,
parallel layers.
40. Foliated Metamorphic Rocks
This results in the rock
either cleaving into flat
sheets, or a banding of
the minerals in the rock.
Geologists call this
banding texture and/or
flat sheets foliated.
Flat, Parallel
Layers
Flat Sheets
42. Non-Foliated Metamorphic
Rocks
Metamorphic rocks
which have
minerals grains
that are not
banded or layered
are considered to
be non-foliated.
Ex. Marble.
43. Non-Foliated Metamorphic
Rocks
Marble is a non-
foliated rock used for
building materials and
due to it being fairly
soft, for carving
statues and
monuments.
44.
45.
46. Complete the activity on identifying the five
Metamorphic Rocks and their Igneous or
Sedimentary counterparts…
Notas del editor
Ripple Marks indicate water currents such as would be found in rock that formed at the bottom of a stream bed.
1847 – date Shaler was named. Shale is made of pieces of mud and clay. Shale often forms in quiet lakes and swamps.
The salt works by lowering the melting or freezing point of water. When you add salt to water, you introduce dissolved foreign particles into the water. The freezing point of water becomes lower as more particles are added until the point where the salt stops dissolving. When you pour rock salt onto ice, the sodium and chloride ions interfere with the bonds between the water molecules that make up the ice. This makes it easier for the water molecules to break free of the bond and makes it harder for them to refreeze. This shifts the balance so more molecules are melting than freezing, and the ice begins to melt. CaCl2 works better (at lower temperatures) than NaCl because 3 ions will form, not just 2.
These chalk beds were formed around 70 to 100 million years ago, during the “Cretaceous period,” when the southern portion of England was submerged by a shallow tropical sea. Chalk slowly accumulated and the land was eventually uplifted by movements of the earth’s crust to where the cliffs tower over the Strait of Dover up to 350 feet (105 m) high. Although traditionally composed of natural chalk, modern blackboard chalk is generally made from the mineral gypsum ( calcium sulfate ), often supplied in sticks of compressed powder about 4 in (10 cm) long.
Metamorphic Rocks can sometimes look squished!
Contact with hot magma but not enough to melt it….just enough to change it!