Chapter 3 – section 4
Sedimentary Rock
Chapter 3 – Section 4
Sedimentary Rocks
What is a sedimentary rock?
Formed from sediments
Sediments – loose
materials such as rock
fragments, mineral
grains, and bits of
shell that have been
moved by wind, water,
ice, or gravity.
Chapter 3 – Section 4
Sedimentary Rocks
Sedimentary rocks are formed from
sediments
Sediments come from already
existing rocks that have weathered
and eroded.
Sedimentary rocks form
when these sediments are
pressed and cemented
together, OR when minerals
form from a solution.
Sedimentary rocks form when these
sediments are pressed and cemented
together, OR when minerals form from a
solution.
See figure 11 on pg. 71
Sedimentary rocks often form in
layers with the oldest layers on the
bottom because they were deposited
first.
Sometimes, forces within Earth
overturn layers of rock, and the
oldest are no longer on the bottom.
Sediments – loose materials such as
rock fragments, mineral grains, and bits
of shell that have been moved by wind,
water, ice, or gravity.
Classifying Sedimentary Rocks
Sedimentary rocks are classified by what
they are made of and how they are
formed.
There are three types – detrital,
chemical, and organic sedimentary rocks
Sedimentary Rocks are
classified into three
types
Detrital
Chemical
Organic
See table 2 on pg. 73.
Detrital Sedimentary Rocks – made from
broken fragments of rocks
Loose sediments are compacted and
cemented together to form a new rock
When rocks are exposed to water, ice, or
air, they break down and weather and
erode. The rocks on this table are classified
by size.
Detrital - made from broken fragments
of rocks
When rocks are exposed to water, ice,
or air, they break down and weather
and erode
(see pg. 72, figure 12)
As rocks erode, they are deposited to
new locations where layer after layer of
sediments build up. Eventually,
pressure from the top layers pushes
down on lower layers. If the sediments
are small, they can stick together and
form solid rock
Compaction – when sediments are
small and compact together to form
solid rock.
Compaction – when sediments are small and
compact together to form solid rock.
(see pg. 73, figure 13).
If sediments are large, they need more
than just pressure to help them stick
together. They have to be cemented
together. Water and dissolved materials
move through open spaces between
sediments and act as a natural cement,
which glues the larger particles together to
make a new rock
Cementation – when water and other
minerals move between the open spaces
of sediments, gluing them together.
See pg. 73,
. table 2.
Shape and size of sediments is also
important. Rocks are named according
to the shape and size of their
sediments.
Cementation – when water and other
minerals move between the open spaces of
sediments, gluing them together.
Chemical Sedimentary Rocks – form
when dissolved minerals come out of a
solution
When saltwater evaporates in a pan,
you can see the salt that is left caked
on the sides and bottom of the pan.
The deposit of minerals that come out
of a solution (from evaporation) form
sediments and rocks.
Chemical Rocks - form when dissolved
minerals come out of a solution
Chemical sedimentary rocks are not
made from existing rocks pieces.
They are made when a solution
evaporates and the mineral is left.
Example – Calcium carbonate is
carried in ocean water. When calcium
carbonate comes out of that solution,
limestone forms.
Limestone is usually deposited on the
bottoms of lakes or shallow seas.
Here’s a short clip about the
sedimentary rock limestone!
Example – Calcium carbonate is carried in
ocean water. When calcium carbonate
comes out of that solution, limestone forms.
Another example of chemical
sedimentary rock is when water that is
rich in dissolved salt evaporates, it
often deposits the mineral halite. Table
salt is made from rock salt.
Organic Sedimentary Rocks – rocks made
out of the remains of once living things.
Example – Fossil rich limestone (different
than chemical rich limestone). This
limestone is formed from the shells of
ocean animals. When shelled animals die,
their shells accumulate on the ocean floor.
When these shells are cemented together,
fossil rich limestone forms.
Organic Sedimentary Rocks – rocks
made out of the remains of once living
things.
Chalk is a soft, white, porous sedimentary rock,
a form of limestone composed of the
mineral calcite.
Chalk cliffs in Dover, United Kingdom
Example – chalk is an organic sedimentary
rock made from microscopic shells.
Examples – fossil rich limestone, chalk,
coal
Example – coal forms when pieces of
dead plants are buried under other
sediments in swamps. These
sediments are compacted over
millions of years to form coal, an
important source of energy.
Here’s a short video
Here’s the end of our song!