Transcript ES_LV1_Rock_Cycle_files/Unit 9
Unit 9-2: The Rock
Well, I’ve broken out of
wrestling, and now have to
get the the set of another
Scorpion King movie. I’ve
asked a buddy to help out
with the next section.
Well, lets take
at are some nice sediments.
There are three types of sediments:
what makes sedimentary
rock different from igneous -Clastic
rock. Lets start with
rock and mineral
-Examples: plant materials
such as wood.
Sediments have a range of sizes, from largest
The key to
learning how clastic
However, there are
is by of
looking at what
sediments. I shouldmakes
These rocks are
sediments that are
-Silt, by time and
We sort the sediments by
size using a sieve.
-Sediments are placed into
the top sieve,
-The lower sieves have
screens to screen out the
-Once the system is turned
on, the sieve vibrates.
-After several minutes, we
can see the different
sediments, sorted by size.
Nature also sorts sediments.
-In rivers, fast moving waters carry all
-As the rivers slow down, or approach
the edge of the riverbed, sediments
are dropped off.
-The largest and heaviest (pebbles)
get dropped off first.
-The smallest (clay) stay in the river
-Dissolved minerals in the ocean
or river water act as cement that
holds the sediments together.
-Silica, lime, and iron can act as
-The cement works its way into the
pores and irregularities in the
-The cement binds to the rock
sediments and holds them
-Clays and silts can bind together when pressure is high enough,
but heavier materials need cement to hold them together.
-Pebbles and gravels form a conglomerate.
-Sand forms sandstone.
-Silt and clay forms shale.
-Conglomerate is the coarsest
of the clastic sedimentary rocks.
-The pebbles and gravels that
make up the conglomerate are
easily visible to the naked eye.
-Conglomerates can be made out of any type of pebble or gravel.
-Quartz is very commonly found in conglomerates because of its
-The cement that holds the pebbles and gravels together is usually
very fine grained.
-Sandstone is made of sand
-Generally, all the sand
sediments are quartz grains.
-Cement holds the sand grains
-Because the cement never fills all the spaces between the sand
grains, there can be up to 30% of air space between the grains.
-Sandstone is rough, gritty and durable.
-In some areas of the world, sandstone was commonly used as a
building material and as a sculpting material.
-Shale is made of clay and
-Clay is composed mostly of
kaolin, so shale is mostly
-The grains in shale are very
tightly packed together.
-Shale is a very soft and smooth stone.
-It breaks very easily.
-Fossils are found in shales, since they form in rivers.
Some sedimentary rocks form
through chemical processes.
-When minerals are dissolved in
a new material.
-Limestone forms from tiny grains of of calcite.
-Calcium can also come from shells or bones.
-The tiny grains of calcite are usually deposited from sea or lake
-Limestones are usually light
gray or white in color.
-Due to the heavy nature of the
atoms that make the minerals,
limestone is very dense.
-Limestone will feel smooth to
-Rock salt is the natural form of
-Rock salt is made almost
entirely out of halite.
-Rock gypsum is very much like
rock salt, but made out of
-Both form through the
evaporation of salt lakes or
ocean bays cut off by sandbars.
-Limestone can also form through
Now, there is one last type of
-Shells of sea creatures, plankton,
sedimentary rock we should look
bones, etc. pile up on the ocean
at, and that is sedimentary rocks
that form through organic means.
-As time progresses, these calcium
deposits compact into limestone.
-On land, a common sedimentary
rock is formed from plant remains:
-Sedimentary rocks show
special features that help to
-One method we use is
-Stratification is the
arrangement in visible layers.
-How does stratification
-When a change of sediments occurs, a new layer develops.
-Different size grains, or new sediments appear, a new layer of
sedimentary rock forms.
-This is how sedimentary rocks become stratified.
-Aha! New sediments result in
-That’s why we see sandstone
on top of shale, on top of
-Now, there are a couple other
features we can look at:
bedding planes and cross
-Bedding plane: horizontal
layers where stratification
-Cross bedding: A angled
section or layer in stratification.
-It can be due to wind, erosion,
or tectonic forces.
-Many sandstones show ripple marks on the surface of the
-These formed by the winds and water that formed and deposited
-Mud cracks develop when deposits of wet clay dry out and
-In a bedding plane, these cracks are filled with other materials.
-Limestones can sometimes
contain hollow spheres of
-These hollow spheres
-This is a geode.
-It appears that geodes
formed by water wearing
away a hallow in the stone.
-Over time, this hallow gets
quartz deposited in it, which
grows into crystals.
-Also in limestones, there
can be lumps of chert or flint.
It’s sedimentary, my dear
How do you know so much
about these rocks, Mr.