Sedimentary Rocks
Sedimentary rocks form from particles deposited by water and wind. Sand grains, mud, and pebbles are
some of the sediments that form sedimentary rock. Sediment is small, solid pieces of material that come from
rocks or living things.
Weathering occurs when running water or wind loosen a piece of rock. Erosion occurs when the
sediment is carried away. Eventually, the moving water or wind slows and deposits the sediment. Deposition is
the process by which sediment settles or drops out of the water or wind carrying it. After sediment has been
deposited, the processes of compaction and cementation change the sediment into sedimentary rock. At first the
sediments fit together loosely. But gradually, over millions of years, thick layers of sediment build up. These
layers are heavy and press down on the layers beneath them. Then compaction occurs. Compaction is the process
that presses sediments together. Year after year more sediment falls, creating layers. The layers often remain
visible in the sedimentary rock. While compaction is taking place, the minerals in the rock slowly dissolve in the
water. Cementation is the process in which dissolved minerals crystallize and glue particles of sediment together.
There are three major groups of sedimentary rocks: clastic rocks, organic rocks, and chemical
rocks. Most sedimentary rocks are composed of broken pieces of other rocks. A clastic rock is a sedimentary
rock that forms when rock fragments are squeezed together. Clastic rocks are grouped by the size of the rock
fragments of which they are made. One common clastic rock is shale, which forms from tiny particles of clay.
Sandstone is a clastic rock formed from the compaction and cementation of small particles of sand. Some
sedimentary rocks contain a mixture of rock fragments of different sizes, including conglomerate and breccia.
Organic rock forms where the remains of plants and animals are deposited in thick layers. Two important
organic rocks are coal and limestone. Coal forms from the remains of swamp plants buried in water. Over
millions of years, they slowly change into coal. The hard shells of living things produce limestone. These shells
collect on the ocean floor. Over millions of years, compaction and cementation of shell particles produce
limestone.
Chemical rock forms when minerals that are dissolved in a solution crystallize. For example, a type of
limestone can form when calcite dissolved in water comes out of solution and crystallizes. Chemical rocks can
also form from mineral deposits left when seas or lakes evaporate. For thousands of years, people have used
sandstone and limestone as building materials. Both types of stone are soft enough to be easily cut into blocks or
slabs. Limestone is also used in making cement.
COMMON SEDIMENTARY ROCKS
Sedimentary Rock Type
Organic Sedimentary Rock:
formed from the remains of
living things such as plants
and animals
Chemical Sedimentary Rock:
formed when elements that
were dissolved in water come
out of solution
Particle size or composition
If the rock is made up mostly of shells
Rock Name
Limestone
If the rock is made up mostly of plant and animal
remains
Sediment particles too small to be seen with the
unaided eye. If the mineral material that comes out
of solution is:
calcite-----the rock is………………….
dolomite-----the rock is……………….
halite-----the rock is…………………..
gypsum-----the rock is………………..
Name and size of particles:
Boulder-sized (greater than 256mm)…
Cobble-sized (64-256 mm)…………...
Pebble-sized (2-64 mm)………………
Sand-sized (0.06-2mm)……………….
Clay-sized (less than 0.06 mm)……….
Coal
(bituminous)
Clastic/detrital Sedimentary
Rock: formed when the
particles that are weathered
from other rocks are cemented
together to form a new rock
(also called fragmented rocks)
76 Unit 1 Resources Science Explorer Earth Science
ThinkQuest http://library.thinkquest.org/J002289/meta.html
Limestone
Dolomite
Rock Salt
Gypsum
Conglomerate
Conglomerate
Conglomerate
Sandstone
Shale
Name:
Date:
Sedimentary Rocks Identification Activity
Class:
1.
Draw the Sedimentator and what is inside. Then label the following on your diagram. (rock, sand, soil, water)
2.
If these sediments (rock, sand, soil, leaves) were found in the Earth, layered just like this Sedimentator, which of the
sediments are probably the oldest? Why?
3.
What do you think causes the sediments to settle (layer) the way they do?
4.
Describe what happened when the Sedimentator was left overnight?
5.
What might eventually happen to these sediments if left in the earth for 100’s of 1000’s of years?
6.
Look at the rock samples. Which material in the sedimentator might have made the rocks? (leaves, rock, sand)
a. Conglomerate –
b. Sandstone –
c. Coal –
7. Observe the five samples of sedimentary rocks. Use the chart on your tray to assist with completing the chart below.
Then make one quantitative observation and two qualitative observations per sample. Clean-up.
Name of
Description
Type of
M
Rock
Sedimentary
Density
Two other properties
V
Sample
Rock
A
B
The sediment particles of calcite
are formed by chemical
precipitation & are too small to
see with an unaided eye.
The sediment particles are
mixtures of sizes that range
between 3.0 & 20.0 mm.
1
1
2
1
1
2
C
1
1
Organic
Limestone
D
2
The sediment particles are sandsized.
1
1
2
E
A rock made up mostly of plant
and animal remains.
1
1
2
8. What were the five steps needed for each of the above rocks to become sedimentary rocks?
9. What is the difference between clastic, organic, and chemical rocks?