Sedimentary Rock Identification
Introduction:
Sedimentary rocks are formed from accumulated sediments. Most sedimentary
rocks are formed from materials that have been deposited in calm water. Often some of
the characteristics of the sediments are retained in sedimentary rocks. Geologists have
classified the sedimentary rocks into three groups: clastic, chemical, and organic. See the
“Scheme for Sedimentary Rock Identification” in your Earth Science Reference Tables.
Objectives: When you have completed this investigation, you should be able to:
1. Recognize sedimentary type rocks and
2. Identify several common sedimentary rocks.
Materials:
Conglomerate
Shale
Magnifying Lens
Halite
Chemical Limestone
Dilute Hydrochloric Acid
Sandstone
Coquina
Bituminous Coal
Procedure: There are clues written into the directions. Read carefully to find the
clues.
1. Your team will receive a set of sedimentary rocks. By carefully observing the
samples and discussing them with your team, divide the samples into 3 groups
according to the chart below:
Group 1
Clastic
Group 2
Chemical
Group 3
Organic
Those which contain round
or angular pebbles and
fragments of other rocks, or
sand size grains or very fine
grains or flakes
Those which contain
crystals which you can see
with or without a
magnifying lens; or is
monomineralic; or often
looks like it has layers.
Those which contain tiny
visible shells or which look
like coral
2. Raise your hand and wait patiently until your teacher can get to your team to
check your groupings. If your groupings are right, go on to step 3. If your
groupings are wrong, try again.
3. Start with Group 1. Record clastic in the Report sheet in the “Clastic, Chemical
or Organic” column for each sample in Group 1.
4. For each sample of that group, determine and record the composition. Choose
from the following compositions:
Silicate
Carbon
Evaporite
Carbonate
Evaporite or
Carbonate
Those that contain fragments of quartz, feldspar, mica or
other silicate minerals. You may be able to see pieces of
sand or pebbles.
Those that contain carbon from plant remains. These
will probably make a blackish mark on your paper.
Those that contain minerals that were left when water
evaporated. There may be very small crystals giving it a
finer texture.
Those that contain calcite from animal remains (like
bones or shells). The calcite will bubble and fuzz when
hydrochloric acid is added. Raise your hand when you
think you need to do the acid test. You must explain to
your teacher what observations you made that made you
think it was a carbonate.
Can be formed either by evaporation or from organic
remains.
5. For each sample of the same group, record the method of lithification.
Lithification refers to the process by which loose sediments are changed into solid
sedimentary rocks. Carefully, with lots of thought, chose from the following
methods of lithification: YOU MUST RECORD ALL OF THE WORDS IN
BOLD PRINT!!!
Precipitation from evaporating water
Compaction and cementation of
marine derived sediments
Compactionn and cementation of
land derived sediments
Compaction and cementation of
organic material
When water evaporated, the minerals
that were dissolved settled to the
bottom.
When sea animals die, their shells settle
to the bottom and eventually are
packed tightly together are cemented or
“glued”
When broken pieces of rock (sediments
and fragments) are packed together and
are cemented of “glued”
When plants die, their remains are
packed together and are cemented or
“glued”
6. Identify each sample in Group 1 using the following clues and record. Each rock
name is used only once. Some names will not be used.
Bituminous Coal = organic; composed of carbon; formed by compaction and
cementation of organic material.
Conglomerate = clastic; composed of silicate; formed by compaction and
cementation of LARGE land derived sediments.
Coquina = organic; carbonate; formed by compaction and cementation of marine
derived sediments; will bubble and fizz when hydrochloric acid is added.
Halite (rock salt)= chemical; evaporite or carbonate; formed by precipitation from
evaporating water; will bubble and fizz when hydrochloric acid is added.
Limestone= chemical; ecaporite or carbonate; formed by precipitation from
evaporating water, will bubble and fizz when hydrochloric acid is added.
Sandstone = clastic; silicate; formed by compaction and cementation of SAND
SIZED land derived sediments.
Shale = clastic; silicate; formed by compaction and cementation of
MICROSCOPIC land derived sediments.
7. When you think you have identified all of Group 1, raise your hand and wait
patiently for your teacher to get to your team. If all of your identification are
correct, go on to step 8. If your identification are not correct, repeat steps 4
through 7.
8. Do Group 2 by recording chemical on the Report Sheet in the “Clastic, Chemical
or Organic” column for each sample in Group 2.
9. Repeat steps 4 through 7 for each sample in Group 2.
10. Do Group 3 by recording chemical on the Report Sheet in the “Clastic, Chemical
or Organic” column for each sample in Group 3.
11. Repeat steps 4 through 7 for each sample in Group 3.
12. It is the responsibility of your team to wipe off your tabletop and to properly put
the materials away.
13. Complete the lab report.