Rock Identification Lab
At this point you should have a good understanding of the rock cycle and the forces/processes that
change rocks. You should also have a basic understanding of the characteristics used to classify rocks
within the three main groupings of rocks: igneous, sedimentary and metamorphic.
Now you are going to attempt to use that information to first classify 12 rocks one at a time into the 3
main groups, and then identify individual rock names. You might want to review Chapter 5, section 1,2,3
and 5, paying particular attention to the pictures and the classification tables (tables 1, 2 and 3).
Objective:
To categorize major rock types and subsequently to classify 12 rock samples using a dichotomous key.
Materials:
12 rock samples
dropper bottle of dilute HCl
hand lens
glass microscope slides (for scratch test)
paper towels
safety goggles
6 bonus samples
Procedure:
1) You and your partner will receive one of the rocks. Using the clues sheet accompanying this lab,
identify the basic rock type. Observe its texture, color, crystal size and composition with and without
the hand lens. Record your observations in the data table.
2) Repeat the above for each of the 12 rocks, describing the characteristics, but only identifying the
type at this point. You will move stations (1 to 2, 2 to 3….12 to 1) after approximately 2 minutes of
recording detailed observations and determining the rock type, which you will also record in the
table.
3) Once completed with your initial observation, obtain a complete set of the samples in one box.
4) Use the Dichotomous Keys for each of the 3 types of rocks, based on the rock type you selected.
Begin by reading each statement and choosing whether the answer is yes or no, based on the
characteristics and observations of the rock you have selected first.
5) Continue working through the key in this way until you come to a statement that allows you to
classify your sample rock. Record the name and # of the rock, as well as a brief justification for your
choice in the table. Should you be instructed to go back to the beginning and start again, be sure that
you have correctly identified the main type of rock, and then proceed from the beginning of that key.
7) When you arrive at the statement indicating to use HCl, be sure to put on goggles and get a paper
towel, as well as a bottle/flask of dilute HCl. Use the HCl (dilute hydrochloric acid) to test whether the
rock reacts (effervesces) by adding 2 drops onto the surface of the rock, which is sitting on a paper
towel. Then blot the HCl off of the rock, and return it to the correct place in the box. Be sure to throw
out the paper towel and return your goggles.
DATA TABLE
Sample
Description
#
1
2
3
4
5
6
7
8
9
10
11
12
Rock Type
Identification
Rock Name and #
Justification?
Analysis and Conclusions—Record all answers on a separate sheet of paper and attach.
1) Compare your results to one other group. Do their results support or not support yours? What was
different?
2) How difficult was it to use the classification key and tables to identify your rocks? What problems did
you encounter?
3) How useful was rock color in classifying the rock samples? Explain.
4) Which two rock samples were the easiest to identify? What properties made it easy?
5) Which two samples were hardest to identify? Why?
Extension Activities/Extra Credit (Time permitting):
1.) Develop your own dichotomous key (or a classification system, flowchart or graphic organizer of
your choice) for the following six samples of rocks: pumice, rituminous, slate, anthractite,
diorite and fossilized limestone. Be sure to include the terminology that we have learned thus
far (including extrusive/intrusive, foliated/nonfoliated, clastic/chemical/organic.). If another
group is finished, see if you can trade keys and use the key to classify the 6 rocks. Include the
key, filled out, on a separate sheet of piece of paper, and be sure to explain why this process is
useful for classifying and why it was difficult to develop the key yourselves.
OR
2.) Take the 12 specific rock types and research on your own (at home) to make a chart/list/graphic
organizer, to provide all information about that rock including: clastic/organic/chemical,
extrusive/intrusive, foliated and non-foliated.