Laboratory Manual for Introductory Geology 4e

most familiar. Identifying unknown minerals is easiest if you follow the systematic
approach used by geologists.
STEP 1 Assemble the equipment available in most geology classrooms to study
minerals:
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■
■
■
■
A glass plate, penny, and knife or steel nail to test hardness
A ceramic streak plate to test streak and hardness
A magnifying glass, hand lens, or microscope to help determine cleavage
Dilute hydrochloric acid to identify carbonate minerals
A magnet to identify magnetic minerals
STEP 2 Observe or measure each mineral specimen’s physical properties. Profile the
properties on a standardized data sheet like those at the end of the chapter, as
in the example in TABLE 3.2.
TABLE 3.2 Sample profile of a mineral’s physical properties
Specimen
number Luster Color Hardness Breakage Other diagnostic properties
1 Metallic Dark gray Less than a
fingernail
Excellent cleavage in
one direction
Leaves a mark on a sheet
of paper
STEP 3 Eliminate from consideration all minerals that do not have the properties you
have recorded. This can be done systematically by using a flowchart (FIG. 3.7)
that asks key questions in a logical sequence, so that each answer eliminates
entire groups of minerals until only a few remain (one, if you’re lucky). Or
you can use a determinative table in which each column answers the same
questions, like those at the branches of a flowchart. Appendices 3.1 and 3.2 at
the end of this chapter provide flowcharts and determinative tables. Experiment
to find out which tool works best for you.
Follow these steps to complete Exercise 3.7.
FIGURE 3.7 Flowchart showing the steps used to identify minerals.
Fracture
Softer than a
fingernail
Breakage
One
Other
diagnostic
properties
Luster
Metallic
Dark or
light?
Dark
Light
Hardness
Harder than
a fingernail
Cleavage
Directions?
Marks
paper
Mineral
name:
Graphite
Nonmetallic
Note: For simplicity, only the path for the unknown mineral is shown.
3.5 IDENTIFYING MINERAL SPECIMENS
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