Laboratory Manual for Introductory Geology 4e

EXERCISE 3.2
Is It a Mineral or a Rock? (continued )
Name:
Course:
Section:
Date:
Mineral 2:
Mineral 3:
Mineral 4:
3.4 Physical Properties of Minerals
Mineralogists (geologists who specialize in the study of minerals) have named
more than four thousand minerals that differ from one another in chemical composition
and crystal structure. These characteristics determine a mineral’s physical
properties, which include how it looks (color and luster), breaks, feels, smells, and
even tastes. Some minerals are colorless and nearly transparent; others are opaque,
dark colored, and shiny. Some are hard, others soft. Some form needle-like crystals,
others blocky cubes. You instinctively used some of these physical properties in
Exercise 3.2 to decide the number of minerals in your rocks and then to describe
them. In this section we will discuss the major physical properties of minerals so
that you can use them to identify common minerals—in class, at home, or while
on vacation.
3.4.1 Diagnostic versus Ambiguous Properties
Geologists use physical properties to identify minerals much as detectives use
physical descriptions to identify suspects. And, as with people, some physical
properties of minerals are diagnostic properties—they immediately help identify an
unknown mineral or rule it out as a possibility. Other properties are ambiguous
properties because they may vary in different specimens of the same mineral. For
example, color is a notoriously ambiguous property in many minerals (FIG. 3.1).
Size doesn’t really matter either; a large specimen of quartz has the same properties
as a small one. Exercise 3.3 shows how diagnostic and ambiguous properties
affect everyday life.
3.4 PHYSICAL PROPERTIES OF MINERALS
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