Identification of minerals in hand specimens is the main emphasis of this chapter. The methods used are careful visual evaluation and basic tests with easily available tools. Only at the end of this chapter do we briefly introduce some sophisticated instrumental methods that are used in the quantitative characterization of minerals and other crystalline solids. Chapter 6 is devoted to the study of minerals with a polarizing optical microscope.
The identification of an unknown mineral in a hand specimen begins with making observations that allow us to assess a specimen’s overall form (or crystal habit if it is well crystallized), state of aggregation, and color. Those properties that allow us to identify a mineral or at least narrow down the possibilities are said to be diagnostic. Color is probably the first property the observer sees, followed by the overall shape of the mineral. But, though instantly noted, color is not a reliable diagnostic property in most minerals, because many (chemically variable) mineral groups exhibit a range of colors.
Important physical properties that characterize a mineral and allow us to separate one from another in hand specimens are the following:
State of aggregation
Specific gravity (or relative density)
Each of these properties is discussed in this chapter, but it must be recognized that the actual process of mineral identification is best learned in the laboratory part of the course you are enrolled in. There you will tune your observational skills through the study of labeled mineral specimens as well as unknowns. Here, we first introduce those properties that can be evaluated by observation only – habit, state of aggregation, color, and cleavage – and subsequently discuss properties such as hardness, specific gravity, magnetism, radioactivity, and solubility in hydrochloric acid, all of which require testing tools.