Although the symmetry elements are not sufficient to identify the mineral, you will soon be able to recognize that the symmetry observed implies that this mineral belongs to the tetragonal crystal system. The symmetry, together with a measurement of the separation of the spots would be sufficient to identify this diffraction pattern as belonging to the mineral vesuvianite. The image shown on the left was taken with a high resolution TEM similar to the one shown in Figure 1.10 of your textbook. The dark areas represent hollow channels through the structure while the white spots can be equated with regions of high atomic density. Note the periodicity and the symmetry.
Minerals are the basic building blocks of all rocks.
Many minerals have economic value. Many minerals are important in modern industry, health and political activities. A knowledge of mineralogy is required for an understanding of rocks, and hence for an understanding of how the earth and other planets operate. Virtually all aspects of geology are fundamentally tied to mineralogy. We will talk a lot about chemistry, molecular structures, geometrical relationships and symmetry.