Mineralogy is the systematic study of minerals, the materials of which the rocks of the earth's crust are made. It excludes the study of substances resulting from the processes of plant and animal life, such as COAL, OIL, AMBER, PEARL, and animal bones. While such substances are often listed under mineral resources, they are not true minerals, but rather are complex mixtures.
   Mineralogy is one of the very old sciences. During the STONE AGE, man knew about, and used, minerals. By the Bronze Age, man was familiar with the process of smelting, to obtain metal from natural compounds.
   With the invention and development of new techniques of mineral study and the rapid discovery of new minerals, the accumulating data on the subject of minerals and mineralogy has grown to tremendous proportions. At present, there are many specialized classifications, or fields, of mineralogy, some of which are sub-classified further. The four principal branches of this science, however, are crystallography, physical mineralogy, optical mineralogy, and chemical mineralogy.