Mineral processing technology. An introduction to the practical aspects of ore treatment and mineral recovery / Технология переработки полезных ископаемых. Введение в практические аспекты переработки руды и извлечения полезных ископаемых

The forms in which metals are found in the crust of the earth and as sea-bed deposits depend on their reactivity with their environment, particularly with oxygen, sulphur, and carbon dioxide. Gold and the platinum metals are found principally in the native or metallic form. Silver, copper, and mercury are found native, as well as in the form of sulphides, carbonates, and chlorides. The more reactive metals are always in compound form, such as the oxides and sulphides of iron and the oxides and silicates of aluminium and beryllium. The naturally occurring compounds are known as minerals, most of which have been given names according to their composition (e.g. galena—lead sulphide, PbS; sphalerite—zinc sulphide, ZnS; cassiterite—tin oxide, Sn02 ).
Minerals by definition are natural inorganic substances possessing definite chemical compositions and atomic structures. Some flexibility, however, is allowed in this definition. Many minerals exhibit isomorphism, where substitution of atoms within the crystal stucture by similar atoms takes place without affecting the atomic structure. The mineral olivine, for example, has the chemical composition (Mg, Fe)2Si04, but the ratio of Mg atoms to Fe atoms varies in different olivines. The total number of Mg and Fe atoms in all olivines, however, has the same ratio to that of the Si and O atoms. Minerals can also exhibit polymorphism, different minerals having the same chemical composition, but markedly different physical properties due to a difference in crystal structure. Thus the two minerals graphite and diamond have exactly the same composition, being composed entirely of carbon atoms, but have widely different properties due to the arrangement of the carbon atoms within the crystal lattice. The term "mineral" is often used in a much more extended sense to include anything of economic value which is extracted from the earth. Thus coal, chalk, clay, and granite do not come within the definition of a mineral, although details of their production are usually included in national figures for mineral production. Such materials are, in fact, rocks, which are not homogeneous in chemical and physical composition, as are minerals, but generally consist of a variety of minerals and form large parts of the earth's crust. Granite, for instance, which is the most abundant igneous rock, i.e. a rock formed by cooling of molten material, or magma within the earth's crust, is composed of three main mineral constituents, feldspar, quartz, and mica. These three homogeneous mineral components occur in varying proportions in different parts of the same granite mass. <...>