Mineralogy

MINERALOGY (from Latin minera—piece of ore, rock specimen, and Greek logos—teaching, word), the science of minerals, their chemical composition, physical properties, conditions of formation in nature, and changes and transformations in connection with the change of these conditions. Minerals are solid, liquid, and gaseous natural bodies. Their composition is expressed by a chemical formula. By physical structure, they often represent crystalline substances and are sometimes found in the form of crystals. The geometric and physical properties of such substances are studied by crystallography (the science of crystals), crystal optics, and other branches of physics. Minerals are significant as mineral resources. Millions of tons of various metals are smelted from them. The basic chemical industry obtains tens of millions of tons of salts and other chemical products from minerals. Minerals are used in medicine in rare cases directly (for example, minerals from the salt group), but mainly as products of their processing. The following minerals belong to this category. Native sulfur; sulfur flour (sublimed sulfur), obtained by the sublimation of native sulfur; it has applications in veterinary medicine. Native bismuth and bismuth glance serve as the basis for obtaining bismuth preparations, especially white bismuth, a widely used medicinal agent. Realgar and orpiment (sulfide salts of arsenic) are the raw material for arsenic preparations. Cinnabar (mercury sulfide) is a source of mercury compounds. Potassium permanganate is obtained from pyrolusite (manganese oxide). White magnesia and other magnesia salts are obtained from the mineral magnesite or from the brine of salt lakes and estuaries, where magnesium is found in the form of magnesium chloride and is easily extracted. Borax and boric acid are obtained from natural compounds of similar composition found in lakes associated with volcanic activity. Glauber's salt is found in large quantities in lakes and sea lagoons. Furthermore, it is necessary to note the soft mineral—talc, the powder of which is known in medicine as talcum powder. Radium preparations are obtained in the USSR from the mineral tyuyamunite, found in Turkestan, which is a uranium vanadate. Known deposits in Czechoslovakia consist of beds of pitchblende, which is primarily uranium oxide. Relatively few minerals are used directly in the form in which they are extracted from the earth—corundum, diamond, asbestos, mica, graphite, etc. Most minerals undergo fundamental processing before finding application in science or technology. The practical significance of mineralogy lies in the fact that, by studying the properties of minerals, it leads to the discovery of new mineral resources and to the best use of those already known. By studying the conditions of mineral formation in nature, mineralogy helps in the discovery of new mineral deposits and the clarification of their industrial significance. For a long time, mineralogy was a descriptive science. Its goal was the description of the external form and properties, chemical composition, and location of minerals. The successes of geology in the 18th century and chemistry in the early 19th century were reflected in mineralogy; a view of it as the chemistry of the earth's crust appeared (Berzelius); more attention began to be paid to the conditions of mineral occurrence in nature (Werner), as well as their joint occurrence, paragenesis (Cronstedt, Breithaupt), but this trend did not receive further development and stagnated for several decades. In the first half of the 19th century, mineralogy was characterized mainly by two directions—crystallographic and chemical-analytical. Thanks to the discovery by Abbé Haüy of the geometric law of crystallography (law of parameters), an exceptional interest in questions of formal crystallography appeared in mineralogy. Minerals began to be subjected to careful measurement to establish crystallographic forms. The successes of analytical chemistry caused an equally formal interest in the chemical composition of minerals on the part of prominent chemists. Mineralogy entered a new era in the second half of the 19th century. The development of mining (especially in America) and the strengthening of interest in it were the reasons for the tendency that appeared in mineralogy to transfer questions of mineralogical research to the setting of field observations. Modern mineralogy has retained an interest in individual minerals and continues their comprehensive study, but in addition, it also studies the very processes of their formation. Minerals are now understood as products of natural reactions. Mineralogy strives to predict the appearance of minerals from a consideration of a given set of phenomena and, conversely, to establish the process itself from the observation of minerals in nature. Paragenesis, age relationships between minerals, changes in their composition depending on the form of occurrence in nature, the character of mineral destruction, etc., have again acquired special significance. Not satisfied with questions of the origin of minerals, mineralogy deepens its tasks in the direction of geochemistry, i.e., it studies the laws of the distribution of chemical elements in the earth's crust, the reasons for the joint occurrence of elements and their groupings, dispersion, and concentration. In Russia, the tasks of mineralogy were already widely understood by M. V. Lomonosov. In the mid-19th century, the crystallographic trend that dominated mineralogy was represented by Koksharov, and questions of mineral analysis were resolved by the greatest analysts, such as Hermann, Gadolin, and others. Mineralogy with its modern understanding of tasks was born in Russia at Moscow University in the 90s. Its founder should be considered V. I. Vernadsky, who created a large school of mineralogists of the geochemical trend there. In the works of V. I. Vernadsky himself, a special place is occupied by the role of the biochemical process in the surface zone of the earth's crust. An outstanding representative of this trend was Ya. V. Samoilov, who established the concept of a biolith, by which he meant any mineral connected in its origin to the vital activity of organisms. In recent years of intensive prospecting and exploration work, an increased interest in mineralogy has been noticeable in the USSR, especially regarding questions of the genesis of mineral resources and geochemistry. The study of questions of mineral genesis has been advanced mainly by N. M. Fedorovsky. A representative of the geochemical trend is A. E. Fersman. In its content, mineralogy is divided into two parts—genetic and descriptive mineralogy. In a brief overview, the data of genetic mineralogy are presented in the following form. Phenomena of mineral formation are studied within the limits of the surface zone of the earth's crust to a depth of 16 km. The studied area includes the lower layers of the atmosphere. The petrographic composition of the lithosphere: igneous rocks 95%, schists 4%, sandstones 0.75%, and limestones 0.25%. The gross chemical composition of the entire earth's crust to the indicated depth, including the atmosphere, is as follows (in %): O 49.20, Si 25.67, Al 7.50, Fe 4.71, Mg 1.93, Ca 3.39, Na 2.63, K 2.40, Ti 0.87, C 0.58, Cl 0.08, Others 0.19. The attached schematic cross-section presents the various thermodynamic zones of the earth's crust (Figure 1). I. Surface weathering zone. Characterized by low pressure and temperature. Chemical reactions proceed with the participation of aqueous solutions, O, CO₂, and the vital activity of organisms. II. Deep weathering zone. Somewhat elevated temperature and pressure. Reactions occur in aqueous solutions with the participation mainly of carbonic acid. III. Cementation zone. Even higher pressure and temperature. The precipitation of minerals predominates over dissolution. IIIj. Diagenesis zone presents special conditions under which the formation of solid sedimentary rock from clastic material occurs under a layer of seawater. IV. Crystalline schist zone. Characterized by high pressure and temperature, and the absence of free O and water. Silica displaces carbonic acid from its compounds under the conditions of this zone. Minerals are created by the method of recrystallization of other minerals unstable in this zone. V. Magma zone. Region of molten matter at high pressure and temperature, of complex silicate composition. Formation of igneous rocks. V₁. Region of mineral formation in rock fractures due to substances released during the solidification of magma. Pegmatite veins of special genesis and mineralogical composition. Ore veins. V₂. Formation of contact areas. Interaction of magma with foreign rocks. The study of the question of the distribution of chemical elements in the earth's crust leads to the conclusion that the deepest parts of the magma are rich in iron, chromium, and magnesium—they correspond to basic igneous rocks. The marginal parts of the magma, on the contrary, are rich in silica and alkalis and poor in iron, magnesium, and partly calcium. The corresponding rocks are acidic, of the granite type. Figure 2 gives an idea of the zonal distribution of chemical elements in a vertical section in connection with intrusions, granite intrusions.

The symbols of chemical elements on the drawing indicate the presence at a given point of conditions favorable for the formation of corresponding minerals. Thus, magmatic minerals are distinguished—containing Zr, Ta, Nb, etc.; contact minerals—containing Fe, Cu, Ti; vein minerals of deep horizons—containing Sn, W, Mo; of intermediate horizons—Cu, Pb, Zn; and of upper horizons—containing Sb, As, Hg. In general, all minerals are stable under the conditions of their formation, with the change of which they undergo transformation, decomposition, and alteration. Cyclic processes are of great importance in Mineralogy, when minerals, after a series of changes, can be regenerated at the expense of the products of their own destruction. Descriptive Mineralogy examines minerals in the order of some classification. The chemical classification of the American mineralogist Dana enjoys the greatest recognition. In it, minerals are distributed by chemical composition into the following groups: native elements, sulfur compounds, halides (compounds of metals with Cl, Br, F), oxides, carbonates (salts of carbonic acid), silicates, phosphates, sulfates, and some others. In genetic classification, minerals are united into groups according to the similarity of genesis conditions; such, for example, are minerals resulting from the drying up of marine basins—common salt, gypsum, potassium salts, etc. Another example is the group of bioliths—phosphorite, bog iron ore (the vital activity of Leptothrix ochracea), saltpeter (some cases), iron pyrite (some cases), coral calcite (CaCO₃), etc. In descriptive mineralogy, the physical and chemical properties of minerals are studied. Some of the properties are of great interest and are the reason for the practical use of minerals (the hardness of diamond and corundum, graphite, mica, etc.). In addition, it notes the conditions of genesis, associates, decay products, deposits, practical application of minerals, etc. The total number of minerals is about 1,000, and counting varieties—about 3,000. Every year, about 50 new minerals (with varieties) are discovered. Along with extremely common minerals, for example, quartz (about 12% by weight of the lithosphere) and feldspars (about 57%), there are also very rare ones, known in only a few specimens. Also, in a practical sense, besides minerals of great importance, there are known minerals that do not yet have application. In its research, Mineralogy uses field observations and data and methods of the sciences: geology, physics, chemistry in the broad sense of this word—analytical, physical, colloidal, and even biochemistry. Crystallography in modern Mineralogy has an auxiliary significance. Essentially, crystallography, now understood as the physics of solid matter, has moved to physics. Two major Russian scientists—E. S. Fedorov and G. V. Wulff—played a role in setting new, purely physico-chemical questions that separated crystallography from mineralogy. The optical method of studying minerals in thin sections under a microscope in polarized light, discovered in the mid-19th century, has acquired great importance in the study of rocks, as has the recently developed method of investigation in reflected light in the study of ores. Methods of mechanical and thermal analysis are widely used. The former consist of separating minerals with the help of heavy liquids, elutriation, magnetic separation, flotation, etc.; the latter—in observing and studying the changes occurring in a mineral when heated to high temperatures. For this, recording instruments are used, making it possible to register the course of changes in the form of a continuous curve. Questions and methods of artificial reproduction of minerals in the laboratory to clarify natural conditions of genesis are acquiring increasing importance. For the same purpose, the equilibrium conditions of various artificial physico-chemical systems are studied. Observation data here are also usually presented in the form of diagrams and curves. The teaching of Mineralogy in the past was set up at universities and mining higher education institutions, where there were departments of mineralogy and mineralogical institutes. With the reform of higher education, the teaching of Mineralogy was concentrated in mining technical institutes and technical schools. The teaching method is active. For students, field and production practice at mining enterprises and in geological prospecting parties is mandatory. Corresponding educational and scientific institutions in the USSR are built on the principle of combines. According to such a plan, for example, the Geological Prospecting Combine under the Main Geological Prospecting Administration of the Supreme Council of the National Economy was built. Mineralogical institutes and departments of Mineralogy of the former Moscow University and the Moscow Mining Academy merged into it. The Geological Prospecting Combine includes a workers' faculty, a geological prospecting technical school, a geological prospecting institute, and a research institute. In addition, there are mineralogical institutes at production and industrial enterprises (associations). Their task consists of scientific assistance to enterprises. Work in research institutes is built on the principle of the complex method so that, as a result of a comprehensive study of mineral resources, ways of their best use can be indicated, and in terms of genesis questions, data can be obtained for the most rational organization of prospecting and exploitation work. The largest research institutes of Mineralogy are the Institute of Applied Mineralogy and the State...

Figure 2. Ideal cross-section through the earth's crust in the region of granitic magmas and associated geochemical processes.

Institute of Non-Ferrous Metals in Moscow. At the Communist Academy in Moscow, there is an Institute for the Genesis of Minerals and Rocks, and attached to it is a synthetic laboratory for conducting experiments on the artificial production of minerals. Scientific mineralogical questions are widely posed and deeply studied at the Mineralogical Museum of the Academy of Sciences. In the USSR, there is a scientific mineralogical society, founded in 1830, which has its own organ ("Notes of the Russian Mineralogical Society," Moscow, since 1870).