Vol 12 Iss. 2

In the present paper the author gives an example of application of his method to the study of the chemistry of rocks by means of diagrams (ref. 1). Here this method is applied to the study of the rocks of Somma and Vesuvius, chiefly according to the data recently published by Rittmann (ref. 6). Fig. 3 in this paper is a diagram of the chemical compositions of these rocks represented by means of vectors. The letter S0 designates trachyte of the Ur-Somma. S1 — products of ancient Somma. S2 — formations of the Young Somma before the historic eruptions. S2′ — products of the historic Young Somma and finally V — products of the activity of Vesuvius. The diagram shows that for every cycle of eruptions the vectors conspicuously change their position corresponding to the considerable change in the chemical composition of eruption products of every cycle. Passing from one cycle to another, we see a displacement of the vectors whose initial points for each cycle are joined together by a dotted line. This displacement goes from left to right, and its direction characterises the type of evolution of the magma in the hearth. Thus in the given example it becomes obvious that there are two directions to distinguish in the position of the vectors: one of them, the more strongly marked, represents differentiation, which takes place in the cycles between paroxysms of the activity of a volcano; the other corresponds to the general change in the chemistry of the magma in the hearth.

In this paper are described different modes of making drawings of a petrographical thin section, with many practical hints. The authors think that the best practical method is to draw after a magnified microphotograph and then to etch the photo.

In 1935 the author was making geological explorations in the upper course of the Zeravshan River which flows through the territory of the Tadjik SSR. During these works he was able to visit the outcrops of alkaline rocks in the region of the upper waters of the river Tagoba-Sobak (fig. 1). The coordinates of the outcrop of the alkaline rocks are as follows: Longitude 69° 40′ E (from Greenwich), latitude, 39° 45′ N. The alkaline rocks of the outcrop in question had been visited previously by several explorers, and they are described with sufficient details in a paper by M. A. Preobrajensky, published in 1911 (8). Yet the field observations of the author of the present paper and the microscopic examination of thin sections of the rocks collected suggest somewhat different ideas concerning the genesis of the alkaline rocks of Tagoba-Sobak in contradiction to the data published in special literature. This circumstance induced the author to put the materials in his possession to a more detailed study the conclusions whereof are briefly set forth below.

The presence of hornblende in slags is of great interest to mineralogists, petrologists and metallurgists. In the studied titaniferous slags, either no mineral is found that is similar to the previously described basaltic hornblende or is not amphibole at all, or it turns out that the mineral identified in the first study as basaltic hornblende is actually olivine, a member of the series of isomorphic compounds Mg₂SiO₄ — Fe₂SiO₄ (maybe with admixtures of some other orthosilicate molecules). This shows that all the assumptions that were made above when accepting the presence of amphibole in slags as a fact are incorrect: these titaniferous slags are more refractory and more viscous than the hypothetical slag with basaltic hornblende. With this article I would like to show the importance of the issue of the possibility of crystallization of amphiboles in slags and the need for special careful studies of crystalline formations in slags that are more or less similar to amphibole. It seems that in order to accurately establish the possibility of crystallization of minerals of this group in factory slags, those crystalline precipitates that are identified as amphibole must be examined with X‑rays.

The collected material proves with sufficient clarity the widespread development of metasomatic processes at the contacts of large pegmatite veins. The width of the alteration zones and the intensity of the process are directly dependent on the thickness of the vein, and therefore on the reserves of components moving into the host rock. At the contacts of small veins or at some distance from them we encounter light‑colored, granite‑like rocks, so to speak, that have not yet reached the stage of typical lestivarite. Changes in them consist of greater or lesser albitization of the rock, a decrease or disappearance of quartz, and the appearance of alkali bisilicates. The original minerals – orthoclase, biotite and oligoclase – are present in them in greater or lesser quantities. The process of formation of lestivarites at Lestivar is thus a process of alkaline metasomatism with the introduction of alkalis (Na) and alumina, and in the presence of volatiles, mainly water. Owing to these and to the initial composition of the rock, intense albitization occurs, the formation of alkali amphibole further from the contact and aegirine closer to the contact; finally, apatite, eudialyte, and sphene appear near the contact. When the rock is completely replaced, macroscopically white and sugary rocks are formed, often found at Lestivar and in other places of the external contact within fields of migmatites intruded by alkaline pegmatite veins. This metasomatic process is similar to the phenomena of alkaline metasomatism described by Goldschmidt, Brøgger and others in the contact zones of alkaline intrusions.

The fundamental of the paper is a mineralogical characteristic of the pegmatite and quartz veins in the basin of the rivers Kara-su and Ak-su (Hanaka-su) which flow along the northern slope of the Hissar mountain range, in Central Asia. To the paper is annexed a geological map, on the scale of 1:100000, indicating the pegmatite veins described therein. At the beginning of the paper is given a concise outline of the structure of the region. The pegmatite veins explored are situated at different distances from the granitic batholith, and therefore the author considered it necessary to analyze the whole course of the formation of pegmatite minerals in the given region, beginning with high-temperature processes and finishing with those of low temperature. The author proved that in most veins described a posterior hydrothermal phase had overlaid the already formed pegmatitic bodies and that a change of the mineralogical composition of the pegmatite veins had been a consequence of that. Bearing in mind the peculiarities of the mineral-forming processes of the given region the author analyzes in detail all processes of replacement of primary minerals in pegmatites. A number of microphotographs and drawings in the text illustrates these „replacement-textures“ of primary minerals. From an analysis of the peculiarities of the mineralforming process in the pegmatites of the region in question the author comes to the conclusion that the cassiterite content in the veins increases with depth. At the end of the paper the author, taking into consideration the materials studied, gives a general scheme of the development of the pegmatite process which has produced the pegmatite bodies in the region described (chapter entitled „Genesis of pegmatites“). The fundamental idea of this scheme might be successfully extended to the interpretation of the course of pegmatite processes in other regions.

The author establishes a zonal distribution for different groups of mineral waters on the territory of the USSR, based on numerous facts. The author proposes to name the regions of expansion of mineral waters of one or another of the typical groups mineral water provinces. On the territory of the USSR he distinguishes the following provinces (see map). The first province. Waters of hydro-carbonate, alkaline-earths or (infrequently) sodium and admixed waters, cold and thermal, emanating carbonic acid. The zone of aquiferous fissures of medium depth.. The second province. Sodium waters — sulphate, chloride, hydro-carbonate and admixed, thermal, emanating nitrogen or methane. The zone of deep aquiferous fissures. In this province there may be distinguished regions of expansion of waters with a prevalence of chlorine-ion, emanating methane and characterized by a development of rocks of the sedimentary complex. Such are the Caucasus, the southern part of Turkmenia, Sakhalin and Kamchatka, the area of contemporary volcanic waters, zones of the deepest aquiferous fissures. The third province — saline, strongly mineralized waters, cold, weakly emanating nitrogen or methane. The zone of shallow aquiferous fissures. The Boreal area of saline waters, with negative or extremely low positive temperatures, may be especially distinguished. Moreover the scheme shows regions with rare ferruginous, radioactive and other springs and also places quite barren of mineral waters. Finally — regions of indistinct conditions. The main factors controlling the zonal distribution of the provinces of mineral waters on the territory of the USSR are the following: 1) the composition of the earth crust in the given regions, 2) the position of this region towards the Alpidean folding zone, 3) its position with regard to areas of young uplifts and subsidences, 4) volcanism and several others.

The author introduces a diagram of different water groups according to prof. A. A. Uklonsky. The diagram shows that the detailed Palmer’s classification has several omissions. The author suggests a more perfect numeration of waters, its substance clearly shown on fig. № 2. The essence of this numeration consists of giving the character of the chemical composition of water, sufficient for preliminary general considerations, with the assistance of one number, the so called water number. The water number is derived by means of simple reorganization, or diagrammatically from its chemical composition. By the water number one may calculate, with precision to 4% of reacting values, the sum of r. v. percentages of strong acids, weak acids, strong bases and weak bases. The water number allows to determine its appliance to one or the other group of waters by Palmer’s system. It will facilitate the solution of some genetic problems etc. Finally, the water number is an objective numeral standard determining the position of water in relation to its chemical properties among other natural waters of the globe.