For many years (1930-1950) it was believed that within the crystal-bearing provinces quartz veins and nests with quartz crystals are placed sporadically and, as a rule, singly. Therefore, the reserves of piezo-optical raw materials were not calculated, and exploration and mining works were of ineffective seasonal character.

All textbooks on the geology of mineral deposits provide only the geological and economic definition of a mineral deposit. This definition is usually formulated as follows: a mineral deposit is an area of the Earth's crust with a characteristic geological structure in which the mineral is concentrated in quantities sufficient for exploitation, and its quality meets the requirements of industry. This definition is correct, but it does not clearly reflect the economic side of the problem. The fact is that it is not always economically feasible to develop even such a deposit, in which the mineral is concentrated both in quantity and quality sufficient for exploitation. For example, chromite deposits in the Polar Urals are characterized by ores of high quality (magnoochromite metallurgical ores) and contain ore in quantities sufficient for exploitation. However, the development of these deposits is currently not economically feasible for the following main reasons: the nearest railroad station is 250 km away from the area of the deposits; carrying out a railroad or highway is associated with great difficulties due to swamps, sharply dissected relief and permafrost; there are no consumers of chromite ore in the Komi ASSR. Consequently, at present the chromite deposits of the Polar Urals cannot be considered industrial, although the ore here is of high quality and the quantity is sufficient for exploitation ...

Crustalization of quartz veins. Three systems of tectonic fractures dominate in the rocks of the crystal province of the Subpolar Urals: consonant, secant and transverse fractures. Almost all crystal quartz veins of the studied area are confined to these fractures.

Most researchers of rock crystal deposits, the Subpolar Urals believe that the components that make up the nest minerals are carried by hydrothermal solutions from the magmatic hearth. Let us see to what extent this widespread opinion is confirmed by the actual material during a more or less detailed study of the composition of the host rocks and crystal nests.The striking similarity of the bulk chemical composition of the minerals of the crystal nests and the host rocks is striking even at a cursory acquaintance with chemical analyses. Chemical analyses show that the minerals of crystal nests of the circumpolar Urals consist of the following components: SiO2, Al2O3, FeO, MgO, CaO, Na2O, K2O, Fe2O3, TiO2, MnO, H2O и CO2. All these components are also included in the rocks hosting the crystal nests. Characteristically, the quantitative ratios between the above components are almost identical both in the total composition of the nesting minerals and in the rocks hosting the crystal nests.

The magmatic origin of the solutions from which the crystal-bearing quartz veins of the studied region were formed is recognized by most researchers. Of all the questions related to the genesis of crystal-bearing quartz veins, the main and decisive one is the question of the source of the substance and especially the source of silica in the hydrothermal solutions from which these deposits were formed. But it is precisely on this issue that there are the greatest and most fundamental disagreements between researchers of rock crystal deposits not only in the studied region, but throughout the world. Some researchers consider the magmatic chamber to be the main source of the substance in hydrothermal solutions, while others believe the host rocks. Since this dispute is based mainly on hypothetical reasoning rather than direct observations and data, this issue remains controversial to this day. Moreover, the dispute between researchers of rock crystal deposits has taken on such a long-lasting nature, apparently also because none of the researchers has attempted to approach the solution of this problem, dividing it into two components: the source of silica in quartz veins and the source of the substance, including silica in crystal nests. In this regard, the convincing arguments of the supporters of one theory were shattered by the no less convincing arguments of the supporters of opposing views. The correct solution to the question of the source of silica, and all other components of crystal-bearing quartz veins, is not a purely academic dispute, but undoubtedly has great practical significance.

Even a cursory review of the geological map of the Crystal Belt of the Subpolar Urals leads to the conclusion that numerous deposits of piezo-optical quartz are localized in the metamorphic strata of the Proterozoic and Lower Silurian, and in the northeast are quite clearly delineated by outcrops of the third formation. It should be noted that the lower formation is composed predominantly of mica schists, the middle - of quartzites, and the upper - of limestones. Consequently, the partitioning of the metamorphic strata of the Subpolar Urals characterizes not only the relative age of the formations, but also the peculiarities of the chemical composition of the rocks. Therefore, within the crustal band stratigraphic search features are inseparably connected with lithologic ones. In addition, the dependence of the mineral composition of crystal nests on the chemistry of the host rocks is quite definitely outlined even on a regional scale: essentially quartz rocks - Proterozoic shales and quartzites of the Lower Silurian are saturated with nests with quartz crystals, while limestones of the Upper Formation do not contain crystal vaults.

The crystal-bearing strip of the Subpolar Urals, the geological description of which is the subject of this article, covers the watershed part of the Ural Range, located within 64°30' - 65°20' north latitude, i.e. from Mount Khus-Oika in the south to the Maldy Range in the north. Along the main watershed of the Ural Range, the crystal-bearing strip has been traced for 150 km and is 25 km wide. The geological study of the crystal-bearing strip is being carried out by the Polar-Ural Expedition of the 8th Main Directorate of the USSR Ministry of the Pacific Ocean. The author of the article took part in the work of this expedition for 10 years. In 1952, the author, together with geologist V. A. Smirnova, completed the compilation of a geological map of the crystal-bearing strip on a scale of 1:100,000 for an area of ​​about 4000 km2. Unfortunately, this map cannot be included as a necessary supplement to this article due to its large size.

Three systems of jointing cracks predominate in the rocks of the crystal-bearing strip of the Northern Urals: concordant, intersecting and transverse. Almost all crystal-bearing quartz veins of the Northern Urals are confined to these cracks. Among the quartz veins of the Northern Urals, the first two types are most common. Transverse quartz veins are less common. It should be noted that the division of quartz veins into the listed types is conditional, since they are all of the same age, genetically related and fulfill a system of three interconnected tectonic cracks

In the early stages of studying the piezo-optical quartz deposits of the Northern Urals, some geologists believed that crystal nests had no genetic connection with quartz veins. Geologists came to this conclusion because at that time the bulk of piezo-optical quartz was mined not from crystal nests, but from placers, and geologists did not have enough data to correctly resolve this issue. Later, in connection with the transition to exploration of primary deposits, it was established that in most cases quartz veins and crystal nests are located in the same cracks. The asymmetrical arrangement of crystal nests in relation to quartz veins does not give reason to deny the genetic relationship of both, but only indicates a later formation of crystal nests compared to quartz veins. In all likelihood, after the formation of quartz veins, there was a fairly long intermineralization break, after which crack formation and the flow of hydrothermal solutions resumed. The duration of the intermineralization break can be judged by the sharp change in the nature of the hydrothermal solutions - from highly supersaturated with silicic acid (during the formation of quartz veins) to normal (during the formation of quartz crystals). Consequently, quartz veins and crystal nests are derivatives of a single magmatic chamber, but they were only formed in different phases of a single hydrothermal process.