From field observations and the study of the stone material at our disposal, it follows that in the magmatic process of formation of alkaline rocks of Tagoba-Sobak, three phases are established, replacing each other in the usual sequence: 1) the intrusive phase, represented by syenites, 2) vein - aplite and albitite, 3) phase of intensive manifestation of the process of pneumatolysis, completing magmatic activity. The last phase is associated with the formation of sodalite, cancrinite and other pegmatites and the automorphic change of rocks of early phases, expressed in intensive metasomatic replacement of primary minerals and leading to the formation of sodalite- and cancrinite- nepheline syenites. The change in the chemical composition of magma from early to late phases was expressed: 1) in the depletion of ferruginous-magnesian components: 2) in the enrichment of the magmatic melt with sodium and silicic acid and 3) in the concentration of mineralizers - F, CL, etc. By comparing the mineralogical composition of various xenoliths, on the one hand, and the mineralogical composition of xenoliths with that of typical biotite-nepheline syenites, on the other, one can be convinced that between the extreme member of the xenolith (vesuvian hybrid) and the biotite-nepheline syenite there is a connection and there are gradual transitions of one rock type to another (see article).
We studied random samples of thin sections of melted rocks, which were given to us by A.V. Vvedenskii. We did not pursue the goals of a systematic study of this random, although quite extensive (about 200 thin sections) material, and in this note we limited ourselves to only some data, characterizing the more common types of these "artificial rocks". The vast majority of the studied thin sections represent glasses that have just begun to crystallize with the formation of spherulites or various kinds of skeletal formations. Only in a few thin sections could one find individualized minerals in such a form that they were amenable to optical examination. Therefore, the main task of the study was the study of structures, and much less work was the study of minerals.
