SOBOLEV 366 



find basic syenites and new deposits of piezo-electric crystals 

 in this region of the Ukraine. 



In post-war years, Sobolev has devoted much of his time to 

 the study of young volcanic rocks in the Carpathian Mountains. 

 Explorations in this region are being conducted jointly with a 

 group of his students. In his writings on the mineralogy and 

 petrology of the Ukrainian S.S.R. he described the ultra- 

 basic rocks of Transcarpathia and established, within the meta- 

 morphic complex of this region, the occurrence of diaphtoresis; 

 he has described a new find of pumpellyite from the Carpathian 

 Mountains, pointing out the identity of this mineral to lotrite 

 and others. 



Sobolev is not only a petrographer but a mineralogist as 

 well. He has published since 1944 a series of articles on the 

 theoretical mineralogy of silicates, and in 1949 a book entitled 

 Introduction to the Mineralogy of Silicates which was awarded a 

 Stalin Prize, Second Class. In this treatise he attempted to 

 make an interrelationship between the properties and genesis 

 of minerals, on the one hand, and silicates and their crystal 

 structure on the other. He has established a connection between 

 the difference in ionic radii in isomorphic series and the type 

 of fusibility curves; substantiated A. E. Fersman's ideas re- 

 specting the regularity of isomorphism; determined the re- 

 lationship between the change in the coordinate number of alumi- 

 num during mineral formation and the physico-chemical 

 equilibrium factors; clarified the relationship between the opti- 

 cal properties of silicates, including their color, and their 

 structure. Moreover, he has generalized the data of paragene- 

 sis of igneous rocks in the form of multi -fascicular diagrams. 



Certain structural features of various silicates, which had 

 been predicted by V. S. Sobolev on the basis of mechanisms 

 which he had evolved, have been verified by X-ray analysis. 

 Thus, for example, the investigations conducted by N. V. Belov 

 and I. M. Rumanova have corroborated his hypothesis concern- 

 ing both the six-fold coordination of aluminum in epidote and 

 the presence of a diortho group in the latter. Studies by 

 Chinese authors have supported his hypothesis concerning the 

 two types of coordination of aluminum in prehnite and others, 

 ite and others. 



Maintaining in his studies that hydroxyl in many silicates 

 cannot substitute oxygen in oxysilicic tetrahedrons, V. S. Sobo- 

 lev proposed in this connection a new way of computing the 

 crystallo- chemical formulas of water -containing silicates. In 

 1949, he was the first to advance the hypothesis concerning the 



