From year to year the sphere of application of X-Rays to the solution of both theoretical and practical problems becomes wider and wider. Thus the X-Rays are now applied for the purpose of identification of crystalline substances. The unequaled excellence of the X-Ray method is particularly manifest in geology and mineralogy. For a long series of minerals of vase industrial importance, as iron, nickel, manganese, and copper ores, clay and cement minerals, fine fractions of rocks, ochrous Mo-, Sb-, As-, W-minerals, etc. all other methods of investigation (chemical, optical, mechanical, etc.)' because of the pulverulent character of the objects, can give no positive results or meet with great difficulties in their application. In these cases the X-Ray method is the only efficacious method of investigation. It proves also to be the only method to apply in determining such and such peculiarities or changes in the crystalline structure of the substances under consideration. In the study of isomorphic groups of minerals this method renders unique services in clearing up the characteristic peculiarities of isomorphic replacement and changes in crystalline structures which are connected therewith. In every investigation of crystalline substances the X-Ray method must be applied side by side with all other methods of investigation, because it gives the possibility of ascertaining the most important, perhaps, of all the constants of a crystalline substance, namely the dimensions of the elementary cell and the scheme of the position, of atoms or ions in the structure. The X-Ray method of investigation acquires greater and greater authority with chemists, mineralogists and miners. Yet a wide application of this method for the purpose of identification of crystalline substances has been till now greatly hindered by the absence of more or less comprehensive X-Ray determinative tables adopted to the purpose of X-Ray mineralogical diagnostics. Disconnected works on separate minerals, or groups of them, scattered in literature though containing some X-Ray data, did but little to eliminate this defect, because, first, they were not adopted to the purpose of identification, and, secondly, they concerned a comparatively small number of minerals. In later works of 1935 and 1936 some authors try to adopt X-Ray data to the purpose of identification, but in these works the problem of producing any X-Ray determinative tables is solved only under a particular form, for a separate group of minerals studies by the authors. The present work constitutes the second issue of the X-ray determinator.

The aim of the present work which was begun after a similar work of V. Michelev (1) was to obtain the standard x-ray powder diffraction patterns of minerals and to determine the mineralogical composition of melted rocks by means of x-ray examination. The methods of optical determination of the mineralogical composition of the melted rocks are not always satisfactory, and therefore the x-ray examination is for the present time a irreplaceable. The x-ray powder method may be applied for the determination of the mineralogical composition of a casting and x-raying is to used to disclose their defects. In order to identify the x-ray diffraction patterns of melted rocks with known minerals we had to obtain as many films of these minerals as possible. By means of the x-ray powder method we have received the diffraction patterns of the following minerals: almandine (Fe₃Al₂Si₃O₁₂), grossular (Ca₃Al₂Si₃O₁₂), actinolite H₃Ca₈(Mg, Fe)₅(SiO₃)₈, hornblende (OH, F)₂ (Na, Ca, K, Mn)₂₋₃ (Mg, Fe, Ti, Mn, Al)₅ (Si, Al)₆O₂₂, synthetic spinel (MgAl₂O₄) and two of melted rocks. In order to avoid some experimental errors in the investigation of minerals it was necessary to have the diffraction patterns of pure specimens and those of specimens with admixture of rock salt (NaCl).

By means of the (Debay-Scherrer-Hull) powder method have been investigated fourteen minerals of the class of oxides. In the present paper are given exact values of the interplanar distances and relative intensities of lines, for the following minerals: thorite, cassiterite, polyanite, ilmenorutile, wood-tin, pyrolysite, thorianite, uraninite, nasturan, senarmonitite, arsenolite, claudetite and Sb-ocher. The tables given in this paper may be considered as material for "Röntgenometrical Determinative Tables of Minerals". Besides, there are also given models of tables and methodology of preparation of powder diagrams which will be useful in the future work as example on the composition of "Röntgenometrical Determinative Tables of Minerals".

At the beginning of this century, E. S. Fedorov created a method for determining a substance by the shape of its crystals, which he called “Crystal-chemical analysis” (29). This method, based on measuring the angles between the outer faces of crystals, was an important fundamental and practical achievement of crystallography. Over the next few years, this method, which in its essence is best called goniometric diagnosis, was significantly simplified by Fedorov’s school. Currently, the Fedorov Institute and the Central Geological Prospecting Institute (TsNIGRI) are compiling a “Crystal Determinant” (2), which will enable goniometric diagnosis in its new version to enter, along with optical diagnosis, into the daily practice of a crystallographer, chemist, and mineralogist. The main advantages of goniometric diagnosis are the complete absence of substance consumption, comparative speed of determination and the same degree of simplicity of diagnosis both in the case of simple and in the case of extremely complex substances. The main disadvantages of the goniometric method are the need to have the substance in the form of crystals and the variability of the external shape of crystals of the same substance. The second drawback may in some cases make it impossible to determine the substance by goniometric method. This drawback is especially noticeable in Barker’s version (16) of the goniometric diagnosis (20, 328, 329), to a somewhat lesser extent in Fedorov’s “Crystallochemical Analysis” and to an even lesser extent in the version embodied in the “Identifier of Crystals” mentioned above.