supplemented by physical and chemical studies made by other methods; how- 

 ever, the method can also be used independently to great advantage in many 

 problems. At times X-ray diffraction methods are more rapid and efficient than 

 other methods and in some problems the answer can only be obtained by the 

 use of X-ray procedures. 



Due to their minute particle size, clay minerals are extremely difficult 

 to identify by other methods, especially so when they occur as mixtures. Figure 

 9-12 shows X-ray patterns of some of the more common clay minerals. It 

 should be observed that some members of the montmorillonite group show very 

 definite similarity; however, with the aid of a good set of standard patterns a 

 remarkable amount of information can be obtained from their diffraction 

 patterns. This information can be verified and extended appreciably by the use 

 of other methods such as differential-thermal analysis (Grim, 1942, 1947), 

 electron microscope studies and thermal gravimetric analysis (Mielenz, 1953). 

 The nature of the nominal 14^4 line (usually the first line in the pattern from 

 the center outward) gives considerable information about the adsorbed cations. 

 This can be verified with patterns from a series of specimens calcined at various 

 temperatures. Furthermore, patterns of mixed sodium and calcium adsorbed 

 cation clays made under controlled conditions enable us to determine the rela- 

 tive amounts of each of the ions present from the value of d spacing (Williams, 

 1953). Likewise the position of the nominal 1A9A line (060) (approximately 

 one half inch from edges of patterns in Figure 9-12) gives considerable informa- 

 tion concerning the nature of the ion in the octahedral position since the line 

 shifts toward the center of the pattern as the diameter of the ion increases. 



X-ray diffraction methods are likewise particularly valuable in the analyses 

 of shales. These are frequently so fine-grained and so heterogeneous in compo- 

 sition that alternative methods are inadequate. 



A brief description of a few of the many problems solved with X-ray 

 diffraction will serve to give the reader some idea of how X-ray diffraction 

 studies can be advantageously applied to problems that may be encountered in 

 various fields. 



Through X-ray diffraction studies it has been possible to learn the nature 

 of the structure of the various clay and micaceous minerals and the close struc- 

 tural relationship between them. Similar studies have given us a vast amount of 

 structural information for many other minerals. By means of X-ray diffraction 

 studies we were able to learn the nature of the mechanism of hydration in clay 

 minerals and some micaceous minerals which supplied us with information 

 concerning swelling behaviors and the development of excessive pressures with 

 moisture absorption by some types of dried clays when free swelling was 

 restricted. This now enables us to analyze the foundation materials upon which 

 structures, such as buildings, dams, and highways, are to be erected and thus 



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