472 grim. CERAMICS AND CLAY COMPOSITION [Ch. 25 



properties, but it presents a rapid method of eliminating the worthless 

 materials. 



Although it is beyond the scope of this paper, it should be noted 

 that there is a correlation between the composition of clay materials 

 and uses of clay outside the field of ceramics, for example, in drilling 

 muds, decolorizing oils, fillers, etc. Determinations of composition, 

 therefore, also permit the selection of promising samples for com- 

 mercial use in fields other than ceramics. 



Evaluation of a Particular Clay Deposit 



A geologic study of a clay deposit involves two distinct problems: 

 first, the determination of the geologic setting; and, second, the uni- 

 formity of the properties of the clay in the deposit. The solution of 

 the first problem is straightforward geology; it provides data on the 

 size of the deposit, overburden, ground-water conditions, large varia- 

 tions in character, etc. 



The determination of uniformity of material in a clay body is apt 

 to be difficult, but it is of great importance. The commercial utiliza- 

 tion of a clay cannot be successful unless the deposit contains a large 

 amount of clay of highly uniform properties or capable of simple 

 beneficiation so that it can be made uniform. Any utilization of clay 

 is inherently based on certain properties that the clay possesses, so 

 that any change in the properties of the clay in a given deposit is likely 

 to cause great difficulty in its processing or use. American producers 

 of clay have not always realized the necessity of producing a uniform 

 product, and only after this was accomplished were they successful 

 in competing with clays that were imported into this country. 



Clay deposits seem to be inherently variable. A casual examination 

 may suggest that a clay body is uniform, whereas detailed tests will 

 reveal it to be quite variable. In other words, the outward appearance 

 of uniformity does not necessarily indicate uniformity in properties. 

 The fact that very small variations in composition may cause large 

 variations in properties must mean that important changes in physical 

 properties are often not accompanied by any changes in gross char- 

 acteristics. This is an exceedingly important point, and geologists and 

 others have been led into costly blunders because they assumed that 

 clay was inherently a relatively inert, uniform material that could be 

 evaluated by superficial study. Nothing could be further from the 

 truth. 



The detection of variations in properties involves the study of the 

 properties of many samples. Usually it is not enough to detect varia- 

 tions in properties; the cause of the variations, their relation to com- 



