Chapter 25 



APPLICATION OF STUDIES OF THE COMPOSITION OF 

 CLAYS IN THE FIELD OF CERAMICS * 



Ralph E. Grim 



Geologist, Illinois State Geological Survey 

 Urbana, Illinois 



This chapter states briefly the factors of composition which deter- 

 mine the properties of clays and discusses the relation of the factors 

 of composition to the particular properties of clays which determine 

 their use for ceramic purposes. The practical application of studies 

 of the composition of clays, particularly in the field of ceramics, is 

 also discussed. 



THE COMPOSITION OF CLAY MATERIALS 



It is generally agreed by present-day students of clays that clay 

 materials are composed essentially of crystalline particles of members 

 of any one or more of a few groups of minerals known as the clay 

 minerals (Grim, 1942). The clay minerals are hydrous aluminum 

 silicates, frequently with some replacement of the aluminum by iron 

 and magnesium and with small amounts of alkalies and alkali-earths. 

 In some clay minerals, magnesium and iron completely replace alumi- 

 num. In addition to the clay minerals, variable amounts of quartz, 

 limonitic material, feldspar, pyrite, organic material, and a host of 

 other minerals may be present as extremely minor constituents, or as 

 prominent constituents in some clays. Most of the clay minerals occur 

 in flat, flake-shaped particles. The unit shape of some clay minerals 

 is lath- or fiber-shaped. The clay minerals occur in most clay mate- 

 rials in particles less than about 0.005 millimeter in diameter. Table 

 1 lists the common clay mineral groups together with their composi- 

 tion. 



* Published with the permission of the Chief, Illinois State Geological Survey. 



464 



