52 



GENERAL DISCUSSION OF CLAYS. 



The following analyses indicate this fact : 



l 

 Per cent. 



Si0 2 47.20 



A1 2 O 3 36.50 



Fe 2 O 3 2.56 



CaO tr. 



MgO tr. 



Alkal'es 



H 2 13.35 



Moisture .50 



Total fluxes 2.56 



DEG. F. 

 Viscosity or fusion point. Above 2700 



1. Chalk Bluff, Marion Co., Ala., U. S. Geol. Surv. 18th Ann. Rep., Part V. 

 (continued), p. 1128. 



2. Fernbank, Lamar Co., Ala. Ibid. 



3. Norborne, Mo. Mo. Geol. Surv., XI. Ann. Rep. 



This is practically the full extent to which the ulti- 

 mate analysis can be used ; and t'here still remain 

 to be explained a number of physical facts concerning 

 any clay which happens to be under consideration. 



It frequently 'happens that two clays approach each 

 other quite closely in their ultimate composition, and 

 still exhibit an entirely different behavior when burn- 

 ed. The explanation which most quickly suggests it- 

 self is, that the elements present in the two clays are 

 differently combined. Some method of resolving the 

 clay into its mineral components, so as to indicate the 

 condition in which the elements are present is there- 

 fore practically needed. 



As kaolinite results from t'he decomposition of feld- 

 spar, the kaolin is quite sure to contain some unde- 

 composed feldspar, and also some quartz, and (in 

 smaller amounts) mica, since the two latter minerals 

 are common associates of the feldspar. 



If, now, we know the amount of feldspar, quartz 

 and kaolinite or clay-substance in the kaolin, and the 

 effect of these individual minerals, we can form a far 



