CHEMICAL ANALYSES 



63 



molecular proportions or, as in samples 72 and 77, the 

 amount of potassium is greater than that of sodium. 

 The average composition of the clay mineral or 

 minerals in the samples, thus roughly corresponds to 

 the empirical formula: 



(Mg, K2, Na2, Ca)0 • 2(Al203, Fe203) • 6 Si02 



This is approximately the formula of beidellite, except 

 for the water, which has not been taken into account. The 



fact that the average silica sesquioxide ratio is some- 

 what less than 3 indicates that more or less kaolinite, 

 halloysite, or muscovite may be present. 



Besides the colloidal fractions of the five terrigenous 

 and pelagic clays, the clay and silt fractions of sample 

 17 and the colloidal separates of samples 19, 21, 23, and 

 81 were analyzed. In these five Globigerina oozes the 

 calciumcarbonatecontent is smaller in the colloidal parts 

 than in the whole samples, hence most of the other com- 

 ponents are larger in relative amount. It is interesting 



Table 12. Partial chemical analyses of fine fractions in per cent 



Abbreviations used as follows: n.d. = no determination, n.f. = none found, tr = trace. 



Analyses by Sharp-Schurtz Co., Lancaster, Ohio, except where indicated. Maximum size of particles 

 in fractions analyzed about 1 micron, except for sample 17. ^Duplicate determination on small sample 

 gave 2.71 per cent. ^Duplicate determination on small sample gave 9.07 per cent. ^ sample insuffi- 

 cient for determinations of Na20 or K2O. d Analysis by J. D. Loudermilk. ^ Analysis by titration 

 method; see table 26. f Analysis by Esther C. Allen and the writer. 



Table 13. Molecular ratios of fine fractions 



