736 



GRIFFIN AND GOLDBERG 



[CHAP. 26 



montmorillonite whereas they are distinctly different from true montmoril- 

 lonite. A true montmorillonite has its excess negative charge located in the 

 octahedral layer and little, if any, negative charge in the tetrahedral layer. The 

 micas, on the other hand, will have a high net negative charge in the tetrahedral 

 layer. Furthermore, the net charge on the montmorillonite will be much smaller 

 than that on the micas. 



So it would be expected that the stripped illite and chlorite would upon 

 entry into a proper environment revert back to better crystalline mica and 



Fig. 6. Concentration gradients of clay minerals in the North Pacific. 



chlorite by sorption and "fixation" of K+ and Mg2+. The phenomenon of K+ 

 "fixation" is well established and a voluminous literature on the subject has 

 been developed by soil scientists (Volk, 1938; Barshad, 1954). Recently, Weaver 

 (1958) used the phenomenon to differentiate montmorillonite from stripped 

 micas. He showed that the montmorillonite would not "fix" K+ and then 

 collapse, whereas stripped micas would readily "fix" K+ and collajjse. 



An examination of the 17 A peak from diffraction tracings taken from the 

 surface sediment in the east to west traverse across the North Pacific lends 

 support to the hypothesis that the 17 A material is sorbing K+ and Mg2+ and 

 collapsing. In nearshore sediments the 17 A peak is sharp. However, further 

 from land, the peak broadens and loses intensity because of random inter- 

 layer collapse. In the mid-oceanic areas the peaks disappear (Fig. 7). 



At first glance this striking correlation of the 17 A peak broadening and 



