SECT. 3] CLAY-MINERAL DISTRIBUTIONS IN THE PACIFIC OCEAN 729 



2. The Clay Minerals 



The clay minerals were identified by their X-ray basal reflections. Initially, 

 the samples were dispersed in distilled water and the soluble salts removed 

 through a filter cone by repeated washings. The <2 y. size fraction was 

 collected by centrifugation and the clays were pipetted on glass microscope 

 slides and air dried, and these oriented samples were then subjected to X-ray 

 diffraction analysis. 



A large number of the samples were preserved continuously under refrigera- 

 tion after removal from the sea floor and were in a moist condition. In certain 

 cases no moist samples were available and samples dried at room temperature 

 were used. To evaluate the effect of using such samples, controlled experiments 

 were conducted upon the moist materials. One portion was dried at 110°C 

 overnight and then rehydrated and the other left in its original wet condition. 

 The diffraction patterns of these two samples were identical within the limits of 

 error of the X-ray technique. 



A. Montmorillonites 



A diffraction peak that shifts to 17 A after ethylene glycol solvation was 

 assigned to the montmorillonite group (Bradley, 1945). This mineral could be a 

 true montmorillonite (low tetrahedral substitution) or an illite and/or chlorite 

 which has its inter-layer cations removed and now sorbs two layers of ethylene 

 glycol. This material would have a high tetrahedral charge. In some cases, and 

 maybe in all, it is possible to have a mixture of the two types either as discrete 

 mineral species or as intergrowths (Greene-Kelly, 1955; Jonas and Thomas, 

 1960). With glycol-glycerine sorption as the sole criterion, it is often difficult to 

 tell what phases are present (Johns and Tettenhorst, 1959). 



B. Illite 



Diffraction maxima at 10, 5 and 3.3 A which do not shift after ethylene 

 glycol solvation are characteristic of the illite group of clay minerals. In the 

 present investigation no attempt was made to distinguish 2M micas from the 

 IM and iMd tjrpes. 



C. Chlorite-Kaolinite 



Diffraction maxima at 7 and 3.5 A were attributed to the chlorite-kaolinite 

 groups. A distinct maximum at 14 or 4.7 A was used as evidence of chlorite. The 

 presence of kaolinite in those samples which contained chlorite could not be 

 determined with any degree of accuracy. Therefore in such cases the minerals 

 are reported as " chlorite -I- kaolinite " . 



D. H alloy site 



The electron-microscope pictures of the typical tubular morphology, coupled 

 with an electron diffraction pattern, uniquely determined halloysite. 



In order to show trends in the clay-mineral distribution, the ratio of the 



