680 ARRHENIUS [CHAP. 25 



by crystallization of less soluble solids; barium, strontium, and lead separate 

 into harmotome-type zeolites, manganese oxide minerals, possibly including 

 psilomelane, and further crystalline solid solutions of celestite, barite, and angle- 

 site in proportions mentioned above. At slight solution of the celestobarite in 

 distilled water, the crystal faces develop a typical pitted appearance (Fig. 13, 

 A-H). The lack of these etching features in the crystals as found in the sediment 

 (Fig. 13, I-J) indicates that dissolution of celestobarite is not taking place on 

 the ocean floor. 



Besides the extensive cation substitution in the celestobarite crystals, re- 

 placement of SO4 by BF4 and possibly Cr04 is indicated by the presence of 

 1000 ppm of boron and 1400 ppm of chromium in this mineral. These and the 

 cation substitutions are of potential interest as indicators of the physico- 

 chemical conditions in the sea-water and in the interstitial solution. 



The exceedingly slow crystal growth on the ocean floor probably produces a 

 close approach to thermodynamic equilibrium between the liquid and the solid 

 solution. If in the relation 



Be and Ac denote the concentrations of the substituting species and the sub- 

 stituted main species respectively in the crystal, and Bi and Ai the corres- 

 ponding concentrations in the liquid, the partition coefficient, D, indicates the 

 enrichment (if > 1) or depletion of the substituting foreign ion in the crystal 

 structure. If Be and Ac are known from analysis of the actual crystals, and D 

 from controlled experiments, the ionic ratio, BjA, in the bottom water or inter- 

 stitial solution from which the crystals formed can be derived. For the cation 

 substitution couple, Sr2+/Ba2+, the ionic ratio in the halmeic crystals is 0.057, 

 and D has been determined to be 0.030 ± 0.004 (Gordon, Reimer and Burtt, 

 1954). The solution in equilibrium with these crystals should consequently 

 have an ionic ratio, Sr2+/Ba2+, of 1.9. If 114xl0~3 mmole/1. (the average 

 strontium concentration in sea-water) is accepted as a minimum concentration 

 value in the interstitial solution of the sediment, then a minimum concentra- 

 tion of 60 X 10~3 mmole/1. of barium is needed to maintain the ratio indicated 

 by the crystal composition. Such a barium concentration would be 136 times 

 higher than that observed in deep water. A part of this apparent discrejDancy 

 might be due to lowering of the strontium concentration in the interstitial 

 water by the zeolite and oxide species observed in co -existence with the barite; 

 however, a considerably higher barium concentration in the interstitial water 

 than in the deep water is suggested by these data. Chow and Goldberg {op. 

 cit.) have interpreted the deep-water concentrations observed by them as close 

 to saturation with the sedimentary barite. However, considerably higher 

 saturation concentrations should be expected since both the cation and the 

 anion substitution in the barite structure contribute to a markedly increased 

 solubility of the crystalline solid solution above that of pure barite. In pure 



