NOTE ON THE FLUORINE CONTENT OF ROCKS AND OCEAN-BOTTOM SAMPLES 



Until recently little information has been available 

 concerning the amoimt of fluorine present in rocks, the 

 lack of data being due to the unreliable analytical meth- 

 ods in use. The WUlard and Winter procedure, pub- 

 lished in 1933 (1), furnishes an easy and surprisingly 

 accurate method of fluorine determination. Recent work 

 shows that instead of being a very minor constituent of 

 rocks, fluorine is present in about the same amount as 

 chlorine and must be considered in rock analyses. A 

 tentative average value of about 0.04 per cent is suggest- 

 ed and some indications point to regional concentrations. 

 Ocean-bottom samples are found to contain about the 

 same quantities as the rock. 



On the seventh cruise of the Carnegie ocean-bottom 

 samples were collected at many of the one himdred and 

 sixty-two oceanographic stations occupied. Representa- 

 tive samples were examined for fluorine content, with 

 the results shown in table 1. In the table the t3^e of bot- 

 tom material has been included. The fluorine content of 

 all the specimens averages 0.047 per cent. With the ex- 

 ception of no. 6, these are all from the Pacific Ocean. 

 The type of bottom evidently is important. Thus, globig- 

 erina ooze, being largely calcium carbonate, might be 

 expected to hold some excess of fluorine, but obviously 

 calcium fluoride is too soluble in sea water to permit 

 this. On the other hand, the aluminous clays retain 

 larger amounts. 



In figure 1 has been plotted geographically the fluo- 

 rine concentration of the ocean-bottom samples. The Station 

 fluorine concentration is proportional to the diameter of no. 

 the circles. With so few data one notes only trends, but 

 some of these are suggestive. It appears that there is a 

 notable concentration of fluorine between the west coast 

 of North America and the Hawaiian Islands. In view of 

 Zies's (2) observations on the great quantity of fluorine 

 given off by volcanoes in the Alaskan area, and assum- 

 ing that in the long continuance of Japanese volcanicity 

 similar amounts must have been evolved in that region, 

 we should expect the ocean bottom to have received 

 much of this fluorine and the samples to show a high 

 content all along this northern arc. Instead we find low, 

 or average, fluorine off the Japanese Islands and the 

 northern arc, and a notable concentration east of Hawaii. 

 It is possible that this concentration is related to the turn 

 of the ocean currents at this point, but no similar rich- 

 ness appears off the South American coast where some- 

 what similar conditions prevail. 



*The present note is an abstract of a paper entitled: 

 "Note on the fluorine content of rocks and ocean-bottom 

 samples," by E. S. Shepherd, of the Geophysical Labo- 

 ratory, Carnegie Institution of Washington, Washington, 

 D. C, published in the American Journal of Science, vol. 

 238, pages 117-128. 1940. 



LITERATURE 



One definite fact has been established by recent 

 studies of ocean-bottom samples and rock samples: flu- 

 orine is not an insignificant constituent of the earth's 

 crust, as had been supposed. It evidently is present in 

 quantities as great as, and sometimes greater than, 

 chlorine, and this poses a question for which at present 

 there is no satisfying answer. The question is: What 

 becomes of this fluorine? Zies has discussed this mat- 

 ter and summarized the answers thus far. It is true 

 that great deposits of fluorine as well as chlorine exist, 

 but it is far from clear how the fluorine that is being 

 released all over the earth finds its way into such de- 

 posits. The ocean-bottom data shed some light on this, 

 as do the few sedimentary rocks tested. Since 1933 

 much work has been and is being done on the fluorine 

 content of inland waters, and this work indicates again 

 the spotty character of such concentrations in various 

 geological formations. As this work continues we shall 

 be able to trace the vagaries of this elusive element. It 

 seems to the writer that when account is taken of all the 

 known loci of fluorine, there still remains a large amount 

 unaccounted for, or else the fluorine present in the outer 

 parts of the earth did not all derive from the rocks. 



Table 1. Ocean-bottom samples collected by 

 the Carnegie 



Type of sediment 



Fluorine 

 per cent 



1. Willard, H. H., and O. B. Winter. Volumetric method 

 for the determination of fluorine. Ind. Eng. Chem., 

 anal, ed., vol. 5, pp. 7-10. 1933. 



2. Zies, E. G. The valley of ten thousand smokes. 



Nation. Geog. Soc, Contrib. Tech. Papers, Katmai 

 series no. 4, 79 pp. 1929. 



85 



