J. B. Ferguson — Molybdenum in Rocks. 399 



Akt. XXXII. — The Occurrence of Molybdenum in Rocks 

 with special reference to those of Hawaii / by J. B. 

 Ferguson. 



Some years ago, Dr. W. F. Hillebrand,* by a long series of 

 determinations, showed that vanadium was most abundant in 

 the less siliceous rocks, such as basalts, gabbros and diorites ; 

 while molybdenum seemed to be confined entirely to the more 

 highly siliceous ones, the granites and rhyolites, not a trace of 

 this element being found by him in the less siliceous rocks. 

 It was, therefore, a matter of great surprise to find decidedly 

 strong traces of molybdenumf in two basaltic lavas of Kilauea 

 which were analyzed by me for Day and Shepherd. These 

 analyses have been published in full 4 



On going over the list of rocks in which molybdenum was 

 searched for by Hillebrand, it was noted that he had tested 

 for it only in the more calcic and less sodic basalts and other 

 less siliceous rocks, and that by some chance not a single test 

 for this element had been made by him in nephelite-basanites 

 and other distinctly sodic rocks in which he had looked for 

 vanadium. As it is well-known that some of the rare elements 

 are often found associated with one or other of the more com- 

 mon ones, zirconium with sodium, for example, or chromium 

 with magnesium, § it seemed possible that this might also be 

 true of molybdenum, and that its presence in the basalts might 

 have some connection with the decidedly sodic character of the 

 Kilauean lavas. I therefore undertook the examination of 

 some sodic, and especially nephelite-bearing igneous rocks. 

 Dr. H. S. Washington kindly placed at my disposal a sufficient 

 supply of the original material which had served for his 

 analyses of several such rocks, together with a sample of 

 a leucite trachyte exceptionally high in potash, on the chance 

 that molybdenum might be found associated with this element. 

 Dr. Hillebrand also was kind enough to provide me with some 

 of the original material used by him for the analysis of a 

 Hawaiian trachyte-obsidian described by Cross. As a matter 

 of convenience, the complete analyses are collected in the fol- 

 lowing table : 



* Hillebrand, W. F., Distribution and quantitative occurrence of vanadium 

 and molybdenum in rocks in the United States. This Journal (4), vi, 209, 

 1896 ; Chem. News, lxxviii, 216, 1898 ; Bull. IT. S. Geol. Survey, No. 167, 

 p. 49, 1900. 



f Dr. Hillebrand was kind enough to look at the blue coloration indicating 

 molybdenum found by me, and to confirm my opinion that it was 

 molybdenum. 



JDay and Shepherd, Water and volcanic activity, Bull. Geol. Soc. Amer., 

 xxiv, 573-606, pi. 17-27. 1913. 



§ Washington , H. S., The distribution of the elements in igneous rocks, 

 Trans. Am. Inst. Min. Eng.. 1908, pp. 735. 



Am. Jottr. Sci.— Fourth Series, Vol. XXXVII, No. 221.— May, 1914. 



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