schaller: ilsemannite 419 



Tests made on ilsemannite from other localities show that 

 iron sulphate is present in all specimens examined, and if, there- 

 fore, the figures for melanterite are deducted from the ratios 

 given above, the remainder gives the ratio of Mo0 3 : S0 3 : H 2 

 as 1:1:5. It is suggested, therefore, that the formula of ilse- 

 mannite be taken as Mo0 3 .S0 3 .5H 2 until further quantitative 

 analysis, on pure material, shows a difference. The analysis of 

 the deep-blue mine 'water from Idaho Springs, Colo., approxi- 

 mates closely, after deducting for other sulphates, to a ratio of 

 1 : 1 for Mo0 3 : S0 3 , and this mine water is probably a solution 

 of ilsemannite. A sulphate of molybdenum, Mo0 3 .S0 3 , has been 

 prepared artificially. 



A specimen from Saxony showed abundant ilsemannite mixed 

 with iron sulphate, and selected portions of the blue mineral 

 gave a strong sulphate reaction and showed only a small amount 

 of iron. Another specimen from Carinthia gave a strong sul- 

 phate reaction with no ferrous iron and only a trace of ferric iron. 

 These two specimens were kindly loaned by Col. Washington 

 A. Roebling, of Trenton, N. J. The ilsemannite from Cripple 

 Creek, Colo., described by Lindgren and Ransome 3 gives like- 

 wise a strong sulphate reaction. It is suggested that what is 

 called a new molybdenum mineral by Horton 4 is either a yellow 

 sulphate of iron or yellow molybdite impregnated with a blue 

 solution of ilsemannite, the combination of the blue and yellow 

 producing green. Such a green coating was observed on the 

 specimen from Cripple Creek, Colo. 



The origin of ilsemannite should be studied in detail for each 

 occurrence, but the following suggestions may be offered: 



1. Oxidation of molybdenite: MoS 2 + 9 + 6H 2 = Mo0 3 . 

 S0 3 .5H 2 + H 2 S0 4 . 



2. Oxidation of jordisite, 5 the colloidal form of molybdenite, 

 the powdery character of jordisite allowing of more ready oxida- 

 tion and alteration. 



3 Lindgren, W., and Ransome, F. L. Geology and gold deposits of the Cripple 

 Creek district, Colorado. U. S. Geol. Survey Prof. Paper 54, p. 124. 1906. 



4 Hoktox, F. W. Op. cit., p. 15. 



5 Cornu, F. Zeitschr. Chem. Indust. Kolloide, 4: 190. 1909. 



