144 wherry: neodymium, cause of red-violet color 



lenl process fusing with alkalies and then acidifying— in the 

 course of which the minerals would be destroyed; moreover 

 they are extremely unstable, and even if formed could hardly 

 persist long. Finally, permanganates show a highly character- 

 istic absorption spectrum — observable by placing their solutions 

 between a source of white light and the slit of a spectroscope — 

 consisting of six bands in the yellowish green, green, and green- 

 ish blue; but not a trace of this absorption spectrum is shown 

 by any mineral thus far studied. 



Certain manganic compounds, containing trivalent manganese, 

 are, however, also red- violet in color, and may develop in min- 

 erals under mildly oxidizing conditions. Even colorless bottle- 

 glass, on lying out in the sunlight for a time, becomes red-violet 

 owing to the oxidation of the manganese to that valency. 2 Such 

 manganic compounds show a single rather hazy absorption band 

 in the greenish blue, but only indistinct general absorption of the 

 colors complementary to red-violet. 



On the other hand, there is at least one other chemical ele- 

 ment, the rare-earth metal neodymium, which has red-violet or 

 violet-red colored compounds; and these yield a highly charac- 

 teristic absorption spectrum, consisting of an intense band in the 

 orange-yellow, a fainter one in the green, and, if sufficiently 

 concentrated, additional ones in other parts of the spectrum. 

 These bands can readily be seen if a solution of monazite in 

 sulfuric acid is placed between the source of light and the spec- 

 troscope slit. They can also be observed in a number of min- 

 erals, by the use of the microspectroscope. 3 Of course if the 

 mineral occurs in large enough masses, the ordinary spectroscope 

 may be used, and the mineral be simply placed between the 

 source of light and the slit; those described in this note give 

 good results by this method. 



It was pointed out by Headden some years ago 4 that the 



2 See Gortner, R. A. Journ. Amer. Chem. Soc, 39: 157-162, 1908. 



3 See the writer's paper, The microspectroscope in mineralogy, Smithsonian 

 Misc. Coll., 65, No. 5, 1915. 



* Am. J. Sci., [4] 21: 301, 1906. 



