NO. 5 THE MICROSPECTROSCOPE IN MINERALOGY WHERRY 5 



of the same crystals fail to show the slightest trace of them. Violet 

 calcite from another locality, Rossie, New York, also shows these 

 bands faintly. 



On heating the violet calcite in an air bath to about 400 for ten 

 minutes the color is completely discharged (yellow light being 

 emitted) and the absorption bands disappear. The simplest expla- 

 nation of this behavior is that the rare earths are originally present 

 as carbonates (in solid solution of the mix-crystal type), and in that 

 form show the absorption bands, but that, on heating, these com- 

 pounds are converted into oxides, which do not show them. Head- 

 den's observation that the yellow calcite from Joplin contains more 

 rare earths than other varieties can be readily reconciled with the 

 absence of bands in its spectrum by recognizing that the metals may 

 be present in it only as oxides in the first place. 



It is therefore concluded that violet calcite probably owes its color 

 to the presence, in mix-crystal form, of traces of a carbonate of 

 neodymium. 



Yellow titanite labeled as from " Mont Blanc " and brown apatite 

 from several places in Ontario, Canada, show the neodymium bands 

 with about the same intensity as the violet calcite, although the 

 violet color is hidden by stronger ones due to iron or other con- 

 stituents. The remainder of the minerals listed in the rare earth 

 tables are well known compounds of those elements. 



URANIUM MINERALS 



Transparent minerals containing uranium in the uranic form show 

 an absorption spectrum consisting of several bands in the green, 

 blue, and violet, viewing the grains at an angle to the path of the 

 light giving the most brilliant effects. The variation in the posi- 

 tions and relative intensities of these bands from one species to 

 another is particularly well marked and of some diagnostic value, 

 although more than 30 per cent of uranium must be present, and 

 many minerals with even this amount yield no spectra. 



Some specimens of the mineral zircon yield, as has long been 

 known, a number of absorption bands, which correspond to those 

 shown by uranium salts after reduction with zinc, that is, when in 

 the uranous condition. This uranium, which is present in minute 

 amount, mostly less than 0.5 per cent, has the same valence as the 

 zirconium and no doubt replaces a part of it, giving a blue color to 

 the mineral, which may, however, be hidden by other tints, due to 

 iron, manganese, etc. It therefore cannot be predicted whether a 

 given crystal of zircon will show a spectrum or not, but, on the other 



