NO. 5 THE MICROSPECTROSCOPE IN MINERALOGY WHERRY 3 



of the absorption spectra of the different minerals for determinative 

 purposes, this degree of accuracy is quite sufficient. 



The light diffused by mineral grains shows in most cases more 

 intense absorption bands than that transmitted directly through them, 

 yet it must penetrate considerably to be affected at all, so that only 

 transparent or fairly translucent minerals yield any effects; in 

 addition they must be more or less distinctly colored. The number 

 of minerals suitable for microspectroscopic study is therefore rather 

 limited, but the fact that the specimens need not be scratched, broken, 



Fig. i. — The wave length scale of the Abbe-Zeiss microspectro- 

 scope, with the absorption spectrum of " didymium " glass, the 

 interval between the two strongest bands of which is set at 058. 

 The several bands lie at 067.5, 062.5, 059-0, 058.2, 057.4, 053.1, 052.5, 

 051.2, 048.0, 044.8, and 043.3. Transmitted light; source, Welsbach 

 burner ; exposure 1 hour ; Wratten and Wainwright Panchromatic 

 plate. 



or altered in any way renders the method of considerable use in the 

 identification of crystals too valuable to be broken up for the usual 

 tests, and in particular of cut gems, whether free or in their settings. 

 Even where other methods are applicable the spectra may serve as 

 confirmatory tests. 



This method has proved especially useful in determining the 

 genuineness of rubies, sapphires, and emeralds sent to the Museum 

 for examination and report, in picking out corundum, zircon, and 



