CARBONATES. 



23 



80% 



70 



60 



50 



<J 



_0j40 





cleavage face of Iceland spar. With the larger dispersion the band pre- 

 viously found at 6.6 jj. is now resolved into two bands with maxima at 

 6.5 and 6.6 /, respectively. The 

 region at 7 / is evidently still 

 more complex, but not resolved 

 even with this greater dispersion. 

 In curve b is given the reflection 

 spectrum of a clear crystal of 

 aragonite. The crystal face was 

 small, only about 6 by 15 mm., 

 and since the area of the com- 

 parison mirror was not reduced 

 in like proportion, the reflecting 

 power of the maxima is really 

 higher than here given. In fact, 

 for a well-polished crystal the 

 reflecting power is no doubt as 

 high as for calcite. The impor- 

 tant point of interest in the pres- 

 ent examination is that aragonite has only two reflection maxima, of about 

 equal intensity, and located at 6.53 and 6.75 /, respectively. 



Magnesite (MgC0 3 ). 

 (Curve a, fig. 16.) 



This sample was previously examined (fig. 5). In the present curve 

 there are three bands with maxima at 6.42, 6.65, and 6.9 p.. 



60%r 



30 



20 



10 



6.0 



.2 



.3 



1.0 



A .6 



Fig. 15. Calcite (a); Aragonite. 



.2 



7.4// 



50 



40 



c 

 o 



13 30 



ce 



20 



10 



0.2 .4 .0 .a 7 .2 



Fig. 16. Magnesite (a); Smithsonite. 



7.4/i 



Smithsonite (ZnC0 3 ). 

 (Curve b, fig. 16.) 



This sample was previously examined (fig. 1), when two maxima were 

 found. In the present examination the bands are more resolved, but the 

 maxima occur at 6.65 and 7.05^, respectively, as in the previous investigation. 



