INFRA-RED TRANSMISSION SPECTRA. 



so prominent as a gas, is differently bonded in calcite and magnesite. 

 The same thing has been noticed in Azurite. 



MAGNESITE (MgCO 3 ). 

 (Massive; subtranslucent; / = o.op. Curve b, fig. 58.) 



This mineral is more unusual than calcite. It has the transparent 

 region of calcite, at 5 u, preceded and followed by almost complete 

 opacity. The bands at 3.3 and 3.8 /* are probably in common with 

 calcite. 



J 



!W\/U 



,5 6 7 8 3 IO II 



FIG. 58. Calcite (a); Magnesite. 



13 



CASSITERITE (SnO:). 

 (/ = 0.085 mm.; transparent. Curve a, fig. 17.) 



This section, when bought, was thought to be mellite; but its trans- 

 mission curve is so entirely different from what one would expect to 

 find for substances containing water of crystallization that it was sus- 

 pected to be another mineral. Specimens of mellite were purchased, 

 and found to be unusually opaque to heat rays. Upon inquiry from 

 the maker it was found that they had accidentally substituted cassiterite 

 for mellite. The fact that it was possible to detect the error would 

 indicate that the method of analysis is trustworthy. There are small 

 absorption bands at 1.3, 3, 5.8, 6.6, 7.3, 8.25, 9.7, and 10.4 p.. 



