CARBONATES. 



II 



Strontianite (SrC0 3 ). 

 (Massive specimen. From Hamm, Westphalia, Germany. Curve a, fig. 2.) 



The specimen examined had a large, well-polished reflecting surface. 

 As in all the carbonates studied the height of the maximum reflection is 

 only about 30 per cent. This is the only carbonate examined which has 

 but one reflection maximum, which is at 6.74//. It will be noticed pres- 

 ently that these maxima shift toward the long wave-lengths with increase 

 in molecular weight. Since the intensity of the two bands is unequal, it is 

 possible that this inequality, combined with the shift of the maxima, is the 

 cause of the lack of resolution. 



Witherite (BaC0 3 ). 

 (Massive, crystalline. Curve b, fig. 2.) 



The reflection decreases normally from 4 to 6/( followed by strong 

 complex reflection band, with maxima at 6.78 and 6.98 fi. The latter band 

 is the more intense, which is just the opposite of the carbonates, having a 

 metal of less molecular weight. The specimen had an unusually high 

 polish, which accounts, in part, for the high reflection maximum. 



Malachite (CuOCOvH 2 0). 

 (Concretionary specimen. From Burra Burra, South Australia. Curve a, fig. 3.) 



The specimen of malachite was highly polished. The reflection bands 

 are well resolved, while the second maximum is of the usual intensity for 

 carbonates. Beyond io/t there appears to be another band, but the un- 



20% 



4 5 6 7 8 9 



Fig. 3. Malachite (a); Azurite. 



steadiness of the galvanometer prevented an accurate determination of 

 this question. The maxima of malachite occur at 6.66 and 7.3 ,u, with a 

 possible third band at 7.8 \i. 



Azurite (3CUO2CO2H2O): Chrysocolla (CuSi0 3 +H 2 0). 

 (From Lyon County, Nevada. Curve b, fig. 3.) 



The specimen examined was a mixture of azurite and chrysocolla, the 

 first mineral being present in only a small amount. No silicate bands at 



