i8 



INFRA-RED REFLECTION SPECTRA. 



ALUMINUM SILICATES. 

 There is no special reason for thus classifying the following minerals, 

 except that most of them are quite unlike the commoner silicates previously 



examined. 



Cyanite (Al 2 3 Si0 2 ). 



(Yancy County, North Carolina. Curve a, fig. 10.) 



The color of this flat crystal was light green. The flat crystal face, 

 2 -5 by 3.5 cm., was ground but did not have a high polish. The band of 

 selective reflection has three sharp maxima, at 9.3, 9.78, and 10.28^, 



6 7 8 9 10 II 



Fig. 10. Cyanite (a); Corundum. 



12 



13 



14 



15/1 



respectively, and is not unlike that of willemite (Zn 2 Si0 4 ), except that in 

 the latter the whole band is shifted to longer wave-lengths with the maxima 

 at 10. 1, 10.6, and 11 ;t. 



Beryl [BejAhKSiOa)*]. 

 (From North Carolina. Fig. n.) 



The surface examined was ground on a crystal face. The specimen 

 was opaque and green in color. The reflection curve follows the usual 

 course with a band of selective reflection extending from 8 to 10.5 [x. The 



50% 



40 



c 

 .2 30 



< 20 



10 



ifc-s 



10 



'2 



I3JJ. 



Fig. 11. Beryl. 



maxima are not so high as usual with silicates, but they are sharp and 

 occur at 8.15, 9.2, 9.9, and 10.4/*. 



