SILICATES. 



SERPENTINE 



(Curve a, fig. 71.) 



The reflecting power of this mineral is low. The maxima are at 9.7 

 and 10.5 /A. 



COLEMANITE (Ca 2 B 8 Oii+5H 2 O). 

 (Cleavage piece parallel to b. Curve b, fig. 71.) 



From the transmission curve it will be noticed that this mineral is 

 very opaque. Yet it has no metallic reflection bands before arriving at 

 7 p. Its reflecting power of only i per cent at 4 /A is unusually low. 

 There are maxima at 7.3, 7.6 ( ?), 9.4, 10.6, and 11.2 p.. 



6 8 9 IO n /<? 



FIG. 71. Serpentine (a); Colemanite. 



AUJITE (NaAlSi 8 O 8 ). 

 (Curve a, fig. 72.) 



Section ground parallel to a cleavage plane. The curves of soda and 

 potash feldspars are unusually similar, as was found for transmission. 

 The maxima occur at 8.7, 9.7, and 10 /z. 



6 B 9 10 



FIG. 72. Albite (a) ; Orthoclase. 



I3ju. 



ORTHOCLASE (var. ADULARIA) (KAlSisOs). 

 (Curve b, fig. 72; cleavage parallel to c.~) 



The first maximum is shifted to 8.8 p., while the second is a broad 

 band, with a maximum at 9.8 p.. 



