SILICATES. 



DATOLITE (Ca(BOH)SiO). 

 (Curve a, fig. 74.) 



The reflection curve shows a series of small, sharp maxima at 8.8, 

 9.2, 9.5, 10, and 10.8 p. The reflection was from a natural crystal face. 



HYDROTALCITE (Mg 3 Al(OH),+3H I O). 

 (Curve b, fig. 74.) 



The results from this mineral are rather disappointing. There is but 

 one reflection maximum at 9.9 /*, and this one is not very large. The 

 transmission curve shows great opacity. 



30 <% 



c 

 _o 

 Y> 



u 



/o 



456 e 9 /O II 12 



FIG. 75. Natrolite (a) ; Apatite. 



N ATROLITE ( Na 2 AUS i 3 O 10 + HjO ) . 

 (Curve a, fig. 75.) 



Reflecting face ground parallel to m. There are maxima at 9.05, 

 9.5, and 10.05 P-> beyond which point the reflecting power remains 

 unusually high to 12/1. 



APATITE (Ca 5 F(PO 4 )s). 

 (Curve b, fig. 75.) 



The reflecting power gradually decreases to 7.5 /*, beyond which point 

 there are maxima at 9.12 and 9.65 /*. 



GLASS. 

 (Curves a, b, c, fig. 76, and curve a, fig. 78.) 



Glass is of such a variable composition that if the various metallic 

 oxides other than of silicon had an effect upon the reflection bands one 

 would expect to observe it. For example, crown glass 0381 contains 

 68.7SiO 2 +i3.3PbO-f i57Na 2 O+2ZnO, while a flint silicate 857 con- 

 tains 2i.9SiO,+78PbO, and a lead glass contains 4.62PbO+8K 2 O 

 +45Si0 2 . 



The following samples show that the variation in the silicate content 

 of the glass has little effect upon the maxima, except that of intensity. 



The curves show a slight curvature at 8.6 to 8.8 /*, a sharp maximum 



