INFRA-RED TRANSMISSION SPECTRA. 



HYDROTALCITE (Mg 3 Al(OH) 6 +3H 2 O). 



(From Vernon, New York. Lamellar; massive; subtranslucent ; = 0.04 mm. 



Fig. 14.) 



The hydroxide group (OH), to be noticed later on, confuses matters 

 at 3 fji. The other water bands at 1.5, 2, and 4.75 /u. are visible in spite 

 of the great opacity, which becomes complete at 6 p.. 



a 



FIG. 15. Varicite (a) ; Wavellite (b and c). 



VARICITE (A1PO+2H S O). 



(Massive; blue color; subtranslucent in thin section of 0.03 mm. From Lewiston, 



Utah. Fig. 15.) 



In this mineral the water bands at 1.5, 2, and 4.75 ju, are almost obliter- 

 ated. Those at 3 and 6 p are shifted and are no doubt composites. 

 From this and other minerals studied, having the PO 4 group, there is no 

 marked evidence of an absorption band belonging to this group. 



WAVELLITE (AlOH),(POO.+5HaO. 



(Crystallized in rays of needles; section ground parallel to rays; subtranslucent. 



From Arkansas. Fig. 15.) 



The lack of homogeneity of the crystals renders this mineral very 

 opaque. The water bands at 1.5 and 2 /* are visible, in spite of the 

 complete opacity at 3 /u.. This great opacity appears to be a characteris- 

 tic of the phosphates, as has already been observed in the borates. 



