WATER OF CONSTITUTION. 



MANGANITE, MnO(OH). 

 (Orthorhombic; ground parallel to m; opaque; t = 0.08 mm. Fig. 26.) 



As will be noticed in curve a of fig. 26, manganite has no sharp bands 

 throughout the whole region to 9^. There is a light indication of a 

 band at 3 ^ and another at 6.2 /*. 



23*56789 



FIG. 26. Mauganite (a) ; Gothite (b}\ Bauxite (c). 



10 



GOTHITE, FeO(OH). 

 (Section ground parallel to b; = 0.15 mm. Curve b, fig. 26.) 



The appearance of this mineral is opaque black, metallic luster, and 

 as a whole would not impress one as being quite transparent to 9 /A. 

 It transmits about 20 per cent of the energy throughout this whole 

 region, which is in marked contrast with the almost complete opacity 

 of iron. The 3 ^ band is well marked, while a second one occurs at 9 //.. 

 This specimen was kindly presented by the late Prof. S. L. Penfield. 



30 



C 



IT, 



to 



7 



V 



4-56 

 FIG. 27.- Turquoise (a) ; Lazulite. 



BjU 



BAUXITE (AUO(OH)O. 

 (Chocolate-brown color; / = o.u mm. Curve c, fig. 26.) 



In this mineral the 3 /* band is wide and complex. There are other 

 bands at 4.7, 5.8, and 7/t. 



