WATER OP CRYSTALLIZATION. 3! 



VIVIANITE (Fes(PO4)2+8H 2 O). 



(Monoclinic; section ground parallel to b; bluish color; translucent; t = 0.11 and 



0.25 mm. Fig. 16.) 



This section is practically opaque beyond 3 /*. The water bands at 

 1.5 and 2 p. are visible, although slightly shifted, which is due to general 

 transparency of the mineral. This is well illustrated in curve c, which 

 is curve b magnified 5 times. I am indebted to the late Prof. S. L. 

 Penfield for this mineral. 



FIG. 16. Vivianite. 



MEU.ITE (Al 2 COi2+i8H 2 O). (Fig. 17.) 



This mineral occurs as waxy crystals of variable transparency in 

 European coal measures. It was selected on account of its carbon, and 

 also because of the large number of molecules of water, which is 

 expelled at a low temperature. 



In fig. 17, curve a, is given the transmission curve of a mineral from 

 Steeg and Reuter, purporting to be mellite or "honeystone," / = 0.125 

 mm. It was the most flagrant exception to the rule that minerals having 

 water of crystallization are very opaque and have absorption bands in 



