28 



INFRA-RED TRANSMISSION SPECTRA. 



was split into two inclined prisms, which, when placed end to end, 

 made a tight joint. The transmission curve, a, shows all the absorption 

 bands of water in their proper intensities. A new band occurs at 2.6 /i 

 which widens the one at 3 /u, but does not displace it. The specimen 

 suddenly becomes opaque at 6 p.. 



GISMONDITE (Hi(Na 2 Ca)Al 2 Si6Oi 8 +4H 2 O). 



(Stalactitic mass; subtranslucent ; f = 0.245 mm. From County Antrim, Ireland. 



Fig. 12.) 



This specimen was not very homogeneous, but, in spite of its great 

 complexity chemically, it is fairly transparent. The only bands present 

 are those due to water at 1.5, 2, 3, and 4.7/4. The band at 3;* is very 

 wide, which suggests the presence of others, perhaps of silicon, at 2.9 /i. 



60% 



Z 3 4 5 6 



FIG. 12. Thomsenolite(a); Gisraondite. 



QLJU 



BLODITE (MgSCXNaSO^HjO). 

 (Cut perpendicular to axis; t = 0.10 mm. Curve a, fig. 13.) 



This mineral shows all the water bands, the one at 2/x being con- 

 spicuous for its sharpness. The band at 4.6 is composite, due to the 

 SO 4 band at 4.55 //,, as will be shown in discussing the sulphates, while 

 the 3 n band is also complex. 



THAUMASITE (CaSiO 3 CaCO 3 CaSO-r-i5H 2 O). 

 (Cut perpendicular to axis; transparent; t = 0.125 mm. Fig. 13.) 

 This mineral is too opaque for heat rays to be considered in demon- 

 strating the presence of water of crystallization. The water bands at 



