WATER OF CRYSTALLIZATION. 25 



SCOLECITE (CaAl 2 Si s O, +3H 2 O). 



(Monoclinic section split parallel to m; perfectly transparent; t = 0.565 mm. 



Curve b, fig. 8.) 



This mineral differs from the preceding in being a lime zeolite, and 

 in having one more molecule of water. Its greater homogeneity makes 

 it more transparent in the region of the short wave-lengths. It has the 

 general outline and the absorption bands of the water curve up to 5 /*, 

 where it is completely opaque. The 3 /* band is evidently complex. 

 Prof. S. L. Penfield kindly presented this specimen. 



80 %r 



23456 



FIG. 9. Analcite (a); Colemanite. 



ANALCITE (Na 2 Al 2 Si4O 

 (Cut perpendicular to optic axis; subtransparent ; f = o.ii mm. Fig. 9.) 



This specimen, made by Steeg & Reuter, was small and broken in 

 shipping, so that by placing two pieces end to end the spectrometer 

 slit was not quite covered. Nevertheless it shows a transparency farther 

 into the infra-red than is usual. As a whole, however, it is very opaque 

 (curve a, fig. 9), and the water bands at 1.5, 2, and 4.7 p. are quite 

 obliterated. There seem to be no other than water bands. 



COLEMANITE (Ca 2 B 8 On+5H 2 O). 

 (Cut parallel to b; transparent; / = 0.268 mm. Curve b, fig. 9.) 



This mineral is obtainable in large transparent crystals. Neverthe- 

 less, it is unusually opaque to infra-red radiation, so that very little 



