WATER OF CONSTITUTION. 



47 



do not give coincident results, but there being no bands near those of 

 water, it did not seem worth while to make further inquiry. 



CHLORITOID (H 2 (MgFe)Al 2 SiO 7 ). 



(Variety, masonite; cleavage piece parallel to c; transmits blue-green; t = o.2$- 



Curve b, fig. 33.) 



This mineral is very opaque to infra-red radiation. There are sev- 

 eral small absorption bands, viz, at 2.3, 2.6, 3.3, 5, 6, and 6.3 /*, as in the 

 preceding. The point of interest is the absence of bands at 1.5 and 3 /*. 



/ 234-567 6JU 



FIG. 33. Pectolite(a); Chloritoid 



CUNOCHLORE (HsMgsAlaSiaOis) J PfiNINlTS (HsMgFe) 6 Al 2 Si 8 Oi). 



(Clinochlore: t = o.o8. Peninite: curve b, t = o mm. Fig. 34.) 



These two minerals belong to the chlorite group, which is related to 

 the micas, to be noticed presently. These minerals contain about 12 

 per cent of water, which is given off at a high temperature. Their 

 transmission curves are unusually similar to those of the micas. There 

 are absorption bands at 2.9, 5.9, 6.3, 7.1, and 7.8^. The frequently 

 recurring bands at 2.9 and 5.9 p, with the metallic reflection band at 8.5 

 and 9.02 fi, remind one of harmonic series. 



It may be that these bands belong to a slowly conveying spectral 

 series, if not a harmonic series, for the first band oscillates between the 

 values 2.8 and 2.95 /*, while the next band shifts from 5.6 to 5.9 /A, as 

 will be noticed in the micas. 



As already mentioned, the constitution of many minerals is still doubt- 

 ful. Clinochlore is one of these. From investigations made by Clarke 

 and Schneider, it was inferred that the hydroxyl groups MgOH and 



