78 



Type I. 



The arfvedsonite crystals belonging here are generally only 

 jmm Qj. ^^Yo in length and less than 1°"^ in thickness. However, 

 individuals of 1^="" in length and thickness h^ve been observed. 

 In habit they are generally short prismatic and often deve- 

 loped on all sides. In general the small crystals are fairly 

 well developed and their faces very brilliant, so that it has 

 been possible to make fairly accurate measurements. A result 

 of these measurements is, that the axial ratios established by 

 Brögger for the Norwegian arfvedsonite, which differ not a 

 little from the axial ratios established for common amphibole, 

 must be accurate enough and apphcable also to the arfvedsonite 

 from Narsarsuk. The arfvedsonite crystals from Kangerdluarsuk 

 are in general measurable only by the contact-goniometer ; 

 therefore the axial ratios proposed for them by Lorenzen^) 

 have no claim to particular accuracy. The axial ratios calculated 

 by Brögger are as follows 



a -Л: с = 0,54957 : 1 : 0,29751. 

 ß = 75° 441/2'. 



The forms observed on the arfvedsonite from Narsarsuk 

 are the following. 



a = {100}, & = {010}, f? = {00l}, m =={110}, e={l30}, 

 ^={021} and /•= {Ги}. 



This combination, with the exception of a, is represented 

 by Fig. 9, Plate IV. 



As already mentioned, the crystals generally are short 

 prismatic parallel to the vertical axis. The fundamental prism 

 m and the second pinacoid b generally are equally developed, 

 so that the crystals have an almost regular hexagonal contour. 

 Sometimes, however, they are flattened and somewhat tabular 

 parallel to the second pinacoid. The faces belonging to the 

 first pinacoid a and the prism of the third order e are rarely 



^) This Journal, Vol. 2, pag. 48. 



