96 



The fundamental prism, on the contrary, is of rare occurrence and 

 always subordinate. All the faces are very brilliant, but seldom 

 perfectly even. The base is, as it were, broken into several 

 fields which are not quite in the same plane. The pyramidal 

 faces are generally striated longitudinally and, therefore, seldom 

 give simple reflections. 



Below are given the measurements obtained on some small 

 crystals that gave tolerably simple and sharp reflections. 



1012) : (0( 



)0l) = 37° 52' 

 37° 33' 

 38° 9' 

 37° 45' 

 37° 40' 

 37° 32' 

 37° 40' 



(lOlO) ; 



: (OOOl) = 



- 57° 26' 

 56° 45' 

 57° 8' 

 57° 2' 

 56° 51' 

 56° 51' 

 56° 26' 



Mean = 37° 45' Mean = 56° 26' 



According to the axial ratio calculated for the Norwegian 

 catapleiite 



a:c= 1:1 ,3629, 



the calculated angular values become respectively 38° 12' and 

 57° 34'. There is here a real difference, as all the values found 

 by me are loAver than those calculated from the above-mentioned 

 axial ratio. 



However, these crystals seem to be only apparently hexa- 

 gonal. The middle edge, Avhich should be the combination-edge 

 between (lOll) and (lOlT), proves to be, on most of the 

 crystals, a twinning-line between two halves with the base as 

 composition-face. That the middle edge is in reality a twinning- 

 line, is shown by the fact that the tAvo halves do not quite 

 cover each other, one of them reaching a little beyond 

 the other at the edge. Narrow strips of the basal planes 

 turned inwards are thus alternately visible round the crystal. 



