1 55 



The mineral occurs only as crystals; on account of its 

 eminent cleavage, however, the crystals are highly subject to 

 being broken or split. One, therefore, seldom meets with whole 

 crystals, but mostly only fragments. These fragments, however, 

 present, on the whole, the same forms as the unbroken crystals 

 and are bounded by the same faces. 



The crystals belong to the tetragonal system and, probably, 

 to the bipyramidal class of this system. From the angle 



(111) : (110) = 53° 29' 



is calculated the axial ratio 



a:c= I : 0,52352. 



The crystals are bounded by the following forms: 



c = {00l}, a = {lOO}, m = {llO}, w = {2lO}, ^9 = {ill}. 



The base is generally the predominant form. Therefore the 

 crystals are almost always tabular parallel to this form. Only 

 on very small crystals do the prismatic faces sometimes attain 

 the same size as the basal faces. The crystals are then of a 

 cubic form ; occasionally they may even be of short prismatic 

 habit parallel to the с -axis. Among the faces in the vertical 

 zone the prism of the flrst order ш is in the majority of cases 

 the predominant form. The prism of the second order a then 

 appears as a truncation of the vertical edges. The tetragonal 

 prism of the third order n is rather rare , it is always repre- 

 sented by narrow planes, sometimes it occurs only as a stria- 

 tion in combination with the other vertical faces (Fig. 5, Plate 

 VllI). This tetragonal prism has never been observed repre- 

 sented by the full number of faces, but always, even when 

 several of its faces occur on the same crystal , only on one 



Gieenlanders who accompanied me during my excursion in 1897, the 

 only pronunciation that I ever heard. This is also the reason why the 

 form Narsasuk is used in the account of my journey in this Journal, 

 Vol. 14 p. 251. 



