62 



Type I. (Needle-shaped crystals). 



By far the greatest number of the epididymite crystals 

 occurring on INarsarsuk have an elongated, needle-like shape. 

 They are generally small, seldom attaining more than half a 

 cm. in length and 1™™ or two in thickness. The faces in the 

 zone of the longitudinal axis are in general strongly striated; 

 owing to this the more subordinate among them are sometimes 

 difficult to determine. The faces that bound the crystals at 

 the ends , on the other hand , are in most cases very well 

 developed. 



All forms previously observed by me on epididymite from 

 Narsarsuk were found on crystals belonging to Type I. The 

 position originally given to the crystals was such that their 

 longitudinal direction coincided with the crystallographical b- 

 axis, the most distin'ct cleavage of the mineral with the third 

 pinacoid (OOl), and the somewhat less distinct cleavage with 

 the first pinacoid {lOO}. With this position the axial ratios 

 calculated from the angles 



(310): (100) == 30° 4' and (201): (001) = 46° 53' 

 are as follows : 



a:b:c == 1,7367 : 1 : 0,9274. 

 The axial ratios estabhshed for the monoclinic eudidymite, 

 which is identical in chemical composition with epididymite, 

 are the following: 



a:b:c = 1,71069 : 1 : 1,1070; ß == 93° 45 V2'. 

 Now, a somewhat greater agreement between the axial 

 ratios of the two minerals is obtained by interchanging the 

 a- and ô-axes of epididymite i. e. revolving the crystals 90° 

 about the c-axis and makiug the dome {201) = (ОИ) and the 

 prism {310) = {110}. The axial ratios thus obtained for 

 epididymite are 



a:b:c == 1,7274 : 1 : 1,0680. 



