or Lazulite of North Carolina. 

 the others. Fig. 1 represents this distorted 



83 



Fig. 1. 



aspect ; fig. 2 the same form (or combination, if 

 monoclinic) in symmetrical proportions. These 

 symmetrical crystals are of smaller size and less 

 numerous than the distorted forms. 



Although the edges of these crystals are sharply 

 defined, the planes are unfortunately without 

 lustre. The most careful measurements of five 

 crystals, by means of a fixed or Adelmann's go- 

 niometer, gave me the same angles for both the 

 upper and lower faces. The difference found by 

 Priifer is too slight, however, to be satisfactorily 

 detected by any kind of application goniometer. 

 I attached, therefore, thin films of mica as care- 

 fully as possible to the planes of one of the cry- 

 stals, and measured the angles by reflected light 

 with a Wollaston goniometer of the best construc- 

 tion. The following Table (sustaining the apparently trimetric 

 character of these crystals) shows the measurements thus ob- 

 tained : — 



Upper planes over Lower planes over 

 front edge. front edge. 



1st measurement . 



2nd 



3rd 



. . 100 4 

 . . 99 99 

 . . 99 99 



100 



99 99 



100 2 





Upper planes over 

 side edge. 



Lower planes over 

 side edge. 



1st measurement . 



2nd 



3rd 



. . 97 27 

 . . 97 30 

 . . 97 26 



97° 28 

 97 26 

 97 27 



Front planes over Back planes over 

 middle edge. middle edge. 



1st measurement 134 10 

 2nd „ 134 10 



3rd „ 134 8 



134 



ij Whether monoclinic or tri- 

 metric, these measurements 

 134 12 should of course correspond. 



1 Q A 1 A T ' le two sets Tiere ta ^ en : now " 

 loi 1U ever, for greater satisfaction . 



Adelmann's goniometer gave me 100° — 100° 30' over a front 

 edge, 97°— 97° 30' over a side edge, and 134°— 134° 30' over a 

 middle edge. If we look upon the mineral as trimetric, and 

 adopt the angle of 100° as the mean inclination over a front 

 edge, with 91° 30' for the value of the prism-angle (according 



to general adoption), the following an; 

 obtained by calculation : — 



G2 



'•les and axial relations are 



