34 



tabular parallel to the base , the faces of this form are not 

 infrequently somewhat uneven so as to give multiple and indistinct 

 reflections. The prism of the second order, и, occurs only on 

 the protuberant middle part of the larger crystals. On the 

 smaller crystals this form has not been observed. Its faces 

 are always dull. The hexagonal bipyramid is present under 

 the same circumstances as the preceding form. Its faces are 

 likewise dull. 



The rhombohedral forms may be grouped into positive and 

 negative forms as follows. 



Positive Negative 

 i = {пОб} 



t = {2029} и = {2209} 



([ = {lT02} 



r = {2203} 



V = {ЗОЗ4) у = {Ш\} 



p == {loTij 



z = {4043} 



a = {3032} ß = {3302} 



r = {3301} 



To the positive forms t, v and a correspond, as will be 

 observed, respectively the negative forms u, у and ß. The nega- 

 tive forms i, g', r and у have no corresponding positive , and 

 the positive forms p and z no corresponding negative forms. 



Common to the South American parisite and the Green- 

 land mineral are only the forms c, ш, r, p and s. Conse- 

 quently the other forms observed by me would be new for 

 parisite. Most of the other forms occurring on the parisite 

 of Muso are hexagonal bipyramids (of the second order). Such 

 forms are also present on the Narsarsuk mineral, though it 

 was not, from reasons stated above, possible to determine 

 them. It is, therefore, probable that several more forms are 

 common to the minerals from the two localities. 



As G. Nordenskiöld has shown, twin formation is verv 



