114 







Molecular ratios 





SiO, 



58,68 



0,9780 





16 



Al, 0, 

 Fe,0, 



10,24 



4,02 



0,2008 ] 

 0,0510 J 



^ 0,2510 



4 



MnO 



0,31 



0,0020 • 







Li,0 

 K,0 



8,24 

 11,05 



0,2747 

 0,1175 



0,4202 



7 



Na,0 



1,61 



0,0260 . 







F 



8,16 



0,4294 





7 





102,31 









3,44 









98,87 



This gives for the mineral the following empirical formula: 



(Al, Fe), [Li,, К,, Na,), F, Si,, О,,. 



This analytical result agrees fairly well with that obtained 

 by Lorenzen for polyUthionite. The only important difference 

 is that in the mineral from Narsarsuk sodium is almost entirely 

 replaced by potassium. This is the more remarkable as in 

 the Narsarsuk minerals in general sodium is decidedly the 

 predominating alkali metal. The composition of polyUthionite 

 differs from that of common zinnwaldite by a higher percentage 

 of alkalies, especially of lithia, owing to which the percentage 

 of silicic acid is also larger. 



It has not been fully ascertained that zinnwaldite occurs 

 elsewhere on Narsarsuk than at the locality No. 2. The mineral 

 is found there implanted on feldspar as well as on elpidile. 

 Occasionally the zinnwaldite tables are in part imbedded in the 

 feldspar crystals. This does not, however, prove that the 

 whole of the feldspar is later than the zinnwaldite or formed 

 simultaneously with it. The fact is that at a comparatively late 

 period of formation, when the zinnwaldite, which no doubt is 

 of secondary origin, had already crystallized out, feldspar 



