THE MINERALOGRAPHY OF THE FELDSPARS 



297 



An attempted recast results in the absurd sum of 109.69 per cent 

 for the total feldspar and a deficiency of 7.49 per cent SiOa and 1.2 1 

 per cent AI2O3, as is shown in Table III : 



TABLE III 



Makinen^ has already questioned the value of this analysis when 

 he says (in translation): "The occurrence of a monoclinic sodium 

 feldspar was recently regarded by Barbier and Prost as proved 

 because they found a so-called monoclinic feldspar from Kragero 

 which contains 1 1.74 per centNazO, 0.78 per cent CaO, and only 1.15 

 per cent K2O. The sum of KzO+NajO+CaO, over against SiOa and 

 AI2O3 is still altogether too low and their analysis is to such a degree 

 defective that they themselves can scarcely regard it as satisfactory." 

 It is of course quite possible that their analysis is indeed defective, 

 but when the possibility is considered of nephelite-carnegieite being 

 present, then the results of recasting are understandable as in Table 

 IV: 



Still there is room for improvement. Can it be that the presence 

 of hex:agonal nephelite in a soda-rich feldspar to the extent of nearly 

 9 per cent renders the whole monoclinic, without the possibility of any 

 dimorphism of NaAlSi^Ps ? Possibly. The writer is unable to offer 

 any suggestion that bears on this question. 



The writer endeavored to secure from Dr. Schaller^ definite 

 information regarding barbierite. Dr. Schaller reported^ that the 



'Eero Makinen, "tjber die Alkalifeldspate," Geol. For en. Forhandl., XXXIX, 

 H. 2 (February, 1917), 122. 



^ Through Mr. English of Ward's Natural Science Establishment. 

 3 August 8, 1918. 



