294 



Lindgren and Melville — Sodalite- Syenite 



is especially abundant and give a rather exaggerated idea 

 of the quantity of this mineral. 



Besides the already mentioned occurrence of analcite in the 

 feldspar it also fills interstices between the feldspar and soda 

 lite grains in the manner shown in the figures. It is very 

 clear and free from inclusions ; a peculiarity of it is that con- 

 trary to the data usually given its refraction appears stronger 

 than that of the feldspar and sodalite. It always shows a faint 

 double refraction in dark gray and bluish colors and each grain 

 usually divides into several sectors with different optical orien- 

 tation. The form of the larger grains is triangular or poly- 

 gonal, being molded by the crystallographic faces of the feld- 

 spar and sodalite as shown in the figure. The interpretation 

 of this analcite offers some difficulties. It is not derived from 

 the sodalite ; there is no direct proof to show that it has been 

 derived from nepheline ; if it is an altered nepheline, then 

 this mineral must have been formed later than the sodalite. 

 !No nepheline has been found so far, but it is by no means 

 impossible that other parts of the eruptive mass might con- 

 tain this mineral. Another possibility is that the analcite fills 

 miarolitic cavities in the rock ; it cannot then very well have 

 been derived from any other mineral than the feldspar. The 

 specific gravities of the sodalite and analcite were found to 

 lie extremely close together. They both fell between 2 - 27 

 and 2*23. A special and repeated separation was made of this 

 mixture which resulted in the two minerals being obtained in 

 a relatively pure state. The specific gravity of the sodalite 

 ranges from 2-27 to 2*255 while that of analcite extends from 

 2*26 to 2 - 24. The two products were then analyzed : 



H 2 (at IOC 

 H„0 (above 

 SiO 



•°)... 



III 



Sodalite. 



0-45 



3-73 

 41-56 



4-79 

 29-48 



0-49 



0-49 



0-15 

 19-21 



0-91 



IV. Analcite 



100°). 



--- 



(7-07)* 

 49*54 



CI 



Al O 







1-67 



25-07 



FeO 



CaO 



MgO : 



Na 2 







0-40 



0-22 



0-20 



15-32 



K,0 







0-89 











Excess 



101-26 



1-08 



100-00 





*By 



diffe 







100-18 

 rence. 





