Fairbanks.] Geology of Point Sal. 33 



Minerals. 



Proportion. 



Specific gr. 



Estimate used 



Product 





43-3 



2.50-2.67 



2-57 



1. 11 



Augite 



3 2 -3 



3-338 



3-33 



1.07 



Analcite 



20.O 



2.261 



2.24 



•43 





4.0 



5.0 a 



5 



.20 





O.4 



3.20 a 



3.20 



.or 





IOO 



a Assumed. 





2.82 









2.782 



The following table gives the composition of the rock as com- 

 puted chiefly from the analyses. In place of the analysis of the 

 feldspar, one slightly more acid is taken, corresponding to Ab, An t 

 plus water. The results agree fairly well with the determined com- 

 position of the rock as a whole. It is clear that in one where so 

 much alteration has taken place, it is impossible to harmonize 

 the proportions of all the constituents. 





Feldspar. 



Augite. 



Analcite. 



Magnetite. 



Apatite. 



Computed 

 Composition. 



Rock 

 Analysis. 



Si0 2 



23.18 



15-14 



10.88 







49.20 



49- 6 1 



Al,O s 



I2.02 



3-i6 



4.61 







19.79 



19 18 



FeO 





i-53 





3-3i 





4.84 



5.01 



Fe 4 O s 





•30 





1.69 





I.99 



2. 12 



CaO 



4.21 



6.91 



■05 





•23 



II.40 



10.05 



MgO 





4.48 









4.48 



4-94 



Na 2 



2-45 



•39 



2.68 







5-52 



5.62 



K 2 



■19 





•05 







•23 



1.04 



p 2 o 5 











■27 



•27 



.27 



Ig- 



1-25 



-39 



i-73 







3-37 



3-55 



Total 



43-30 



32.30 



20.00 



5.00 



.40 



101 .09 



101.39 



Petrographic Relations. — The main object of the detailed chemi- 

 cal study was to gain some help in reaching a correct view of the 

 original composition of the rock. In the case of the teschenites of 

 Europe, it is believed by many that the analcite has been formed 

 wholly at the expense of the feldspar, and that there is no evidence 

 of its having replaced a soda rich mineral such as nepheline- 

 Although Rosenbusch, Teall and others have held the view of the 

 original presence of nepheline, the general tendency has been to 

 narrow the group, and of many to consider all teschenites as only 

 varieties of diabase. The question has to be decided, of course, on 

 the presence or absence of nepheline, and upon the meaning of the 



