CLASSIFICATION OF IGNEOUS ROCKS 



679 



were separated has been analyzed, and this analysis forms the 

 basis for the calculation of the standard mineral composition. 

 It is from Walkerville Station, near Butte, Mont. The thin 

 section measured is from a specimen of very fresh rock taken 

 near the surface twenty feet from the outcrop of the Parrot vein 

 at Butte. 



TABLE VII. 



Si0 2 ... 

 AU0 3 . 

 Fe 2 3 . 

 FeO . . . 

 MgO... 

 CaO. .. 

 Na 2 0.. 

 K 2 0... 

 H 2 0+. 

 H 2 0-. 

 TiO g ... 



p 2 o 5 .. 



MnO... 

 SrO.... 

 BaO . . . 

 Li 2 0... 

 S0 3 . . . 

 CI 



63.88 



15.84 



2. 11 



2.59 



2.13 



3-97 

 2.81 



4-23 

 .66 

 .22 



•65 

 .21 

 .07 

 .02 

 .09 

 tr 



•34 

 tr 



99.82 



Mol. 



I.065 



•155 

 .013 

 .036 



•053 

 .071 



•045 

 .045 



.008 



.OOT 

 .001 

 .000 

 .000 



.004 



Pyr. 



Urn. 



Ap. 



Mag. 



Orth. 



270 



45 



45 



Alb. 



270 



45 



45 



An. 



130 

 65 



65 



Diop, 



Hyp. 



64 



Qu'tz. 



323 



a) The calculatioji of 'the standard mitierals, or norm, is expressed 

 in Table VII. MnO is combined with FeO making 0.037 

 molecules. S0 3 is allotted to FeO to form FeS 3 becauseof the 

 pyrite known to be present in the rock, Ti0 2 to ilmenite, P 2 O g to 

 apatite, Fe 2 3 to magnetite, K 2 to orthoclase, Na 2 to albite, 

 the remaining A1 2 3 (0.065 mol.) to anorthite, the remaining 



