346 University of California Publications. [Geology 



ANALYSIS OP MINETTE. 



SiO, 



53 



69 



A1A 



25 



86 



Fe.O, 







FeO 



1 



71 



MgO 



1 



91 



CaO 





65 



Na 2 





89 



K 2 



8 



11 



BaO 





37 



P 2 5 





25 



Fe 





88 



S 



1 



01 



co 2 





11 



H 2 



3 



66 



F 





07 





99 



17 



From this analysis the following percentage of minerals in 

 the rock has been calculated as probably representing its com- 

 position although the estimate is not altogether satisfactory: 



Orthoclase 



31 





Albite 



7 





Anorthite 



1 





Biotite 



17 





Muscovite 



8 





Corundum 



4 





Apatite 





2 



Calcite 





2 



Pyrite 



2 





Kaolin 



21 





Free Silica 



8 







99. 



4 



From this it is evident that the rock, although much kaolin- 

 ized, pyritized, silicified, and otherwise altered, is rich in ortho- 

 clase and biotite and corresponds in a general way with what 

 might be expected of a much altered minette. The high content 

 of alumina in the analysis can only be accounted for on the as- 

 sumption that some of that oxide exists in the rock uncombined, 

 thus confirming the microscopic detection of corundum. 



