CLASSIFICATION OF IGNEOUS ROCKS 



5 



The approximate chemical composition of this rock is found 

 by separating each of the minerals observed in the rock into its 

 chemical components. The results are given below : 



TABLE XI. 



■CO. zCu 3FeS 2 4Zr0„ 



The chemical composition of the second rock from Butte in 

 which the minerals were measured is given in the same table, 

 and also the analysis of Butte granite from the Atlantic Mine. 

 The similarity of the results is an indication of the success of the 

 process in this instance. 



With the data here assembled it is possible to classify the 

 rock from near the Parrot vein with almost as much accuracy as 

 though it had been analyzed chemically. In other cases the 

 data may not be so nearly correct, but the error in many cases 

 will be quite within the limits of variation for the division of the 

 classification to which the rock belongs. 



It is evident that there is need for more chemical work 

 upon the component minerals of igneous rocks and the correla- 



