Vol. 4] Lawson. — The Robinson Mining District. 



307 



ANALYSIS OF MONZONITE. 





Weary Flat, 



Hodritsch, 





Nevada. 



Hungary. 



Si0 2 



61. 



69 



61.73 



AL0 3 



17. 



26 



17.45 



FeA 



3 



.53 



5.94 



FeO 



1. 



91 





MnO 





09 





MgO 



1. 



45 



2.29 



CaO 



5. 



49 



4.52 



Na 2 



3. 



,05 



3.12 



K 2 



3 



.88 



3.88 



BaO 





10 





P 2 5 





.34 





CI 





03 





H 2 (ig) 





,73 



1.16 





99 



.55 



100.09 



The mmeralogical composition of the rock as inferred from 

 the analysis may be expressed approximately as follows : 





Per cent. 



Orthoclase 



23.00 



Albite 



26.00 



Anortkite 



22.00 



Hornblende 



15.00 



Quartz 



13.00 



Apatite 



.65 





99.65 



It would appear from this that a very large proportion, if 

 not all, of the orthoclase is present in the form of the large 

 phenocrysts, the matrix of the rock in which these are imbedded 

 having the character, when considered by itself, of a quartz 

 diorite which consolidated at the eutectie point of the cooling 

 magma. The amount of quartz revealed by the analysis is some- 

 what higher than was inferred from the microscopic study of the 

 rock. The presence of small quantities of manganese and ba- 

 rium is noteworthy. In spite of the fact that copper ores occur 

 at the contact of this monzonite with the encasing formations, 

 neither the results of the analysis nor the fresh condition of the 

 rock lend support to the idea that such copper was derived from 

 the monzonite. The absence of sulphides is a noteworthy feature 

 of the rock, and is a point of striking contrast with other igneous 



