366 THE VEKMILION IR0N-J5EARING DISTRICT. 



granite are quartz, feldspar (both ortlioclase and plagioclase), augite, liom- 



blende, inica, spliene, apatite, magnetite, and hematite. The phenocrysts are 



of plagioclase. Most of the minerals have their normal characters and will 



not be described. The feldspar and augite are somewhat exceptional, and 



have been described in detail by Mr. Grant,* from whose description the 



following details concerning these are taken. 



Grant's study of the feldspar shows that the plagioclase has a specific 



gravity ranging from 2.58 to 2.62 and the chemical composition shown 



below.** 



Analysis of feldspar of Oaxiaquahic granite. 



Per cent. 



SiOj 67.99 



AlA 19.27 



FeA 82 



CaO 75 



MgO 02 



KjO 3.05 



NsLjO 6.23 



HjO 90 



Total 99.03 



From this he concludes that the feldspar is an anorthoclase composed 

 of orthoclase, albite, and anorthosite molecules in the following propor- 

 tions: Org, Abi4, Aui. 



The augite varies from a colorless one to a variety having a bottle- 

 green color. The colorless kind is not uncommonly intergrown with the 

 green variety. Sometimes this is in zonal intergrowth. The individuals 

 possess a very good crystallographic development. The specific gravity of 

 the augite as a whole is somewhat higher than 3. An analysis of the 

 augite given by Grant is here quoted: 



Analysis of migite of Oaeaqudbic granite. 



Per cent. 



SiOj 53.19 



AlA - 2.38 



FeA 9-25 



FeO 5.15 



CaO o 17.81 



MgO 9.43 



KjO 38 



Na,0 2.63 



H^O 01 



Total 100.23 



«Geol. and Nat. Hist. Survey of Minnesota, Twenty-first Ann. Eep't., 1892, pp. 47-48. i'lbid., p. 44. 



