THE ROSIWAL METHOD FOR MINERALS 



217 



ings obtained for the different sections are possibly due to differences 

 in the sections themselves, the grain of the rock being coarse enough 

 to show slight variations. The last column shows the average of 

 the sixteen determinations, and not the average of the averages. 



TABLE III 



i(s) 



Hd) 



m (2) 



IV (3) 



V(i) 



VI (2) 



Cross, Iddings, 

 Pirrson, and 

 Washington 



Average 



Quartz. . . . 

 Orthoclase . 

 Plagioclase. 



Biotite 



Hornblende 

 Augite. . . . 

 Magnetite . 

 Apatite. . . . 

 Titanite. . . 



Pyrite 



Zircon 



17.64 

 29. II 

 32.01 

 10.47 



7-47 

 2. 76 



•58 



.09 



07 



04 



21.6 



25-8 



35-6 



9.2 



5-6 



99.99 



99-9 



99.96 



99-94 



99.9 



100.13 



99.98 



99.81 



99-9 



For the separation of the constituents by mechanical means, 

 several methods were employed. The magnetite was first removed 

 by means of an electromagnet.^ By repeating the process the 

 material removed was practically pure. The biotite was next 

 separated by Rosenbusch's^ method of shaking the rock powder 

 from an inclined sheet of semi-glazed paper. A remarkably clean 

 separation resulted as shown by microscopic examination, only a few 

 flat hornblende flakes being included as impurities. The remaining 

 material was now placed in a Brogger-Harada^ tube with about a 

 half-pint of Sonstadt's (potassium-mercuric-iodide) solution, and 

 enough water was added to bring down the hornblende and augite. 

 For the purpose of these experiments it was not necessary to sepa- 

 rate these two minerals, so it was not attempted. With these 

 minerals the zircon, apatite, and titanite came down. Thus 

 far the separation was easy; the difference in color between 

 the heavy minerals and those remaining clearly showed when 



' The instrument is illustrated and the method described in Johannsen's Manual 

 of Petrc graphic Methods, 1918, Fig. 725, and p. 540. 



^ Ibid., p. 5S7- ^ Ibid., p. 551. 



