650 CROSS, ID DINGS, PIRSSON, WASHINGTON 



18. To A1 2 3 and K 3 + Na 2 is allotted SiO s to make 

 polysilicate, orthoclase, albite (K, Na) 2 . A1 2 3 .6 Si0 2 . 



a) If there is excess of Si0 2 it is added to the orthosilicate 

 of (Mg, Fe)0 to raise it to the metasilicate (Mg,Fe)0 .Si0 3 . 

 If SiO s is insufficient to convert all the olivine into hypersthene 

 it is distributed according to the following equations : 



x -\- y = molecules of (Mg,Fe)0. 



y 



x A — = available SiO„ . 



2 * 



where x = hypersthene, y = olivine molecules. 



&) Further excess of Si0 3 is to be allotted to TiO s and CaO 

 to form titanite. These constituents remain as perofskite when 

 there is no excess of Si0 2 . 



c) Further excess of Si0 2 is reckoned as quartz. 

 19. If there is insufficient Si0 2 to form polysilicate feldspar 

 out of all the K 2 and Na 2 with Al 2 O s : 



a) To K 2 O.Al 2 O s is allotted tentatively enough Si0 2 to 

 form polysilicate, orthoclase (K 2 . A1 2 3 . 6SiO s ) and the 

 remaining Si0 2 is distributed between albite and nephelite 

 molecules by means of the equations : 



x -\- y — molecules of Na 2 0. 

 6x -f- 2y = available Si0 2 . 



where x = albite, and y = nephelite molecules. 



b) If the available Si0 2 in case 15, a) is insufficient to form 

 nephelite with the Na 3 0, then enough Si0 3 is first allotted to 

 the Na 2 to form nephelite and the remaining Si0 3 is distrib- 

 uted between orthoclase and leucite molecules by means of the 

 equations : 



x -\- y = molecules of K 2 0. 

 6x -\- \y = available Si0 2 . 



where x = orthoclase, and y = leucite molecules. 



20. If there is insufficient Si0 2 to form leucite and nephelite 

 with olivine it is necessary to reduce a sufficient number of 

 molecules to form the subsilicate akermanite, 4Ca0.3Si0 2 . 



a) In case there is no wollastonite this is done after dis- 



