62 



GEORGE I. FIN LAY 



In accordance with its formula K20.Al20j.6Si02, in the propor- 

 tions 1 : 1 :6, for orthoclase, K^O, 53, takes 53 Al^Oj and six times as 

 much SiOj. In the same way albite, NaaO.Al^ 03.68102, in the 

 proportions 1:1:6, with Na^O, 60, takes 60 molecular-proportion 

 units of AI2O3 and 6X60 of SiO^. Anorthite, CaO.Al203.2Si02, 

 in the proportions 1:1:2, is made with 20 CaO, 20 Al^Oj, and 40 

 SiOj. Of AI2O3, 3 molecular-proportion units are left for corundum. 

 Of SiOg, 557 molecular-proportion units are left to form quartz. 

 The percentage weights for the calculated minerals have been obtained 

 from the second set of tables, pages 247-59, by looking up for ortho- 

 clase (or), the amount of K^O, 53; for albite (ab), the amount of 



ANALYSIS A 



ToscANOSE (Aplite). Professional Paper 14, p. 172, No. 122 



Dargo, Victoria, Australia 



NaaO, 60; for anorthite (an), the amount of CaO, 20; for corundum 

 (C), the amount of AI2O3, 3. To get quartz we multiply the amount 

 of SiOj left over for it (557), by 60, the molecular weight of quartz. 

 With abundant silica then and with AI2O3 greater than KjO-f 

 NagO-f-CaO we make orthoclase, albite, anorthite, corundum with 

 extra AI2O3, and quartz with extra Si02. 



The sum of the percentage figures of the analysis, H2O being 

 1. 01, is 101.12. The sum of the calculated minerals in the norm 

 with H2O added in is 101.21, and for every calculated analysis these 

 two should correspond as closely as i per cent, or 2 per cent. The 

 correspondence cannot be numerically absolute, but it gives us a 

 valuable check on the correctness of the calculation. 



