94 ALBERT JOHANNSEN 



Example 2. — A syenite having 



Percentage quarfeloids to mantes 79, therefore Class 2. 

 Ab s An 3 =Ab6 2 . s An 37 . s , therefore Order 2. 



Quartz less than 5 per cent, therefore between Families 11 

 and 15. 



;=—=—, therefore Family 12. The rock number is 



CaM 18 23 



2212; that is, Class 2, Order 2, Family 12. The values 76, 22.8, and 

 1 . 2 are used in the graphical location of the rock. 



Example 3. — A nephelite-syenite with 



Kf 21. s = 39.0 



., A (Naf 31.0I ,, 



Ab 92 An 8 ^ , ° } =61.0 



Caf 2.5 



Total feldspar 55.0 100. o 



Neph 27.5 



Sodal 8.5 



Total f eldspathoids 36.0 



Total quarfeloids 91 .0 



Aeg.-aug 5.0 



Biot 2.5 



Acces 1 . s 



Total mantes 9.0 



Quarfeloid ratio 91. Class 2. 



Ab 92 An 8 Order 2. 



36 39. 5 



Foids to feldspars = — = . Between Families 21 and 2Z. 



* 55 60.5 



