CLA SSIFICA TION OF IGNEO US ROCKS 67 5 



Furthermore 



Fe O 



CaO d + CaO a 



must be satisfied by transferring Fe 3 3 from Fe 3 3 (hematite), 

 or from FeO.Fe 3 3 (magnetite). 



The liberated FeO with (Mg.Fe)O from hypersthene or 

 olivine must be transferred to satisfy the ratio 



(Mg,Fe)0 



CaO d + CaO a 



D 



Si0 2 must be adjusted in the manner already indicated for 

 the case of pyroxene. 



&) The calculation of the more alkalic amphiboles which 

 occur in rocks rich in soda and iron and comparatively poor in 

 lime and magnesia is to be made in the following manner : 



Sufficient acmite molecules are transferred to satisfy the 

 ratio 



Fe 2° 3 _ D 



CaO d ± CaO a 



Equal Na 3 from acmite plus sufficient Na 3 from soda 

 feldspars is transferred to satisfy the ratio 



Na 2 



CaO d ± CaO a 



D 



Al 3 O s equal to Na 3 transferred from soda-feldspars is 

 liberated and enough of it is transferred to amphibole to satisfy 

 the ratio 



A1 2 3 



CaO d ± CaO a 



If all the liberated A1 3 3 is not required to satisfy the last 

 named ratio, CaO must be withdrawn from diopside to form 

 additional anorthite, and the sign of CaO an is minus. 



If more Al 3 O s than that liberated from soda feldspars is 

 needed to satisfy the ratio in question additional Al 3 O s with 

 CaO is transferred from anorthite, and the sign of CaO in the 

 expression is plus. 



