THE NORM IN IGNEOUS ROCKS 



89 



Kaliophilite takes only half as much silica to go with a like amount 

 of K2O.AI2O3 as leucite would take, and only a third as much as 

 orthoclase. 



ANALYSIS R 



Venanzose (Euktolite). Professional Paper 14, p. 357, last analysis 



San Venanzo, Umbria, Italy 



It will be noted that the series of analyses from J to R inclusive 

 illustrates a series of alternative methods for dealing with low SiO^. 

 A slight deficit may be adjusted between hypersthene and olivine. 

 By this device we can do away with a silica deficit equal to one-half 

 (MgFe)O. A larger deficit may be provided against by making 

 albite with nephelite after having made orthoclase, under the condi- 

 tions given above. This saving of silica amounts to a little less than 

 four times the Na^O. A still larger deficiency in SiO^ may be 

 provided for by allotting for orthoclase and leucite after making 

 nephelite. Our making nephelite first in this case saves us an 

 amount of SiOa equal to four times the units of NajO, and the sub- 

 sequent distribution saves a little less than two times the amount of 

 K2O. With silica still lower it is necessary after making leucite 

 and nephelite, thus saving two times the units of K^O plus four times 

 the NaaO, to bring in ackermanite, a device which then saves three 

 fourths of a unit of SiOz for every unit of CaO taken from diopside 

 for ackermanite, or one silica on every four converted from wollastonite 



