THE MINERALOGRAPHY OF THE FELDSPARS 287 
amount of the crystals of pure N and of the small crystals 
which constitute the eutectic mixture, and “sliding” back up the 
lines until A is reached. 
Y 
eS ES SS ES SS ee ee 
N 10 20 3040 50 60 70 80 90 N 
M90 80 70 60 SO 40 30 20 10 Mm 
PERCENTAGE COMPOSITION 
uJ 
ie 
=) 
FE 
< 
x 
Wl 
Oo. 
= 
uJ 
E 
Fic. 17.—Thermo-equilibrium diagram of a eutectiferous system 
