THE MINERALOGRAPHY OF THE FELDSPARS 221 
the method explained in the Appendix, the crystals will be found 
to have a composition of R through S toward A, as the tempera- 
ture falls from T to T,. The composition of the liquid on the other 
‘ 
we — - b- - ee 
| 
1 
L 
‘ 
\ 
' 
e 
iy 
‘ 
' 
t 
\ 
iy 
t 
t 
H 
Fic. 4.—Thermo-equilibrium diagram of the potash-soda series, based upon a weight percentage 
(after Warren). 
hand is indicated by the line NOE. Let us examine the crystal— 
a solid solution, which is of variable composition provided there 
is no readjustment taking place between the crystal phases and 
