THE MINERALOGRAPHY OF THE FELDSPARS 245 
Fic. 10.—The ternary diagram of the potash-soda-lime feldspar, after Vogt. 
The first diagram is the perspective method of representing the solid model. The 
one to the right is the projection of the same to the base. The lower diagram shows 
the change in composition during crystallization. The circles represent the composi- 
tion of the first-formed feldspars, the arrows show the direction of the change in 
composition taken by the subsequent forming minerals, and the arrow heads them- 
selves indicate the composition of the last-formed minerals. 
