THE MINERALOGRAPHY OF THE FELDSPARS 243 
AB and CD intersect at point P. Through P the line EF is 
drawn parallel to the remaining side, ML. The point P represents 
the composition of this ternary system. By consulting the 
figures at the side of the triangle the method of representation is 
made clear. 
90 _ 80 70 60 50 40 350 O 
ay 
(0 _ 29 30 40 50 60 70 60 90 
Fic. 9.—Ternary diagram, illustrating the method of indicating by a point (P) 
the composition of a specimen consisting of 50 per cent of L, 30 per cent of M, and 20 
per cent of V. ; 
By means of such triangular diagrams we can represent in a 
most direct manner the thermo-equilibrium diagram of a three- 
component system. If we employ a sufficient number of these 
figures we could discuss the complete feldspar system with the aid 
of the phase rule. The following are the ternary systems that 
would be necessary to that end: (1) potash-soda-lime, (2) potash- 
soda-barium, (3) potash-soda-carnegieite, (4) soda-lime-barium, 
