Consider four minerals P, Q, R and S in a three component chemical system (A-B-C) as shown in the figure. For a crossing tie-line relationship, the variance (degrees of freedom) of the equilibrium mineral assemblage at X is R S c B
Four minerals are stable at X, so number of phases (P) = 4
Components (C) = 3
using Gibb's phase rule,
C+2=P+F
F = C+2-P = 3+2-4 = 5-4 = 1
so degrees of freedom is 1.
For cros...