  At high temperature and pressure, solid diffusion and chemical reactions
between rock minerals lead to phase transformations. Chemical transport during
uphill diffusion causes phase separation, that is, spinodal decomposition.
Thus, to describe the coarsening kinetics of the exsolution microstructure, we
derive a thermodynamically consistent continuum theory for the multicomponent
Cahn--Hilliard equations while accounting for multiple chemical reactions and
neglecting deformations. Our approach considers multiple balances of
microforces augmented by multiple constituent content balance equations within
an extended Larch\'e--Cahn framework. As for the Larch\'e--Cahn framework, we
incorporate into the theory the Larch\'e--Cahn derivatives with respect to the
phase fields and their gradients. We also explain the implications of the
resulting constrained gradients of the phase fields in the form of the gradient
energy coefficients. Moreover, we derive a configurational balance that
includes all the associated configurational fields in agreement with the
Larch\'e--Cahn framework. We study phase separation in a three-component system
whose microstructural evolution depends upon the reaction-diffusion
interactions and to analyze the underlying configurational fields. This
simulation portrays the interleaving between the reaction and diffusion
processes and how the configurational tractions drive the motion of interfaces.
