  Several emergent phenomena and phases in solids arise from configurations of
the electronic Berry phase in momentum space that are similar to gauge field
configurations in real space such as magnetic monopoles. We show that the
momentum-space analogue of the "axion electrodynamics" term
$\mathbf{E}\cdot\mathbf{B}$ plays a fundamental role in a unified theory of
Berry-phase contributions to optical gyrotropy in time-reversal invariant
materials and the chiral magnetic effect. The Berry-phase mechanism predicts
that the rotatory power along the optic axes of a crystal must sum to zero, a
constraint beyond that stipulated by point group symmetry, but observed to high
accuracy in classic experimental observations on $\alpha$-quartz. Furthermore,
the Berry mechanism provides a microscopic basis for the surface conductance at
the interface between gyrotropic and nongyrotropic media.
