  We examine the structure of cool magnetic spots in the photospheres of
evolved stars, specifically asymptotic giant branch (AGB) stars and R Coronae
Borealis stars. We find that the photosphere of a cool magnetic spot will be
above the surrounding photosphere of AGB stars, opposite to the situation in
the sun. This results from the behavior of the opacity, which increases with
decreasing temperature, opposite to the behavior of the opacity near the
effective temperature of the sun. We analyze the formation of dust above the
cool magnetic spots, and suggest that the dust formation is facilitated by
strong shocks, driven by stellar pulsations, which run through and around the
spots. The presence of both the magnetic field and cooler temperatures make
dust formation easier as the shock passes above the spot. We review some
observations supporting the proposed mechanism, and suggest further
observations to check the model.
