  We investigate the phase behavior and kinetics of a monodisperse mixture of
active (\textit{i.e.}, self-propelled) and passive isometric Brownian particles
through Brownian dynamics simulations and theory. As in a purely active system,
motility of the active component triggers phase separation into a dense and a
dilute phase; in the dense phase we further find active-passive segregation,
with "rafts" of passive particles in a "sea" of active particles. We find that
phase separation from an initially disordered mixture can occur with as little
as 15 percent of the particles being active. Finally, we show that a system
prepared in a suitable fully segregated initial state reproducibly
self-assembles an active "corona" which triggers crystallization of the passive
core by initiating a compression wave. Our findings are relevant to the
experimental pursuit of directed self-assembly using active particles.
