  Hard spheres with a polydispersity above approximately 8% are shown to
crystallise into two phase-separated solid phases. A polydispersity above 8% is
too large to be tolerated by a single solid phase but phase separation produces
two fractions with polydispersities sufficiently narrow to allow them to
crystallise. It may not be possible to observe this in experiment due to the
intervention of a glass transition.
