There are the Dwarf Planets; once you hit self-rounding to solid, you also start having a bit of concentration to the core of heavier elements.
The concentration processes are interesting, because some are gravitational/mechanical, while others are thermochemical.
Sulphur is concentrated by thermochemical - it's dissolved in hot water, and when the water hits surface and cools, the sulphur condenses out. Not going to happen on a dwarf.
But a dwarf planet might have a core... Ceres is expected to...
(Src:
Space.com)
Not as differentiated as larger worlds, but still, a core expected to be mixed (chemistry definition) metals and silicates (as opposed to Astronomers' definition of metal being anything higher than helium being, which even a snowball is 8/9 metal). And Ceres isn't all that large as far as Dwarf Planets go.
Plus, Ceres is expected to have an ocean layer; if it does, the thermochemical concentrations may happen.
If the core gets radioactives, the core may be more consolidated than size would otherwise indicate. And might also drive a good bit more thermochemical concentration.
it is possible that some asteroid belts may have remnants of shattered dwarf planets or even proper planets; there's not enough mass in ours to represent that, but it's also possible Ceres is still slowly clearing its orbit... or might have an untimely impact and cease to be a dwarf planet...