A new light weight particulate material is provided which comprises fruit (cherry) stones, or pits, stabilized against germination, weathering and general degradation caused by chemical or biological attack. Stabilization of the stones is accomplished by heat treatment alone or by heat treatment plus sealing of any openings in them. The stabilized stones are useful as a structural material, as a filler in solid syntactic composites, and as the primary component in tactic (open pore) composites. The loose stabilized stones can be used in applications such as "bean bags".