A fine spherical particle formed of diamond as a core and having carbon nano-materials radially grown therefrom is disclosed, which exhibits the appearance of a Marimo (Cladophora sauteri) particle. Fine diamond catalytic particles 2 whose surfaces are oxidized and treated to carry a transition metal catalyst are floated and stirred in a gas phase of hydrocarbon while being heated at a selected temperature to bring about a catalytic reaction which synthesizes carbon nano-materials and to grow them on the surface of said oxidized fine diamond particle. Nano fibers or filaments 32 of a nano size are grown from the fine diamond catalytic particle 31 as a core to form cladophora-form carbon. The carbon nano-materials if the supported transition metal is Ni or Co become carbon nano-tubes and if it is Pd become coin stacked carbon nano-graphite.