Ferromagnetic particulate matter from various volcanic areas has been compared with black magnetic spherules (b.m.s.) sampled in air and in marine sediments. The following main differences have been recognized: (1) in the volcanic ash deposits, ferromagnetic spherules neither solid nor hollow are found; only magnetite crystals usually associated with silicate fragments have been observed; (2) the volcanic ferromagnetic particles and the b.m.s. have similar Fe contents but different contents of minor elements, the former yielding Si, Al, Ti, Ca, Mg, and Cr, and the latter, Ni, Co, and Ir; and (3) while the b.m.s. have a polycrystalline structure characterized by a magnetite, w¿stite, and α-Fe paragenesis, the volcanic particles are composed only of magnetite and are often in monocrystalline form. Thermodynamic considerations agree with the experimental results showing that the b.m.s. cannot have a volcanic origin.