Pulverulent compositions of a complex between an acid and a metal form an at least partially spherical particle. The acid is selected from 2-hydroxy-4-methyl-thiobutanoic acid (HMTBA), methionine, aspartic acid, the alginic acids, the pectinic acids, and the corresponding anions, in particular 2-hydroxy-4-methyl-thiobutanoate, methioninate, aspartate, the alginates and the pectinates. The metal is divalent or trivalent. The particle has an amorphous fraction the mass of which represents at least 50% of the total mass of the particle. The particle is substantially devoid of uncomplexed acid or anion and of uncomplexed metal or metal cation.