Stibivanite-2O, a new orthorhombic polytype of Sb2VO5, has been found at Buca della Vena mine. It occurs as emerald-green acicular and fibrous crystals in a vein of recrystallized dolomite. The space group of the mineral is Pmcn, with a 17.916(3), b 4.790(1), c 5.509(1) angstrom. The strongest lines (visual estimation) in the powder pattern [d in angstrom, intensity in parentheses] are: 3.097(s), 2.986(ms), 9.00 (m), 4.62(m), 1.871(ms), 1.747(mw). The OD character of the structure of monoclinic stibivanite has been established. On the basis of OD theory, a structural model for the orthorhombic modification is proposed. The model has been confirmed through a least-squares refinement, carried out with 530 observed reflections, to a final R of 0.032. The structure of stibivanite-2O, as well as that of the monoclinic polytype, is characterized by the presence of complex ribbons very weakly linked in a and b directions. In the complex ribbons, chains of corner-sharing SbO3 pyramids are attached to both sides of edge-sharing VO5 pyramids.