A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn0.98Fe0.02)Σ1.00Sb2.00O6; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (ncalc is 2.38 at 589 nm); Dobs 6.66 g/cm3, Dcalc 6.67 g/cm3. It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P42/mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.