Zaykovite, ideally Rh3Se4, is a new mineral, the first natural rhodium selenide. It was discovered in the assemblages of platinum-group minerals from the Kazan gold placer, South Urals, Russia. The mineral occurs as crystals up to 40 μm in size within the grains of Pt3Fe alloy, in association with unnamed Pd-Sb-Te phase and Au-Pd alloy. In reflected light, zaykovite has a gray color with bluish-greeenish tint; it shows weak bireflectance and anisotropy. Reflectance values [R _max/R _min(%) for COM approved wavelengths (nm)]: 30.1/29.3(470), 32.2/31.0(546), 33.4/32.0(589), 35.1/33.7(650). Chemical composition corresponds to the empirical formula (Rh _2.26Pt _0.46Ir _0.25Ru0.01Pd _0.01Fe _0.01)Σ3.00(Se _2.77S _1.21Te _0.02)Σ4.00 Zaykovite is monoclinic, space group C2/m, a 10.877(1), b 11.192(1), c 6.4796(6) Å, β 108.887(2)°, V 746.3(1) Å3, Z = 6, Dcalc 8.32 g cm-1. The crystal structure has been solved and refined to R1 = 0.016 based on 858 unique observed reflections. The strongest lines of the X-ray powder diffraction pattern [d(Å), (I), (hkl)] are: 5.43(37)(-111), 3.275(75)(310), 3.199(100)(-131), 3.061(87)(002), 2.568(62)(400), 2.545(41)(041), 3.413(34)(-241), 1.697(34)(441). Zaykovite is a Se analogue of kingstonite, Rh ₃S ₄. A continuous series of solid solutions between kingstonite and zaykovite was encountered in the assemblages of the Kazan placer. The possible sources of unique Rh-Se mineralization at South Urals could be serpentinised dunite-harzburgite or gabbro-clinopyroxenite-dunite complexes in the vicinity.