The new mineral eleomelanite, (K₂Pb)Cu₄O₂(SO₄)₄, was found in the Arsenatnaya fumarole on the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia. It is associated with euchlorine, fedotovite, wulffite, chalcocyanite, dolerophanite, dravertite, hermannjahnite, alumoklyuchevskite, klyuchevskite, piypite, cryptochalcite, cesiodymite, anglesite, langbeinite, calciolangbeinite, metathénardite, belomarinaite, aphthitalite, krasheninnikovite, steklite, anhydrite, hematite, tenorite, sanidine, sylvite, halite, lammerite, urusovite, and gold. Eleomelanite occurs as interrupted crusts up to 6 mm across and up to 0.3 mm thick consisting of equant, prismatic, or tabular crystals or grains up to 0.3 mm. It is translucent and black. The luster is oleaginous on crystal faces and vitreous on a cleavage surface. D_calc is 3.790 g/cm³. Eleomelanite is optically biaxial (-), a 1.646(3), b 1.715(6), c 1.734(6), 2V_meas. ¼ 60(15)8. The chemical composition (wt.%, electron-microprobe) is K₂O 9.62, Rb₂O 0.49, Cs₂O 0.24, CaO 1.23, CuO 35.28, PbO 19.25, SO₃ 34.78, total 100.89. The empirical formula calculated based on 18 O apfu is (K_1.88Pb_0.79Ca_0.20Rb_0.05Cs_0.02)_R2.94Cu_4.07S_3.99O₁₈. Eleomelanite is monoclinic, P2₁/n, a 9.3986(3), b 4.8911(1), c 18.2293(5) Å, b 104.409(3)8, V 811.63(4) ų, and Z ¼ 2. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 9:07ð63Þð 101Þ 7.38(44)(101), 3.699(78)(112), 3:658ð100Þð 204Þ, 3.173(40)(211), 2.915(35)(114), 2.838(35)(204), 2:683ð36Þð 215Þ, and 2:576ð51Þð310; 116Þ. The crystal structure was solved using single-crystal XRD data, R₁ ¼ 4.78%. It is based on heteropolyhedral Cu-S-O chains composed of Cu-centered polyhedra with [4þ1þ1] Cu^2þ coordination and SO₄ tetrahedra. Adjacent Cu-S-O chains are connected via chains of (K,Pb)O₈ and KO₁₀ polyhedra. Eleomelanite belongs to a novel structure type but has common structural features with klyuchevskite, alumoklyuchevskite, wulffite, parawulffite, and piypite. The name is derived from the Greek ekaiom (eleon), oil, and léka1 (melas), black, due to its black color and oleaginous luster on crystal faces that are uncommon for sulfate minerals.