Ponomarevite is one of the principal minerals of Recent exhalation ore shows on the cones of the Great Tolbachik Fissure Eruption of 1975-76. Interpreting its crystal structure helps to identify the forms of transport of the ore components, particularly copper, in volcanic gases. The crystal-chemical formula of the specimen that we studied is (K_3.53Na_0.49)_Σ4.02 (Cu_3.97Zn_0.03)_Σ4.00O_1.10Cl_9.82. The structure of ponomarevite is based on the tetrahedral cluster [Cu₄OCl₁₀]^4-. The copper is in fivefold coordination (4Cl + θ). The chlorine atoms form a tetrahedron, three of them participating in bridge bonds and one acting as an end atom. Overall, the structure may be classified as the island type with the [Cu₄OCl₁₀]^4- complex acting as the island; this is apparently the form in which copper is transported in volcanic gases. Thus, interpretation of the crystal structure of ponomarevite provides information for genetic mineralogy and helps to identify the conditions of its generation from the gaseous phase.