The new mineral species ozerovaite was found in the fumarole of the second cinder cone of the Great Tolbachik Fissure Eruption. The colour of ozerovaite varies from colourless to pale yellow. It is insoluble in water. The mineral occurs as tabular crystals, 0.04 ☓ 0.02 ☓ 0.004 mm ³ average size; with aggregates of 0.02–0.3 mm. The empirical formula calculated on the basis of 16 O atoms per formula unit (apfu) is (Na _1.82 K _1.08 ) _∑2.90 (Al _2.62 Fe _0.32 Cu _0.12 Zn _0.02 ) _∑3.08 (As _3.95 P _0.07 ) _∑4.02 O ₁₆ , and the idealised formula is Na ₂ KAl ₃ (AsO ₄ ) ₄ . Ozerovaite is orthorhombic: Cmca, a = 10.615(2), b = 20.937(3), c = 6.393(1) Å, V = 1420.9(3) Å ³ , Z = 4. The crystal structure (R ₁ = 0.031) is constructed of AlO ₆ octahedra and AsO ₄ tetrahedra, linked by the corners and edges. Adjacent layers are held together by six-and four-coordinated Na and six-coordinated K polyhedra. The eight strongest diagnostic lines of the X-ray powder diffraction pattern are (I, d in Å, hkl]: 44, 10.37, 020; 47, 5.47, 200; 47, 4.84, 220; 17, 3.76, 240; 26, 3.07, 061; 83, 2.922, 260; 100, 2.824, 202; and 71, 2.735, 400. Ozerovaite is biaxial, optically negative, α (calc.) = 1.645, β = 1.667(2), γ = 1.674(2) (589 nm), 2V (meas.) = 58(10)°. Associated minerals are ponomarevite, piypite, dolerophanite, euchlorine, sylvite, lammerite, johillerite, urusovite, bradaczekite, filatovite, hatertite, hematite, tenorite and wrightite. The mineral is named in honour of the Russian scholar Dr. Nina Aleksandrovna Ozerova (1930–2012), for her contributions to geochemistry, geology, metallogeny, ecology and the eco-geochemistry of mercury.