The new zeolite-like titanosilicate mineral kamenevite K2TiSi3O9·H2O, isostructural with umbite K2ZrSi3O9·H2O, is found in two peralkaline pegmatites located at Mt. Suoluaiv (Oleniy Ruchey mine: holotype) and Mt. Rasvumchorr (Rasvumchorr mine) in the Khibiny alkaline complex, Kola peninsula, Russia. It is a hydrothermal mineral associated with lomonosovite, aegirine, villiaumite, pectolite, shafranovskite, ershovite, umbite, potassic feldspar, sodalite, lamprophyllite, etc. Kamenevite occurs as lamellar crystals up to 0.02 × 0.1 × 0.3 mm and their aggregates up to 0.7 mm (Oleniy Ruchey) or grains up to 0.15 mm across (Rasvumchorr). The mineral is transparent, colourless (white in aggregates), with vitreous lustre. It is brittle, the Mohs hardness is ca. 4. Cleavage is (010) good. Dmeas = 2.69(2), Dcalc = 2.698 g cm−3. Kamenevite is optically biaxial (–), α = 1.650(4), β = 1.678(5), γ = 1.685(5), 2Vmeas = 60(10)°. The chemical composition of the holotype [wt%, electron microprobe data, H2O content calculated for 1 (H2O) pfu] is: Na2O = 0.48, K2O = 24.37, CaO = 0.13, Fe2O3 = 0.35, SiO2 = 48.78, TiO2 = 20.30, ZrO2 = 0.89, Nb2O5 = 0.35, H2O = 4.85, total = 100.50. The empirical formula calculated on the basis of 10 O atoms per formula unit (apfu) is (K1.92Na0.06Ca0.01)Σ1.99(Ti0.94Zr0.03Fe0.02Nb0.01)Σ1.00S3.01O9·H2O. Kamenevite is orthorhombic, P212121, a = 9.9166(4), b = 12.9561(5), c = 7.1374(3) Å, V = 917.02(6) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.92(70)(110), 6.51(47)(020), 5.823(95)(101), 2.988(84)(301, 122), 2.954(100)(041, 320), 2.906(68)(311, 202) and 2.834(69)(141, 212). The crystal structure (single-crystal XRD data, R = 0.0384) is based on a microporous heteropolyhedral framework built by [Si3O9] wollastonite-type chains linked by isolated Ti-centred octahedra. The K+ cations and H2O molecules are located in wide and narrower [001] channels. The mineral is named in honour of the outstanding Russian geologist Evgeniy Arsenievich Kamenev (1934–2017) who made great contribution to the geology of the Khibiny complex.

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