Abstract: Microporous silicate tiettaite from the Khibiny alkaline massif (Kola Peninsula, Russia) has been studied using X-ray diffraction analysis, electron probe microanalysis, and Raman spectroscopy of single crystals and powders. Its chemical formula is refined to be K₄Na₁₂Fe³⁺Si₁₆O₄₁(OH)₄⋅ 2H₂O. The Raman spectrum of tiettaite contains lines at 3650, 3450, 1097, 1066, 980, 920, 681, 635, 569, 499, 458, 404, 272, 144 cm^–1. The orthorhombic unit-cell parameters are a = 28.866(7) Å, b = 10.707(3) Å, c = 17.425(7) Å, V = 5385(3) ų, Z = 4, sp. gr. Cmcm. The tiettaite crystal structure has been solved for the first time from single crystal and refined by the Rietveld method to the final R_wp = 2.47% and R_Bragg = 1.38%. The structure based on a new-type microporous heteropolyhedral framework formed by one-dimensional modules [Si₂₈Na₁₆Fe₄K₄O₁₁₀]^76– elongated along the c axis. Each module consists of complex ribbons with compositions of [Si₁₄O₃₉]^22– and [Fe₂K₂Na₆O₃₂]^50– compose a framework via shared vertices of half-occupied silicon–oxygen tetrahedra Si5 and Si6. Tiettaite structure contains a three-dimensional system of crossed channels with effective channel widths of 2.61 × 7.50, 2.46 × 2.92, and 3.60 × 3.90 Ų, running along the [100], [010], and [001] directions, respectively. The presence of a system of broad channels allows one to consider tiettaite as promising ion exchanger. Regarding the information complexity parameters, tiettaite can be assigned to minerals with very complex structure.