Kanemite was studied by single-crystal X-ray diffraction. The mineral, ideally NaHSi ₂ O ₅ .3H ₂ O, is orthorhombic (space group Pbcn); unit-cell parameters are a = 4.946(3), b = 20.502(15), c = 7.275(3) Aa, with Z = 4. The structure is solved and refined to an R value of 0.058 for 825 independent reflections. The arrangement of atoms consists of alternating (010) sheets of corrugated [Si ₂ O ₄ OH] (super n-) _n and hydrated Na. The silicate sheets contain six-membered rings of HOSiO ₃ -SiO ₄ units. Sodium atoms coordinate to six water molecules, forming layers of distorted octahedra. Residual electron densities were located that give reasonable positions for four H atoms. One H is part of a silanol group, and the other three H atoms are associated with water bonded to Na. Bonding between the silicate and Na sheets is through hydrogen bonding from H of the Na layer to O of the silicate sheet.

Here we report a nomenclature and classification for the seidozerite-supergroup minerals. The TS (Titanium-Silicate) block is the main structural unit in all seidozerite-supergroup structures; it consists of a central O (O = Octahedral) sheet and two adjacent H (H = Heteropolyhedral) sheets where Si₂O₇groups occur in the H sheets. The TS block is characterized by a planar minimal cell based on translation vectors, t₁and t₂, the lengths of these vectors are t1 ≈ 5.5 and t2 ≈ 7 Å, and t1 ^ t2 is close to 90°. The forty-five minerals of the sedozerite supergroup are divided into four groups based on the content of Ti and topology and stereochemistry of the TS block: in rinkite, bafertisite, lamprophyllite and murmanite groups, Ti (+ Nb + Zr + Fe³⁺+Mg + Mn) = 1, 2, 3 and 4 apfu (atoms per formula unit), respectively. All TS-block structures consist either solely of TS blocks or of two types of block: the TS block and an I (Intermediate) block that comprises atoms between two TS blocks. Usually, the I block consists of alkali and alkaline-earth cations, H₂O groups and oxyanions (PO₄)^3-, (SO₄)^2-and (CO₃)^2-.The general formula of the TS block is as follows A^P₂B^P₂M^H₂M^O₄(Si₂O₇)_2X4+n, where M^H₂and M^O₄= cations of the H and O sheets; MH = Ti, Nb, Zr, Y, Mn, Ca + REE, Ca;MO = Ti, Zr, Nb, Fe³⁺, Fe²⁺, Mg, Mn, Zn, Ca, Na; AP and BP = cations at the peripheral (P) sites = Na, Ca + REE, Ca, Zn, Ba, Sr, K; X = anions = O, OH, F, H₂O; X^O₄+n=X_O4 +X^P_n, n = 0, 1, 1.5, 2, 4; X^P= X^P_Mand X^P_A= apical anions of MH and AP cations at the periphery of the TS block.