Density functional theory study and kinetic analysis of the formation mechanism of Al30O8(OH)56(H2O)26 (Al30) in aqueous solution

The formation mechanism of Al₃₀O₈(OH)₅₆(H₂O)₂₆¹⁸⁺ (Al₃₀) has been investigated by the density functional theory based on the supermolecule model and kinetic analysis on the ²⁷Al nuclear magnetic resonance (NMR) experimental results in monitoring Al₃₀ synthesis process. The theoretical chemistry calculations on the four possible schemes show that δ-Na-Al₁₃ is the reasonable intermediate followed by the substitution of Na with Al to form δ-Al₁₄, and Na⁺ plays an important role in stabilizing the intermediate (δ-Na-Al₁₃) in the transformation. The kinetic analysis on the ²⁷Al NMR experimental data indicates that ε-Al₁₃ decomposes and isomerizes in the formation of Al₃₀, while Al monomers facilitate the decomposition of ε-Al₁₃ and so the isomerization of ε-isomers to δ-isomers effectively. The favorable formation mechanism of Al₃₀ includes three steps: (1) ε-Al₁₃ decomposes and rearranges into the isomer δ-Al₁₃; (2) Na⁺ reacts with δ-Al₁₃ to stabilize the intermediate δ-Na-Al₁₃, followed by Al monomers replacing Na to form δ-Al₁₄; (3) δ-Al₁₄ reacts with the Al monomers in the solution to finally form Al₃₀. Both Al monomers and Na⁺ are important in the transformation. Al monomers are the basic building units and helpful to the isomerization while Na⁺ can well stabilize the isomer δ-Al₁₃ to yield intermediate δ-Na-Al₁₃. The results also show that other isomers of ε-Al₁₃ (β-Al₁₃ and α-Al₁₃) form in the formation of Al₃₀, and their calculated ²⁷Al NMR tetrahedral resonance shifts are consistent with the experimental ²⁷Al NMR tetrahedral signals in the preparation process of Al₃₀.     

Rates of oxygen exchange between the Al2O8Al28(OH)56(H2O)26(aq) (Al30) molecule and aqueous solution

Rates of steady exchange of oxygens between bulk solution and the largest known aluminum polyoxocation: Al₂O₈Al₂₈(OH)₅₆(H₂O)₂₆¹⁸⁺(aq) (Al₃₀) are reported at pH≈4.7 and 32-40°C. The Al₃₀ molecule is a useful model for geochemists because it is ≈2 nm in length, comparable to the smallest colloidal solids, and it has structural complexity greater than the surfaces of most aluminum (hydr)oxide minerals. The Al₃₀ molecule has 15 distinct hydroxyl sites and eight symmetrically distinct bound waters. Among the hydroxyl bridges are two sets of μ₃-OH, which are not present in any of the other aluminum polyoxocations that have yet been studied by NMR methods. Rates of isotopic equilibration of the μ₂-OH and μ₃-OH hydroxyls and bound water molecules fall within the same range as we have determined for other aluminum solutes, although it is impossible to determine rate laws for exchange at the large number of individual oxygen sites. After injection of ¹⁷O-enriched water, growth of the ¹⁷O-NMR peak near 37 ppm, which is assigned to μ₂-OH and μ₃-OH hydroxyl bridges, indicates that these bridges equilibrate within two weeks at temperatures near 35°C. The peak at +22 ppm in the ¹⁷O-NMR spectra, assigned to bound water molecules (η-OH₂), varies in width with temperature in a similar fashion as for other aluminum solutes, suggesting that most of the η-OH₂ sites exchange with bulk solution at rates that fall within the range observed for other aluminum complexes. Signal from one anomalous group of four η-OH₂ sites is not observed, indicating that these sites exchange at least a factor of ten more rapidly than the other η-OH₂ sites on the Al₃₀.     

Acid dissociation mechanisms of Si(OH)4 and Al(H2O)6 in aqueous solution

Silicic acid and the hexa-aqua of Al³⁺ are fundamental model aqueous species of chemical importance in nature. In order to investigate their hydroxyl dissociation mechanisms, Car-Parrinello molecular dynamics (CPMD) simulations were carried out, which allow treating the solutes and solvents on the same footing. The method of constraint was employed to trigger the reactions by taking coordination number as the reaction coordinate and the thermodynamic integration was used to obtain the free-energy profiles. The approximate transition states were located and the reactant and product states were also characterized. The free-energy changes of dissociation are found about 15.0 kcal/mol and 7.7 kcal/mol for silicic acid and Al-aqua, respectively. From the simulation results, the first pKas were calculated by using two approaches, which are based on the pristine thermodynamic relation and the RDF (radial distribution function)-free energy relation, respectively. Because of more uncertainties involved in the RDF way, it is suggested that the pristine way should be favored, which shows an error margin of 1 pKa unit. This study provides an encouraging basis for applying the present methodology to predict acidity constants of those groups that are difficult to measure experimentally.     

Theoretical exploration of the water exchange mechanism of the polyoxocation GaO4Al12(OH)24(H2O)12 in aqueous solution

Reaction pathways, solvent effects and energy barriers have been investigated for the water exchange of the polyoxocation GaO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁺ (K-GaAl₁₂) in aqueous solution by means of supermolecule density functional theory calculations. In the proposed reaction pathway, the supermolecular reactant K-GaAl₁₂15H₂O first loses a water ligand to form an intermediate with a five-coordinated aluminum atom, and then the incoming water molecule in the second coordination sphere attacks the intermediate with a five-coordinated aluminum atom to produce the reaction product. Our calculated results indicate that the water exchange of K-GaAl₁₂ proceeds via a dissociative mechanism, and that the reverse reaction of Step II is the most favorable dissociative pathway, with a barrier height of 31.3 kJ mol⁻¹. The calculated transition-state rate for the favorable dissociative pathway is much larger than the experimental rate constant, but is close to the data calculated for Al₃₀ by molecular dynamics. The transmission coefficient was also predicted on the basis of both the calculated transition-state rate and the experimental rate. Our calculated results also indicate that both the explicit solvent effect and the bulk solvent effect have obvious effects on the barrier heights of the water exchange reaction of K-GaAl₁₂. By comparison, the water exchange mechanism for K-GaAl₁₂ was found to be more similar to that for mineral surfaces than that for monomeric aluminum species.     

Solubility of Fe-ettringite (Ca6[Fe(OH)6]2(SO4)3 · 26H2O)

The solubility of Fe-ettringite (Ca₆[Fe(OH)₆]₂(SO₄)₃ · 26H₂O) was measured in a series of precipitation and dissolution experiments at 20 °C and at pH-values between 11.0 and 14.0 using synthesised material. A time-series study showed that equilibrium was reached within 180 days of ageing. After equilibrating, the solid phases were analysed by XRD and TGA while the aqueous solutions were analysed by ICP-OES (calcium, sulphur) and ICP-MS (iron). Fe-ettringite was found to be stable up to pH 13.0. At higher pH-values Fe-monosulphate (Ca₄[Fe(OH)₆]₂(SO₄) · 6H₂O) and Fe-monocarbonate (Ca₄[Fe(OH)₆]₂(CO₃) · 6H₂O) are formed. The solubilities of these hydrates at 25 °C are:      

La sénégalite,Al2 (PO4) (OH)3 · H2O,un nouveau minéral

Senegalite is orthorhombic, mm2, a:b:c:=1.296:1:1.007; $\text{a}{}_0\text{=9.673,}\text{b}{}_0\text{=7.596,}\text{c}{}_0\text{=7.668}\text{A}\text{?}$, Z=4, G_calc=2551; space group Pna2. The strongest lines in the powder pattern are: 5.41(7); 4.089(9); 3.834(10); 3.610(8); 2.990(9); 2.348(8); 2.070(7) 1.929(7); 1.505(7) Å. The chemical analysis: Al₂O₃ ? 46.23; Fe₂O₃ ? 0.28; P₂O₅ ? 31.85 H₂O ? 21.00; sum 99.34, gives a formula Al₂(PO₄)(OH)₃ · H₂O. Colourless optically biaxial positive, n_S: α=1.562, β=1.566, γ=1.587, plane of optical axies (001), Z=a, Y=c; 2V=53°, weak dispersion r > v. Measured density 2.552. The DTA curve shows endothermic reactions at 250, 370 and 440°C corresponding to the dehydration of mineral. Infrared spectrum indicates the presence of OH and H₂O groups. Found in oxidation zone of Kouroudiako iron deposit, Senegal, associated with turquoise, augelite, wavellite and crandallite.     

Solid-liquid equilibria of Mg(OH)2(cr) and Mg2(OH)3Cl·4H2O(cr) in the system Mg-Na-H-OH-Cl-H2O at 25°C

The solubility of crystalline Mg(OH)₂(cr) was determined by measuring the equilibrium H⁺ concentration in water, 0.01-2.7 m MgCl₂, 0.1-5.6 m NaCl, and in mixtures of 0.5 and 5.0 m NaCl containing 0.01-0.05 m MgCl₂. In MgCl₂ solutions above 2 molal, magnesium hydroxide converted into hydrated magnesium oxychloride. The solid-liquid equilibrium of Mg₂(OH)₃Cl·4H₂O(cr) was studied in 2.1-5.2 m MgCl₂. Using known ion interaction Pitzer coefficients for the system Mg-Na-H-OH-Cl-H₂O (25°C), the following equilibrium constants at I = 0 are calculated:

     

Residence times for protons bound to three oxygen sites in the AlO4Al12(OH)24(H2O)12 polyoxocation

Although, the kinetic reactivity of a mineral surface is determined, in part, by the rates of exchange of surface-bound oxygens and protons with bulk solution, there are no elementary rate data for minerals. However, such kinetic measurements can be made on dissolved polynuclear clusters, and here we report lifetimes for protons bound to three oxygen sites on the AlO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁺ (Al₁₃) molecule, which is a model for aluminum-hydroxide solids in water. Proton lifetimes were measured using ¹H NMR at pH ∼ 5 in both aqueous and mixed solvents. The ¹H NMR peak for protons on bound waters (η-H₂O) lies near 8 ppm in a 2.5:1 mixture of H₂O/acetone-d₆ and broadens over the temperature range −20 to −5 °C. Extrapolated to 298 K, the lifetime of a proton on a η-H₂O is τ²⁹⁸ ∼ 0.0002 s, which is surprisingly close to the lifetime of an oxygen in the η-H₂O (∼0.0009 s), but in the same general range as lifetimes for protons on fully protonated monomer ions of trivalent metals (e.g., Al(H₂O)₆³⁺). The lifetime is reduced somewhat by acid addition, indicating that there is a contribution from the partly deprotonated Al₁₃ molecule in addition to the fully protonated Al₁₃ at self-buffered pH conditions. Proton lifetimes on the two distinct sets of hydroxyls bridging two Al(III) (μ₂-OH) differ substantially and are much shorter than the lifetime of an oxygen at these sites. The average lifetimes for hydroxyl protons were measured in a 2:1 mixture of H₂O/dmso-d₆ over the temperature range 3.7-95.2 °C. The lifetime of a hydrogen on one of the μ₂-OH was also measured in D₂O. The τ²⁹⁸ values are ∼0.013 and ∼0.2 s in the H₂O/dmso-d₆ solution and the τ²⁹⁸ value for the μ₂-OH detectable in D₂O is τ²⁹⁸ ∼ 0.013 s. The ¹H NMR peak for the more reactive μ₂-OH broadens slightly with acid addition, indicating a contribution from an exchange pathway that involves a proton or hydronium ion. These data indicate that surface protons on minerals will equilibrate with near-surface waters on the diffusional time scale.     

Theoretical investigation of iron isotope fractionation between Fe(H2O)6 and Fe(H2O)6: Implications for iron stable isotope geochemistry

The magnitude of equilibrium iron isotope fractionation between Fe(H₂O)₆³⁺ and Fe(H₂O)₆²⁺ is calculated using density functional theory (DFT) and compared to prior theoretical and experimental results. DFT is a quantum chemical approach that permits a priori estimation of all vibrational modes and frequencies of these complexes and the effects of isotopic substitution. This information is used to calculate reduced partition function ratios of the complexes (10³ · ln(β)), and hence, the equilibrium isotope fractionation factor (10³ · ln(α)). Solvent effects are considered using the polarization continuum model (PCM). DFT calculations predict fractionations of several per mil in ⁵⁶Fe/⁵⁴Fe favoring partitioning of heavy isotopes in the ferric complex. Quantitatively, 10³ · ln(α) predicted at 22°C, ∼ 3 ‰, agrees with experimental determinations but is roughly half the size predicted by prior theoretical results using the Modified Urey-Bradley Force Field (MUBFF) model. Similar comparisons are seen at other temperatures. MUBFF makes a number of simplifying assumptions about molecular geometry and requires as input IR spectroscopic data. The difference between DFT and MUBFF results is primarily due to the difference between the DFT-predicted frequency for the ν₄ mode (O-Fe-O deformation) of Fe(H₂O)₆³⁺ and spectroscopic determinations of this frequency used as input for MUBFF models (185-190 cm⁻¹ vs. 304 cm⁻¹, respectively). Hence, DFT-PCM estimates of 10³ · ln(β) for this complex are ∼ 20% smaller than MUBFF estimates. The DFT derived values can be used to refine predictions of equilibrium fractionation between ferric minerals and dissolved ferric iron, important for the interpretation of Fe isotope variations in ancient sediments. Our findings increase confidence in experimental determinations of the Fe(H₂O)₆³⁺ − Fe(H₂O)₆²⁺ fractionation factor and demonstrate the utility of DFT for applications in “heavy” stable isotope geochemistry.     

Activation volumes for oxygen exchange between the GaO4Al12(OH)24(H2O)127+(aq) (GaAl12) polyoxocation and aqueous solution from variable pressure O NMR spectroscopy

Activation volumes for exchange of oxygen between bulk aqueous solution and sites in the GaO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁺(aq) (GaAl₁₂) complex were measured by variable-pressure ¹⁷O NMR techniques. Near 322 K, rates of exchange for the less labile set of bridging hydroxyls in the GaAl₁₂ decrease by a factor of about two with increasing pressure from 0.1 to 350 MPa. These data indicate a substantially positive activation volume of ΔV^‡ = +7 ± 1 cm³/mol, which is the first activation volume measured for a bridging hydroxyl in a polynuclear complex. This result suggests significant bond-lengthening in the activation step. Electrostriction effects should be small because exchange occurs via a pH-independent path under the experimental conditions. The second, more labile set of bridging hydroxyls exchange too rapidly for the variable-pressure techniques employed here. The exchange of bound-water molecules on the GaAl₁₂ was observed at P = 350 MPa using the ¹⁷O-NMR line-broadening technique. Comparison with previous measurements at 0.1 MPa indicates decreasing line width from 0.1 to 350 MPa for temperatures at which exchange dominates, yielding an activation volume of ΔV^‡ = +3(± 1) cm³/mol. This activation volume is smaller than the value for the Al(H₂O)₆³⁺ complex, suggesting that water exchange on the larger GaAl₁₂ complex has less dissociative character although the average charge density is lower.     

Structural change and mineralogical transformation mechanism of aluminum hydroxide gels from forced hydrolysis Al（Ⅲ） solutions containing AlO4Al12（OH）24（H2O）12^7＋ polyoxycation during aging

The structural change and mineralogy of Al gel during aging time were investigated by using spectroscopy techniques. The results indicated that: 1) the aggregation extent of solution-gel system increases with aging time, and the structure of amorphous gel becomes more short-ordered; 2) after six months, the gel formats nordstrandite and little gibbsite; 3) a marked decrease in the number of (Al-OH)_oh bands occurring at 610 cm⁻¹ and increase in the number of (Al-OH₂)_oh bands occurring at 555 cm⁻¹ indicate that the gel undergoes rearrangement-like process during aging; 4) the gel constantly contains Al-O tetrahedron of Keggin structure, but the signal peak occurring at ≈61×10⁻⁶ of ²⁷Al MAS NMR have a slight shift to downfield with aging time. A mineralogical transformation mechanism for hydrolysis Al(III) solution was proposed.     

Mineral-solution equilibria—III. The system Na2OAl2O3SiO2H2OHCl

Chemical equilibrium between sodium-aluminum silicate minerals and chloride bearing fluid has been experimentally determined in the range 500–700°C at 1 kbar, using rapid-quench hydrothermal methods and two modifications of the Ag + AgCl acid buffer technique. The temperature dependence of the thermodynamic equilibrium constant (K) for the reaction $\text{NaAlSi}{}_3\text{O}{}_8\text{+ HCl}{}^{\mathrm{o}}\text{= NaCl}{}^{\mathrm{o}}\text{+}\text{1}\text{2Al}{}_2\text{SiO}{}_5\text{, +}\text{5}\text{2SiO}{}_2\text{+}\text{1}\text{2H}{}_2\text{O}$ Albite Andalusite Qtz. can be described by the following equation: log k = ?4.437 + 5205.6/T(K) The data from this study are consistent with experimental results reported by Montoya and Hemley (1975) for lower temperature equilibria defined by the assemblages albite + paragonite + quartz + fluid and paragonite + andalusite + quartz + fluid. Values of the equilibrium constants for the above reactions were used to estimate the difference in Gibbs free energy of formation between NaCl^o and HCl^o in the range 400–700°C and 1–2 kbar. Similar calculations using data from phase equilibrium studies reported in the literature were made to determine the difference in Gibbs free energy of formation between KCl^o and HCl^o. These data permit modelling of the chemical interaction between muscovite + kspar + paragonite + albite + quartz assemblages and chloride-bearing hydrothermal fluids.     

Stable boron isotope fractionation between dissolved B(OH)3 and B(OH)4

The stable boron isotope ratio (¹¹B/¹⁰B) in marine carbonates is used as a paleo-pH recorder and is one of the most promising paleo-carbonate chemistry proxies. Understanding the thermodynamic basis of the proxy is of fundamental importance, including knowledge on the equilibrium fractionation factor between dissolved boric acid, B(OH)₃, and borate ion, B(OH)₄⁻ (, hereafter α_(B3-B4)). However, this factor has hitherto not been determined experimentally and a theoretically calculated value (Kakihana and Kotaka, 1977, hereafter KK77) has therefore been widely used. I examine the calculations underlying this value. Using the same spectroscopic data and methods as KK77, I calculate the same α_(B3−B4) = 1.0193 at 300 K. Unfortunately, it turns out that in general the result is sensitive to the experimentally determined vibrational frequencies and the theoretical methods used to calculate the molecular forces. Using analytical techniques and ab initio molecular orbital theory, the outcome for α_(B3-B4) varies between ∼1.020 and ∼1.050 at 300 K. However, several arguments suggest that α_(B3-B4) ? 1.030. Measured isotopic shifts in various ¹⁰B-, ²D-, and ¹⁸O-labeled isotopomers do not provide a constraint on stable boron isotope fractionation. I conclude that in order to anchor the fundamentals of the boron pH proxy, experimental work is required. The critics of the boron pH proxy should note, however, that uncertainties in α_(B3-B4) do not bias pH reconstructions provided that organism-specific calibrations are used.     

The kinetics of oxygen exchange between the GeO4Al12(OH)24(OH2)12(aq) molecule and aqueous solutions

We report rates of oxygen exchange with bulk solution for an aqueous complex, ^IVGeO₄Al₁₂(OH)₂₄(OH₂)₁₂⁸⁺(aq) (GeAl₁₂), that is similar in structure to both the ^IVAlO₄Al₁₂(OH)₂₄(OH₂)₁₂⁷⁺(aq) (Al₁₃) and ^IVGaO₄Al₁₂(OH)₂₄(OH₂)₁₂⁷⁺(aq) (GaAl₁₂) molecules studied previously. All of these molecules have ε-Keggin-like structures, but in the GeAl₁₂ molecule, occupancy of the central tetrahedral metal site by Ge(IV) results in a molecular charge of +8, rather than +7, as in the Al₁₃ and GaAl₁₂. Rates of exchange between oxygen sites in this molecule and bulk solution were measured over a temperature range of 274.5 to 289.5 K and 2.95 < pH < 4.58 using ¹⁷O-NMR.Apparent rate parameters for exchange of the bound water molecules (η-OH₂) are k_ex²⁹⁸ = 200 (±100) s⁻¹, ΔH^‡ = 46 (±8) kJ · mol⁻¹, and ΔS^‡ = −46 (±24) J · mol⁻¹ K⁻¹ and are similar to those we measured previously for the GaAl₁₂ and Al₁₃ complexes. In contrast to the Al₁₃ and GaAl₁₂ molecules, we observe a small but significant pH dependence on rates of solvolysis that is not yet fully constrained and that indicates a contribution from the partly deprotonated GeAl₁₂ species.The two topologically distinct μ₂-OH sites in the GeAl₁₂ molecule exchange at greatly differing rates. The more labile set of μ₂-OH sites in the GeAl₁₂ molecule exchange at a rate that is faster than can be measured by the ¹⁷O-NMR isotopic-equilibration technique. The second set of μ₂-OH sites have rate parameters of k_ex²⁹⁸ = 6.6 (±0.2) · 10⁻⁴ s⁻¹, ΔH^‡ = 82 (±2) kJ · mol⁻¹, and ΔS^‡ = −29 (±7) J · mol⁻¹ · K⁻¹, corresponding to exchanges ≈40 and ≈1550 times, respectively, more rapid than the less labile μ₂-OH sites in the Al₁₃ and GaAl₁₂ molecules. We find evidence of nearly first-order pH dependence on the rate of exchange of this μ₂-OH site with bulk solution for the GeAl₁₂ molecule, which contrasts with Al₁₃ and GaAl₁₂ molecules.     

K-H3OFe3(SO4)2(OH)6铁矾的XRD研究

根据X射线衍射(XRD)分析发现: A Fe₃(SO₄)₂(OH)₆(A=K⁺、H₃O⁺)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K⁺含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K⁺含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K⁺、H₃O⁺离子位于较大空隙中,且沿着Z轴方向排列,当K⁺、H₃O⁺离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。     

Dualite, Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9, a new zircono-titanosilicate with a modular eudialyte-like structure from the Lovozero alkaline Pluton, Kola Peninsula, Russia

Dualite has been found at Mount Alluaiv, the Lovozero Pluton, the Kola Peninsula in peralkaline pegmatoid as sporadic, irregularly shaped grains up to 0.3–0.5 mm across. K-Na feldspar, nepheline, sodalite, cancrinite, aegirine, alkaline amphibole, eudialyte, lovozerite, lomonosovite, vuonnemite, lamprophyllite, sphalerite, and villiaumite are associated minerals. Dualite is yellow, transparent or translucent, with conchoidal fracture. The new mineral is brittle, with vitreous luster and white streaks. The Mohs hardness is 5. The measured density is 2.84(3) g/cm₃ (volumetric method); the calculated density is 2.814 g/cm₃. Dualite dissolves and gelates in acid at room temperature. It is nonfluorescent. The new mineral is optically uniaxial and positive; ω = 1.610(1), ɛ = 1.613(1). Dualite is trigonal, space group R3m. The unit cell dimensions are a = 14.153(9), c = 60.72(5) ?, V = 10533(22) ?, Z = 3. The strongest reflections in the X-ray powder pattern [d, ? (I,%)(hkl)] are as follows: 7.11(40)(110), 4.31(50)(0.2.10), 2.964(100)(1.3.10), 2.839(90)(048), 2.159(60)(2.4.10, 0.4.20), 1.770(60)(2.4.22, 4.0.28, 440), 1362(50)(5.5.12, 3.0.42). The chemical composition (electron microprobe, H₂O calculated from X-ray diffraction data) is as follows, wt %: 17.74 Na₂O, 0.08 K₂O, 8.03 CaO, 1.37 SrO, 0.29 BaO, 2.58 MnO, 1.04 FeO, 0.79 La₂O₃, 1.84 C₂O₃, 0.88 Nd₂O₃, 0.20 Al₂O₃, 51.26 SiO₂, 4.40 TiO₂, 5.39 ZrO₂, 1.94 Nb₂O₅, 0.58 Cl, 1.39 H₂O,-O = 0.13 Cl₂; they total is 99.67. The empirical formula calculated on the basis of 106 cations as determined by crystal structure is (Na_29.79Ba_0.1K_0.10)_Σ30(Ca_8.55Na_1.39REE_1.27Sr_0.79)_Σ12 · (Na_3.01Mn_1.35Fe_0.87²⁺Ti_0.77)_Σ6(Zr_2.61Nb_0.39)_Σ3 (Ti_2.52Nb_0.48)_Σ3(Mn_0.82Si_0.18)_Σ1(Si_50.77Al_0.23)_Σ51 O₁₄₄[(OH)_6.54(H₂O)_1.34·Cl_0.98]_Σ8.86). The simplified formula is Na₃₀(Ca,Na,Ce,Sr)₁₂(Na,Mn,Fe,Ti)₆Zr₃Ti₃ MnSi₅₁O₁₄₄ (OH,H₂O,Cl)₉). The name dualite is derived from Latin dualis (dual) alluding to the dual taxonomic membership of this mineral, which is at the same time zirconosilicate and titanosilicate. The crystal structure is characterized by two module types (alluivite-like and eudialyte-like) alternating along a threefold axis with a doubled c period relative to eudialyte and close chemical affinity to rastsvetaevite (Khomyakov et al., 2006a) and labyrynthite (Khomyakov et al., 2006b). According to the authors’ crystal chemical taxonomy of the eudialyte group, the new mineral belongs to one of three subgroups characterized by a 24-layered structural framework. Dualite is a mineral formed during the final stages of peralkaline pegmatite formation. The type material of dualite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? A.P. Khomyakov, G.N. Nechelyustov, R.K. Rastsvetaeva, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, Pt CXXXVI, No. 4, pp. 68–73. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 8, 2005.