Kalyuzhnyite-(Ce), NaKCaSrCeTi(Si8O21)OF(H2O)3, a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan: mineral description, crystal structure and a new double (Si8O21) sheet

Abstract Kalyuzhnyite-(Ce), ideally NaKCaSrCeTi(Si8O21)OF(H2O)3, is a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan. It occurs as equant grains up to 0.05 × 0.07 mm in a quartz–pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and Dcalc. is 3.120 g/cm3. Kalyuzhnyite-(Ce) is monoclinic, P2/c, a = 18.647(4), b = 11.214(2), c = 14.642(3) Å, β = 129.55(3)° and V = 2360.9(11) Å3. The chemical composition of kalyuzhnyite-(Ce) is Nb2O5 0.53, TiO2 0.16, SiO2 43.85, Er2O3 0.13, Ho2O3 0.10, Gd2O3 0.09, Sm2O3 0.47, Nd2O3 6.22, Pr2O3 1.21, Ce2O3 6.34, La2O3 0.82, PbO 4.90, BaO 0.85, SrO 11.39, CaO 1.86, Cs2O 3.80, K2O 1.59, Na2O 2.99, H2O 5.24, F 1.55, O = F –0.65, total 100.31 wt.%. The empirical formula calculated on 26.11 (O + F) apfu is Na1.07K0.37Cs0.30Sr1.21Ca0.37Pb0.24Ba0.06(Ce0.43Nd0.41Pr0.08La0.06Sm0.03Gd0.01Er0.01Ho0.01)Σ1.04(Ti0.97Nb0.04)Σ1.01Si8.06O25.21F0.90H6.42, Z = 4. The simplified formula is (Na,□)(K,Сs)(Ca,Pb,Sr,Na)SrLn3+Ti(Si8O21)OF(H2O)3, where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R1 index of 2.74%. In kalyuzhnyite-(Ce), the main structural units are a heteropolyhedral Na–Sr–Ce–Ti sheet, ideally [NaSrCeTiOF]7+, and a double (Si8O21)10– sheet parallel to (010). In the Si–O sheet, the Si tetrahedra form ten-membered rings. This is the first occurrence of such a double Si–O sheet in a mineral. The two sheets connect via common vertices of Na-, Sr-, Ce- and Ti-polyhedra and SiO4 tetrahedra to form a framework. The interstitial cations and H2O groups, ideally [(CaK)(H2O)3]3+, occur within the Si–O sheet. The mineral is named in honour of Vasily Avksentievich Kalyuzhny (1899–1993) in recognition of his contributions to the geology of ore deposits of Komi Republic (USSR) and the mineralogy of granitic pegmatites (Tajikistan).


Introduction
This paper reports the description and the crystal structure of kalyuzhnyite-(Ce) [Russian Cyrillic: калюжныит-(Ce)], ideally NaKCaSrCeTi(Si 8 O 21 )OF(H 2 O) 3 , a new mineral from the wellknown Darai-Pioz alkaline massif, Tien-Shan Mountains, Central Tajikistan.Kalyuzhnyite-(Ce) is a sheet-silicate mineral with large channels and can potentially be used as a model for synthesis of microporous materials of industrial interest.Singlecrystal X-ray diffraction revealed a double Si 8 O 21 sheet of tenmembered rings of SiO 4 tetrahedra that has never been described in minerals (Hawthorne et al., 2019).The name is in honour of Vasily Avksentievich Kalyuzhny (Russian Cyrillic: Василий Авксентьевич Калюжный) (1899-1993), a prominent Russian geologist, an authority on the geology of the Komi Republic and its ore deposits; his pioneering work resulted in the discovery of the Yaregskoe Ti-deposit in oil-bearing sandstones of the Komi Republic.Dr. Kalyuzhny was also a member of the Pamir-Tajik geological expedition (1934)(1935)(1936)(1937), and he studied granite pegmatites of the Turkestan ridge around rivers of the Karavshin system and Sn-bearing pegmatites of the Kalbinsky ridge in Kazakhstan.The new mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association (IMA2022-133, Agakhanov et al., 2023).The holotype material is deposited in the systematic collection of the Fersman Mineralogical Museum, Moscow, Russia, catalogue number 98144.The IMA mineral symbol is Kalu-Ce.

Occurrence and associated minerals
Kalyuzhnyite-(Ce) occurs in the moraine of the Darai-Pioz glacier in the upper reaches of the Darai-Pioz River, Tien-Shan mountains, near the junction of the Turkestansky, Zeravshansky and Alaisky ridges (39°30 ′ N 70°40 ′ E).This area is in the Rasht (formerly Garm) district, Central Tajikistan.The Darai-Pioz alkaline massif belongs to the Upper Paleozoic Alaysky (Matchaisky) intrusive complex.Information on the geology of the Darai-Pioz massif can be found in Pautov et al. (2019) with reference to relevant earlier publications.Kalyuzhnyite-(Ce) was found in boulders (up to 2 m across) of quartz rock, i.e. silexite boulders composed of 90-95% medium-to coarse-grained quartz of ice-like appearance (quartz grains vary from 2 mm to 2 cm) characteristic for moraine deposits of the Darai-Pioz glacier.The following minor and accessory minerals are present: large (up to 10 cm across) golden-brown tabular and lamellar crystals of polylithionite, pink plates of sogdianite-sugilite, pale-yellow to orange aggregates and tabular crystals of reedmergnerite, black crystals of aegirine, orange-brown semi-transparent lenticular crystals of stillwellite-(Се), grass-green or yellowish-green semi-transparent and transparent crystals of leucosphenite, darkgreen crystals of turkestanite and aggregates of large white grains of microcline.Also present are fine-grained brown or greyishbrown aggregates of Mn-bearing pectolite, quartz, Sr-bearing fluorite and a variety of rare minerals.Kalyuzhnyite-(Ce) occurs in these pectolite-rich aggregates (Fig. 1a,b), associated with quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite.The origin of the silexite boulders with pectolite aggregates, in which kalyuzhnyite-(Ce) was found, is debatable as these rocks have not been investigated in situ.The problem of their genesis has been discussed by Pautov et al. (2022).

Physical properties
Kalyuzhnyite-(Ce) occurs as equant grains with poorly developed faces in a quartz-pectolite aggregate (Fig. 1a,b).The two grains of kalyuzhnyite-(Ce) up to 70 μm were found by scanning electron microscopy in a small hand-sample.One part of grain 1 (Fig. 1a) was used for the crystal-structure work (crystal 1) and the second part of grain 1 was used for the electron-microprobe analysis (crystal 2).The microprobe mount of crystal 2 was deposited as a holotype Kalyuzhnyite-(Ce), catalogue number 98144.The second smaller grain 2 up to 50 μm (Fig. 1b) was used for Raman spectroscopy (in a thin section).
The grains are colourless and have a vitreous lustre.Kalyuzhnyite-(Ce) has an uneven fracture and does not fluoresce under cathode waves or ultraviolet light.The cleavage is {010} perfect and no parting was observed.The hardness of kalyuzhnyite-(Ce) was not measured due to the very small size of grain 2. The mineral is brittle and D calc.= 3.120 g/cm 3 .
Individual grains show no visible twinning.Kalyuzhnyite-(Ce) is nonpleochroic.In reflected light, kalyuzhnyite-(Ce) is grey.Reflectance values were measured with a UMSP-50 Opton microspectrophotometer using the Opton SiC standard 474251 (with a spectral slot width of 10 nm) and are given in Table 1.Kalyuzhnyite-(Ce) has very weak bireflectance.

Raman spectroscopy
The Raman spectrum of kalyuzhnyite-(Ce) (Fig. 2) was obtained on a randomly oriented crystal (polished section, Fig. 1b) using Thermo DXR2xi Raman imaging confocal microscope with a green laser (532 nm) at room temperature.The output power of the laser beam was 10 mW (at 100% power), holographic 7.2 6.0 400 6.0 5.0 560 7.1 5.9 420 6.0 5.0 580 6.7 5.5 440 6.0 5 .0589 6.6 5.4 460 6.0 5.0 600 6.4 5 .3470 6.0 5.0 620 6.1 5.1 480 6.5 5.3 640 6.0 4.9 500 6.6 5 .4650 5.9 4.9 520 6.8 5.4 660 6.0 4.9 540 6.8 5.6 680 6.0 5 .0546 6.8 5.6 700 The reference wavelengths required by the Commission on Ore Mineralogy (COM) are given in bold.diffraction grating was used with 1800 lines cm -1 , spectral resolution was 2 cm -1 , the range was from 50 to 1800 cm -1 .The diameter of the focal spot on the sample was 2 μm.The back-scattered Raman signal was collected with a 100× objective; signal acquisition time for a single scan of the spectral range was 2.0 s and the signal was averaged over 20 scans.The spectrum was processed using Omnic software.Lines in the Raman spectrum of kalyuzhnyite-(Ce) can be grouped into three frequency ranges by analogy with data obtained for some multi-ring silicates of Na, Sr, Ti and REE (Sitarz et al., 1998;Frost and Xi, 2012;Tobbens et al., 2008).The 800-1100 cm -1 range bands are due to Si-O bond-stretching modes, the 500 to 800 cm -1 vibrations are due to O-Si-O bending modes.The spectral region lower than 500 cm -1 corresponds to Me-O stretching vibrations and lattice modes, while some bonds from 300 to 500 cm -1 can correspond to SiO 4 -unit vibrations.

Powder X-ray diffraction
Powder X-ray diffraction data were obtained by collapsing singlecrystal experimental data into two dimensions.Data (in Å for MoKα) are listed in Table 3. Unit-cell parameters are therefore the same as from the single-crystal data (Table 4).
X-ray single-crystal data collection and structure solution and refinement X-ray single-crystal data for kalyuzhnyite-(Ce) were collected from a twinned crystal with a Bruker APEX II ULTRA three-circle diffractometer with a rotating-anode generator (MoKα), multilayer optics and an APEX II 4K CCD detector.The intensities of reflections with -26 ≤ h ≤ 26, -15 ≤ k ≤ 15 and -20 ≤ l ≤ 20 were collected with a frame width of 0.3°and a frame time of 6 s up to 2θ ≤ 60.21°, and an empirical absorption correction (SADABS, Sheldrick, 2015) applied.There were few observed reflections at high 2θ, and refinement of the structure was done for 2θ ≤ 55°, −24 ≤ h ≤ 24, -14 ≤ k ≤ 15 and -19 ≤ l ≤ 19.The crystal-structure solution by direct methods and refinement were done with the Bruker SHELXTL Version 2014/3 software (Sheldrick, 2015) in space group P2/c.We refined the structure as two components related by the TWIN matrix ( 1 0 0, 0 1 0, 1 0 1).The crystal structure of kalyuzhnyite-(Ce) was refined to R 1 = 2.74%, the twin ratio being 0.5037(9) : 0.4963(9) (Table 4).Details of data collection and structure refinement are given in Table 4.The occupancies of ten cation sites were refined with the following scattering curves: M1 site: Ti; M2 site: Nd; M3 site: Sr; M4 site: Na; M(5,6) sites: Pb; M(7,8) sites: Ca; A(1,2) and B(1,2) sites: K and Cs, respectively.The occupancies of the F and X sites were refined with the  scattering curve of F, and W(1-9) sites, with the scattering curve of O. Refinement of the F, X and W1 site-occupancies converged to integer values (within 3 e.s.d.) and were subsequently fixed at full occupancy.Scattering curves for neutral atoms were taken from the International Tables for Crystallography (Wilson, 1992).Final atom coordinates and anisotropic displacement parameters are given in Table 5, selected interatomic distances and angles in Table 6, refined site-scattering values and assigned site-populations in Table 7, and bond-valence values in Tables 8 and 9.A list of observed and calculated structure factors and a Crystallographic Information File (CIF) have been deposited with the Principal Editor of Mineralogical Magazine and are available as Supplementary Material (see below).The structure diagrams were drawn using ATOMS 64 software (Dowty, 2016).
The four M sites in the heteropolyhedral sheet (Table 5) are considered next.At the [6]-coordinated M1 site, the refined scattering is 21.97 electrons per formula unit (epfu) and the mean
Consider the interstitial M(5-8), A(1,2) and B(1,2) sites.The refined site-scattering value at the M5 site is slightly higher than at the M6 site: 15.3 versus 14.7 epfu; the mean bond-length values: 2.515 and 2.531 Å, are very similar.Therefore, we allocate more Pb (the heaviest scatter) to the M5 site: Pb 0.16 Ca 0.11 □ 0.23 pfu, and less Pb to the M6 site: Sr 0.14 Ln 0.08 Pb 0.06 Ca 0.11 □ 0.22 pfu (Table 7).Based on the refined site-scattering values and observed bond-distances, we assign Na 0.25 □ 0.75 and Ca 0.14 □ 0.86 pfu to the M7 and M8 sites, respectively (Table 7).

Cation sites
The crystal structure of kalyuzhnyite-(Ce) contains three groups of cation sites: M sites of the heteropolyhedral sheet, Si sites of the Si-O sheet and interstitial M(5-8), A(1,2) and B(1,2) sites.

Heteropolyhedral sheet
There are four cation sites in the heteropolyhedral sheet: the Ti-dominant M1 site, the Ce-dominant M2 site, the Sr-dominant M3 site, and the Na-dominant M4 site (Fig. 3a).The M1 site is occupied by Ti 0.97 Nb 0.03 apfu, ideally Ti apfu.The M1 atom is octahedrally coordinated by six anions: five O atoms and one F atom, <M1-w> = 2.983 Å (w = O and F)     9), hence X is a F atom.SRO-2 (20%) occurs where the X anion does not receive bond-valence contributions from two M4 [Na] atoms [note that the M4 site is vacant at 20%, Tables 5, 7] and M(6) [Sr], but receives bond-valence contributions from two M2 [Ce] atoms and interstitial cations: M5 [Pb] and B1 [K], with a total sum of 0.61 vu (Table 9), hence X is an H 2 O group.We write the composition of the X ligand as F 0.40 (H 2 O) 0.10 pfu, ideally F 0.5 apfu (Table 7).Hence ideal composition of the anions/H 2 O groups of the heteropolyhedral sheet not shared with the Si-O sheet is O22 O 2-+ F F 0.5 0.5-+ X F 0.5 0.5-= (OF) 3-pfu.

Interstitial complex
The O atoms of H 2 O groups at the W(1-9) sites occur within the Si-O sheet in the large channels at y ≈ 0 (Fig. 4a,b;

General topology of the crystal structure
There are two main structural units in the crystal structure of kalyuzhnyite-(Ce): a heteropolyhedral sheet and a double Si-O sheet (Fig. 3a,b).The heteropolyhedral sheet parallel to (010) is composed of Ti-dominant M1 octahedra, Ce-dominant M2 polyhedra, and Sr-dominant M3 polyhedra and Na-dominant M4 polyhedra which share edges and vertices (Fig. 3a, Tables 5-7).We sum the cation and anion parts of the heteropolyhedral sheet to derive its ideal composition: (NaSrCeTi) 10+ + (OF) 3-= [NaSrCeTi(OF] 7+ .The double Si-O sheet parallel to (010) is composed of ten-membered rings of SiO 4 tetrahedra (Figs 3b,4b).The ten-membered rings occur at y ≈ + 0.265 and y ≈ -0.265 and connect via two SiO 4 tetrahedra which form an Si4-O15-Si5 bridge oriented along b (Fig. 4a; Table 6).The composition of this double Si-O sheet is (Si 8 O 21 ) 10-.Such a double Si-O sheet is newa sheet with this topology and composition has never been described in minerals before (Hawthorne et al., 2019); we call this the kalyuzhnyite sheet.The heteropolyhedral and Si-O sheets alternate along b; there is one heteropolyhedral sheet and one Si-O sheet per b unit-cell parameter (Fig. 4a).The sheets connect via common vertices of M(1-4) polyhedra and SiO 4 tetrahedra to form a framework.Summation of the ideal compositions of the heteropolyhedral sheet and double Si-O sheet, gives ideal composition of the framework: [NaSrCeTiOF] 7+ + (Si 8 O 21 ) 10-= NaSrCeTi(Si 8 O 21 )OF] 3-.The interstitial complex is composed of M(5-8), A(1,2) and B(1,2) cations and H 2 O groups at the W(1-9) sites.The interstitial complex is located within the double Si 5).The larger cations, Pb and Sr at the M(5,6) sites, Cs at the A(1,2) sites and K at the B(1,2) sites occupy centres of ten membered rings of SiO 4 tetrahedra (Fig. 4b).Smaller cations, Na and Ca at the M7 and M8 sites and H 2 O groups at the W(1-9) sites occur in the large channels along c (Figs 4a, 5b).The ideal composition is derived by a sum of cation and anion/H 2 O parts of the interstitial complex to give: (KCa) 3+ + (H 2 O) 3 = [(KCa) (H 2 O) 3 ] 3+ .

Figure 4 .
Figure 4. General view of the crystal structure of kalyuzhnyite-(Ce): (a) linkage of two double Si-O sheets and a heteropolyhedral sheet with interstitial cations at partly occupied M(5-8), A(1,2) and B(1,2) sites and H 2 O groups; (b) positions of interstitial cations and H 2 O groups within the ten-membered rings of SiO 4 tetrahedra of the double Si-O sheet.Legend as in Fig. 3, dominant cations at partly occupied sites are shown as spheres: Pb (bright yellow) at the M5 site; Sr (pink) at the M6 site; Na (blue) at the M7 site; Ca (bright pink) at the M8 site; Cs (pale orange) at the A(1,2) sites and K (green) at the B(1,2) sites; an H 2 O group at the W1 site is shown as a central O atom (red sphere) with two H atoms (small grey spheres), and O-H bonds are shown as black lines.
*Powder data were obtained by collapsing single-crystal X-ray diffraction data into two dimensions.Intensities are listed for reflections with I est.≥ 10.
*U iso

Table 9 .
Bond-valence values* (vu)for the X anion involved in short-range order in kalyuzhnyite-(Ce).