Vladimir Y. Karpenko

Yusupovite, Na2Zr(Si6O15)(H2O)3, a new mineral species from the Darai-Pioz alkaline massif and its implications as a new microporous filter for large ions

Abstract Yusupovite, ideally Na2Zr(Si6O15)(H2O)3, is a new silicate mineral from the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, area of the joint Turkestansky, Zeravshansky, and Alaisky ridges, Tajikistan. Yusupovite was found in a pegmatite composed mainly of reedmergnerite, aegirine, microcline, and polylithionite. It occurs as prismatic grains about 2 mm in size embedded in reedmergnerite; associated minerals are quartz, pectolite, zeravshanite, mendeleevite-(Ce), fluorite, leucosphenite, a pyrochlore-group mineral, neptunite, telyushenkoite, moskvinite-(Y), and shibkovite. Yusupovite is colorless, transparent with a white streak, has a vitreous luster, and does not fluoresce under ultraviolet light. Cleavage is perfect on {110}, parting was not observed. Mohs hardness is 5. Yusupovite is brittle with a splintery fracture. The measured and calculated densities are 2.69(2) and 2.713 g/cm3, respectively. Yusupovite is optically biaxial (+) with refractive indices (λ = 589 nm) α = 1.563(2), β = 1.565(2), γ = 1.577(2); 2Vmeas = 42(3)°, 2Vcalc = 45°, strong dispersion: r > v. Yusupovite is monoclinic, C2/m, a = 14.5975(4), b = 14.1100(4), c = 14.4394(4) Å, β = 90.0399(4)°, V = 2974.1(3) Å3. The six strongest reflections in the X‑ray powder diffraction data [d (Å), I, (hkl)] are 7.05, 100, (020); 3.24, 96, (420); 3.10, 69, (241, 2̅41); 5.13, 53, (202, 2̅02); 6.51, 42, (201, 2̅01); 3.17, 34, (042). The chemical composition (electron microprobe) is: Nb2O5 0.39, SiO2 58.84, ZrO2 16.55, HfO2 0.30, FeO 0.01, Y2O3 3.05, Cs2O 2.58, K2O 0.95, Na2O 8.91, H2Ocalc 7.40, total 98.98 wt%, with H2O calculated from structure refinement. The empirical formula (based on 17.5 O apfu) is (Na1.76K0.12Cs0.11)∑1.99 (Zr0.82Y0.17Nb0.02Hf0.01)∑1.02(Si6.01O14.98)(H2O)2.52, Z = 8. The crystal structure of yusupovite was refined to R1 = 3.46% based on 4428 observed reflections. In the crystal structure, there are six Si sites occupied by Si, two M sites occupied mainly by Zr with minor Y and Hf. Si tetrahedra form an epididymite Si6O15 ribbon along [010]. Epididymite ribbons and Zr-dominant M octahedra share common vertices to form a heteropolyhedral Si-Zr-O framework. There are six interstitial sites partly occupied by alkali cations Na, K, and Cs. The three [7]-coordinated Na sites are occupied by Na at 95, 84, and 78%. The three A sites are occupied by K and Cs at 12, 18, and 16%. There are 10 W sites occupied by H2O groups at 18-84%. Due to (K,Cs), Na and H2O disorder, the symmetry of yusupovite decreases from orthorhombic, space group Pbcm (elpidite), to monoclinic, space group C2/m, and the b unit-cell parameter of yusupovite is doubled compared to the corresponding cell parameter in elpidite, byus = 2aelp. Yusupovite, ideally Na2Zr(Si6O15)(H2O)3, is a dimorph of elpidite, Na2Zr(Si6O15)(H2O)3.

The crystal structure of laptevite-(Ce), NaFe2+(REE7Ca5Y3)(SiO4)4(Si3B2PO18)(BO3)F11, a new mineral species from the Darai-Pioz alkaline massif, Northern Tajikistan

Abstract Laptevite-(Ce), ideally NaFe2+(REE7Ca5Y3) · (SiO4)4(Si3B2PO18)(BO3)F11, is a new member of the vicanite group discovered in the moraine of the Darai-Pioz glacier, Alai Mountain Range, Tien-Shan, Tajikistan. The crystal structure of laptevite-(Ce), trigonal, a = 10.804(2) Å , c = 27.726(6) Å , V = 2802.6(2) Å 3, sp. gr. R3m, Z = 3, Dcalc. = 4.660 · 103 kg/m3, has been refined to R1 = 0.0387 for 924 unique (Fo > 4σF) reflections, collected on a Bruker single-crystal P4 diffractometer with a 4K CCD detector and Mo-Ka X-radiation. The simplified formula is NaFe2+(REE,Ca,Y)15(SiO4)4 [(Si,B,P)6O18](BO3)F11. In the crystal structure of laptevite-( Ce), there are four tetrahedrally coordinated T sites. The T(1) site is occupied by Si and minor B, 〈T(1)-O〉 = 1.594 Å ; the T(2, 3) sites are occupied by Si, 〈T(2,3)-O〉 = 1.64 Å ; the T(4) site is occupied by B, P and minor Si, with 〈T(4)-O〉 = 1.51 Å . The [3]-coordinated T(5) site has composition B0.84⃞0.16, with 〈T(5)-O〉 = 1.42 Å . Cations at the T(1 + 4), T(2, 3) and T(5) sites form the complex anions (Si3B2PO18), (SiO4)4 and (BO3), respectively. The [7-10-coordinated M(1-5) sites are occupied by REE, Ca, Y and minor Sr, with 〈M(1-5)-O〉 = 2.37-2.62 Å . The octahedrally coordinated M(6) site is occupied by Fe2+ > Mn > Ti, with 〈M(6)-O〉 =2.13 Å . The [10]-coordinated M(7) site has composition Na0.75REE0.25, with 〈M(7)-O〉 = 2.64 Å . The T and M polyhedra form a framework. Laptevite-(Ce) is isostructural with other vicanite-group minerals: vicanite- (Ce), okanoganite-(Y), hundholmenite-(Y) and proshchenkoite-(Y). Vicanite-group structures differ in the dominant cation species at the T(1, 3-6) and M(3-7) sites.

Mendeleevite-(Nd), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH,H2O,F)35, a new mineral from the Darai-Pioz alkaline massif, Tajikistan

Abstract Mendeleevite-(Nd), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH,H2O,F)35 is a new mineral from the Darai-Pioz alkaline massif, Tajikistan. Mendeleevite-(Nd) was found in a pectolite aggregate in silexites (quartz-rich rocks) which consist of fine to medium pectolite grains, quartz, aegirine and fluorite, with minor khvorovite, mendeleevite-(Ce), sokolovaite, hyalotekite, orlovite, kirchhoffite, pekovite, neptunite, zeravshanite, senkevichite, nordite-(Се), alamosite, pyrochlore-group minerals and baratovite. Mendeleevite-(Nd) forms colourless cubic crystals 10-40 μm in size; it has a vitreous lustre and a Mohs hardness of 5-5.5; Dmeas. = 3.20(2) g/cm3, Dcalc. = 3.155 g/cm3. Mendeleevite-(Nd) is optically isotropic, with the refractive index n = 1.582(2). Mendeleevite-(Nd) is cubic, space group Pm3̅, a = 21.9106(4) Å; Z = 2. The six strongest reflections in the powder X-ray diffraction pattern are [d (Å), I (%), (h k l)] are: 11.01, 100, (0 0 2); 15.63, 55, (0 1 1); 3.47, 42, (2 0 6); 3.099, 42, (3 4 5); 2.192, 42, (0 0 10); 1.819, 41, (3 6 10). Chemical analysis by electron microprobe gave SiO2 42.30, Ce2O3 10.12, La2O3 3.60, Nd2O3 16.19, Pr2O3 2.79, Sm2O3 4.19, Gd2O3 1.69, Eu2O3 0.47, SrO 2.99, CaO 2.20, Cs2O 8.50, K2O 0.85, H2O 3.85, F 1.25, -O = F2 -0.53, sum 100.46 wt.%, with H2O calculated by analogy with mendeleevite-(Ce). The empirical formula based on 210 (O + F) apfu, with F + OH + H2O = 35 pfu, is Cs6(□4.20K1.80)Σ6{[(Nd9.57Ce6.13Sm2.39La2.20Pr1.68Gd0.93Eu0.27)Σ23.17(Ca3.90Sr2.87)Σ6.77]Σ29.94□0.06}Σ30(Si70.03O175)(OH14.47F6.54)Σ21.01(H2O)14, Z = 2. The simplified and ideal formulae are (Cs,□)6(□,Cs)6(□,K)6(REE,Ca)30(Si70O175)(OH, H2O,F)35 and Cs6(REE23Ca7)(Si70O175)(OH,F)19(H2O)16, respectively. The compatibility index (from measured density) = -0.039 (excellent). Mendeleevite-(Nd) is a Nd analogue of mendeleevite-(Ce), (Cs,□)6(□,Cs)6(□,K)6(REE,Ca,□)30(Si70O175)(H2O,OH,F,□)35. Both minerals are named after Dmitri Mendeleev (1834-1907), the great Russian chemist, author of the periodic table of chemical elements, who has had a significant impact on the development of natural sciences and industry, both in Russia and around the world.

Odigitriaite, CsNa5Ca5[Si14B2O38]F2, a new caesium borosilicate mineral from the Darai-Pioz alkaline massif, Tajikistan: Description and crystal structure

Abstract Odigitriaite, a new Cs,Na,Ca borosilicate mineral, was discovered in moraine adjacent to the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river at the intersection of the Turkestansky, Zeravshansky and Alaisky mountain ridges, Tajikistan. It occurs as irregular thin flakes associated with quartz, pectolite, baratovite, fluorite, pekovite, polylithionite, aegirine, leucosphenite, pyrochlore, neptunite, reedmergnerite, mendeleevite-(Се), zeravshanite and sokolovaite. It is colourless with a white streak, is translucent and has a vitreous lustre; it does not fluoresce under ultraviolet light. Odigitriaite is brittle with an uneven fracture and a Mohs hardness of 5. The calculated density is 2.80(2) g/cm3. The indices of refraction are α = 1.502, β = 1.564, γ = 1.576; 2Vobs = 46(2)°, dispersion is weak r > v, and there is no pleochroism. The chemical composition is as follows (electron microprobe, H2O calculated from structure): SiO2 55.30, Al2O3 0.09, Y2O3 0.44, MnO 0.94, FeO 0.10, PbO 0.21, K2O 0.01 Cs2O 8.36, B2O3 4.75, H2O 0.37, F 1.74, O = F2 -0.74, total 99.43 wt.%. The empirical formula of odigitriaite is Cs0.90Na5.12Ca4.68Mn0.20Y0.06Fe0.02Pb0.01[Si13.92Al0.03B2.06O38]F1.39(OH)0.62. The end-member formula is CsNa5Ca5[Si14B2O38]F-. The strong reflections in the powder X-ray diffraction pattern are: [(d, Å), (I, %), (hkl)]: 5.45 (25) (1 1 3), 4.66 (33) (3 1 1), 4.40 (26) (0 2 2), 4.10 (36) (3̅ 1 3), 3.95 (25) (3 1 3), 2.85 (31) (2 2 2), 2.68 (40) (0 0 6), 3.62 (45) (0 2 4), 3.35 (100) (2̅ 2 4), 3.31 (30) (3̅ 1 5), 3.25 (35) (4 0 4), 3.04 (60) (4̅ 2 2), 2.925 (22) (4̅ 2 3), 1.813 (23) (9 1 0). Odigitriaite is monoclinic, space group C2/c, a = 16.652(5), b = 9.598 (3), c = 22.120(7) Å, β = 92.875(14)°, V = 3530.9(1.9) Å3, Z = 4. The crystal structure of odigitriaite was solved by direct methods and refined to an R1 value of 2.75% based on single-crystal X-ray data. It is a double-layer sheet-borosilicate mineral; Cs and Na are intercalated within the double-layer sheet, and the double layers are linked by interstitial Ca and Na atoms.

Khvorovite, Ca2[Si8B2(SiB)O28]F, a new hyalotekite-group mineral from the Darai-Pioz alkaline massif, Tajikistan: Description and crystal structure

Abstract Khvorovite, ideally Pb2+4 Ca2[Si8B2(SiB)O28]F, is a new borosilicate mineral of the hyalotekite group from the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, Tajikistan. Khvorovite was found in a pectolite aggregate in silexites (quartz-rich rocks). The pectolite aggregate consists mainly of pectolite, quartz and fluorite, with minor aegirine, polylithionite, turkestanite and baratovite; accessory minerals are calcite, pyrochlore-group minerals, reedmergnerite, stillwellite-(Ce), pekovite, zeravshanite, senkevichite, sokolovaite, mendeleevite-(Ce), alamosite, orlovite, leucosphenite and several unknown Cs-silicates. Khvorovite occurs as irregular grains, rarely with square or rectangular sections up to 150 mm, and grain aggregates up to 0.5 mm. Khvorovite is colourless, rarely white, transparent with a white streak, has a vitreous lustre and does not fluoresce under ultraviolet light. Cleavage and parting were not observed. Mohs hardness is 5-5.5, and khvorovite is brittle with an uneven fracture. The measured and calculated densities are 3.96(2) and 3.968 g/cm3, respectively. Khvorovite is biaxial (+) with refractive indices (λ = 589 nm) α = 1.659(3), βcalc. = 1.671(2), γ = 1.676(3); 2Vmeas. = 64(3)°, medium dispersion: r < v. Khvorovite is triclinic, space group I1̄ , a = 11.354(2), b = 10.960(2), c = 10.271(2) Å, α = 90.32(3), β = 90.00(3), γ = 90.00(3)°, V = 1278(1) Å3, Z = 2. The six strongest lines in the powder X-ray diffraction pattern [d (Å), I, (hkl)] are: 7.86, 100, (110); 7.65, 90, (1.01); 7.55, 90, (011); 3.81, 90, (202); 3.55, 90, (301); 2.934, 90, (3. 12, 312). Chemical analysis by electron microprobe gave SiO2 36.98, B2O3 6.01, Y2O3 0.26, PbO 40.08, BaO 6.18, SrO 0.43, CaO 6.77, K2O 1.72, Na2O 0.41, F 0.88, O=F -0.37, sum 99.35 wt.%. The empirical formula based on 29 (O+F) a.p.f.u. is (Pb2+2.76Ba0.62K0.56Na0.16)Σ4.10(Ca1.86Sr0.06Y0.04Na0.04)Σ2 [Si8B2(Si1.46B0.65)Σ2.11O28](F0.71O0.29) , Z = 2, and the simplified formula is (Pb2+,Ba,K)4Ca2[Si8B2(Si,B)2O28]F. The crystal structure of khvorovite was refined to R1 = 2.89% based on 3680 observed reflections collected on a four-circle diffractometer with MoKα radiation. In the crystal structure of khvorovite, there are four [4]-coordinated Si sites occupied solely by Si with = 1.617 Å. The [4]-coordinated B site is occupied solely by B, with = 1.478 Å. The [4]-coordinated T site is occupied by Si and B (Si1.46B0.54), with = 1.605 Å; it ideally gives (SiB) a.p.f.u. The Si, B and T tetrahedra form an interrupted framework of ideal composition [Si8B2(SiB)O28]11-. The interstitial cations are Pb2+, Ba and K (minor Na) [A(11-22) sites] and Ca [M site]. The two A sites are each split into two subsites ~0.5 Å apart and occupied by Pb2+ and Ba + K. The [8]-coordinated M site is occupied mainly by Ca, with minor Sr, Y and Na. Khvorovite is a Pb2+- analogue of hyalotekite, (Ba,Pb2+,K)4(Ca,Y)2[Si8(B,Be)2(Si,B)2O28]F and a Pb2+-, Ca-analogue of kapitsaite-(Y), (Ba,K)4(Y,Ca)2[Si8B2(B,Si)2O28]F. It is named after Pavel V. Khvorov (b. 1965), a Russian mineralogist, to honour his contribution to the study of the mineralogy of the Darai-Pioz massif.