The Crystal Structure of Calcium Catapleiite

Mineralogical Magazine, 1988

The Canadian Mineralogist, 2006

The crystal structure of senkevichite, ideally Cs K Na Ca 2 Ti 4+ O [Si 7 O 18 (OH)], triclinic, P1, a 10.4191(4), b 12.2408(5), c 7.0569(3) Å, ␣ 90.857(1), ␤ 99.193(1), ␥ 91.895(1)°, V 887.8(1) Å 3 , Z = 2, D calc 3.125 g/cm 3 , from Dara-i-Pioz, Tien-Shan Mountains, Tajikistan, has been refi ned to R 1 = 4.5% for 4872 unique (F o > 4F) refl ections collected on a Bruker single-crystal P4 diffractometer equipped with a 4K CCD detector and MoK␣ X-radiation. Electron-microprobe analysis gave SiO 2 51.08, TiO 2 8.94, FeO 0.50, MnO 2.59, CaO 10.98, K 2 O 6.13, Na 2 O 3.76, Nb 2 O 5 0.64, Cs 2 O 15.28, (H 2 O) calc 1.09, sum 100.99 wt.%, and (H 2 O) was determined from crystal-structure analysis. Senkevichite is isostructural with tinaksite and tokkoite. There are seven tetrahedrally coordinated Si sites with a grand <Si-O> distance of 1.623 Å. Six of these sites are coordinated by O atoms, and the Si site is coordinated by three O atoms and one (OH) group, i.e., this is an acid silicate group. There are three [6]coordinated M sites. The M(1) site is occupied primarily by Ti 4+ (with minor Nb), with <M(1)-O> = 1.985 Å. The M(2) site is occupied solely by Ca, with <M(2)-O> = 2.382 Å, and the M(3) site is occupied by Ca (with minor Fe 2+ and Mn 2+ ), with <M(3)-O> = 2.317 Å. There is one [7]-coordinated Na site with <Na-O> = 2.504 Å. There are two A sites, the [12]-coordinated A(1) site, occupied mainly by Cs (with minor K), with <A(1)-O> = 3.318 Å, and the [10]-coordinated A(2) site, occupied solely by K, with <A(2)-O> = 2.987Å. Senkevichite is a Cs-analogue of tinaksite, K 2 Na Ca 2 Ti 4+ O [Si 7 O 18 (OH)], and a Cs-Na-Ti 4+ oxyanalogue of tokkoite, K 2 Ca 4 F [Si 7 O 18 (OH)].

Canadian Mineralogist, 2010

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American Mineralogist, 2007

Vishnevite, [Na 6 (SO 4 )][Na 2 (H 2 O) 2 ](Si 6 Al 6 O 24 ), is a relatively rare member of the cancrinite group, Þ rst found at Vishnevye Gory, Urals, Russia and later in a few other occurrences (see for a compilation). Cancrinite minerals are feldspathoids characterized by hexagonal rings of (Si, Al) tetrahedral layers stacked along [001] so as to form a three dimensional framework. Different stacking sequences are possible, and these give rise to a large variety of species. An updated list can be found in . The simple ABAB... sequence (where A and B are the position of the Þ rst and second layer in the sequence, following the nomenclature of the closest-packed structures) is common to several natural (nine up to present) and synthetic phases in this group. These AB phases can be further classiÞ ed into two series: the cancrinite-vishnevite series and the davyne-microsommite-quadridavyne series (cf. . Their framework is characterized by open 12-ring channels running along [001], and by columns of base-sharing undecahedral cages ([6 6 12 2/2 ] and [4 6 6 5 ] in the IUPAC nomenclature, respectively). In cancrinite-type minerals, the undecahedral cages contain sequences of alternating Na cations and water molecules, while the large channels are Þ lled by carbonate groups in ideal cancrinite and by sulfate groups in ideal vishnevite (e.g., Bonaccorsi and Merlino 2005). There is a complete solid solution between cancrinite and vishnevite, with intermediate terms named sulfatic cancrinite or carbonatic vishnevite (Hassan and Grundy 1984). The substitution of SO 4 2for CO 3 2groups along the cancrinite-vishnevite series is correlated with the entry of signiÞ cant amounts of K in the channels; when the (Na,Ca): K is nearly = 1, there is the possibility of long-range ordering of sulfate groups and extra-framework cations, such as in pitiglianoite, which is characterized by a threefold supercell with respect to cancrinite .

Neues Jahrbuch für Mineralogie - Monatshefte, 2002

Inorganic Chemistry, 2011

Fluor-chlorellestadite solid solutions Ca 10 (SiO 4) 3 (SO 4) 3 Cl 2−x F x , serving as prototype crystalline matrices for the fixation of hazardous fly ash, were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The lattice parameters of the ellestadites vary linearly with composition and show the expected shrinkage of unit cell volume as fluorine (IR = 1.33 Å) displaces chlorine (IR = 1.81 Å). FTIR spectra indicate little or no OH − in the solid solutions. All compositions conform to P6 3 / m symmetry where F − is located at the 2a (0, 0, 1 / 4) position, while Cl − is displaced out of the 6h Ca(2) triangle plane and occupies 4e (0, 0, z) split positions with z ranging from 0.336(3) to 0.4315(3). Si/S randomly occupy the 6h tetrahedral site. Ellestadites rich in Cl (x ≤ 1.2) show an overall deficiency in halogens (<2 atom per formula unit), particularly Cl as a result of CaCl 2 volatilization, with charge balance achieved by the creation of Ca vacancies (Ca 2+ + 2Cl − →□ Ca + 2□ Cl) leading to the formula Ca 10−y (SiO 4) 3 (SO 4) 3 Cl 2−x−2y F x. For F-rich compositions the vacancies are found at Ca(2), while for Cl-rich ellestadites, vacancies are at Ca(1). It is likely the loss of CaCl 2 which leads tunnel anion vacancies promotes intertunnel positional disorder, preventing the formation of a P2 1 /b monoclinic dimorph, analogous to that reported for Ca 10 (PO 4) 6 Cl 2. Trends in structure with composition were analyzed using crystal-chemical parameters, whose systematic variations served to validate the quality of the Rietveld refinements. 65 rellestadites are regarded as isostructural, although the halides 66 reside at different locations along the c-axis anion tunnels. In 67 the synthetic fluorellestadite (P6 3 /m) endmember, F − at (0, 0, 68 1/4 and 0, 0, 3 / 4) lies in the center of a Ca(2) triangle on the 69 mirror planes at z = 1/4 and z = 3 / 4. 12 In the corresponding 70 chlorellestadite endmember, Cl − cannot fit into the Ca(2) 71 triangle (ionic radii for VI F − = 1.33 Å and VI Cl − = 1.81 Å 13), 72 and statistically occupies (0, 0, z) sites, ∼1.1 Å above or below 73 the mirror plane. 9 In the case of natural hydroxyellestadite, 74 Sudarsanan 7 refined separate sites for OH − (0, 0, 0.2033), F − 75 (0, 0, 1 / 4), and Cl − (0, 0, 0.3644) in P2 1 /m with site 76 occupancies of 0.806(9), 0.15(6), and 0.092(5) respectively.

A b s t r a c t. Dovyrenite, simplified formula Ca 6 Zr[Si 2 O 7 ] 2 (OH) 4 , occurs as an accessory mineral in vein skarns developed in carbonate xenoliths in subvolcanic layered plagiodunite-troctolite series in the Ioko-Dovyren Massif of Proterozoic age, Northern Baikal Region, Buryatia, Russia. Dovyrenite is a late mineral of altered pyroxene and melilite-monticellite skarns. Associated minerals are Zr-bearing phases: fassaitic pyroxene, perovskite and hydrogarnets; and also monticellite, The average structure of dovyrenite is orthorhombic, space group Pnnm, with subcell parameters A = 5.666(16) C, B = 18.844(5) C, C = 3.728(11) C, V = 398.0(2) C 3 and Z = 1. Dovyrenite shows a new type of modular structure with stacking of the tobermorite-like and the rosenbuschite-like layers parallel to (010). Single-crystal structural data point to an incompletely occupied Ca(2) site from the rosenbuschite module which is confirmed by microprobe analyses: ZrO 2 16.47, SiO 2 32.83, TiO 2 0.14, HfO 2 0.16, Cr 2 O 3 0.01, CaO 43.87, FeO 0.25, MgO 0.13, MnO 0.02, Nb 2 O 3 0.03; total 99.38 wt% with calculated H 2 O. The empirical formula is (Ca 5.73 Fe 0.03 Mg 0.02) S5.78 (Zr 0.98 Hf 0.01 Ti 0.01) S1 Si 4 (O 13.56 OH 0.44) S14 (OH) 4. The presence of two types of OH group in the dovyrenite structure is corroborated by FTIR and Raman spectroscopy. Dovyrenite is an optically positive biaxial mineral: a 1.659(2), b 1.660(2); g 1.676(2); 2Vz 30(5)° (measured), 28° (calculated). The coexistence of monticellite, foshagite and dovyrenite points to a narrow interval of crystallization 560–630°C under subvolcanic conditions (P < 10 8 Pa).

American Mineralogist, 1981

X-ray diffraction intensities were measured by single-crystal diffractometry (MoKa radiation) on picropharmacolite from Sainte-Marie-aux-Mines (Alsace), and the following structuro parameters were determined: a: 13.547(3), D : 13.500(3), c : 6.710(l)A, a : 99.85(l), f :96.41(2), y : 91.60(l)"; Z :2, space group PT. The structure was solved by direct methods; the mixed isotropic (oxygen atoms) and anisotropic (heavier atoms) refinement converged to R : 0.087 (16l I reflections). As, Ca, and Mg coordination polyhedra sharing edges and vertices form corrugated (100) layers, which are linked by hydrogen bonding only. Four independent water molecules are sandwiched between adjacent layers, and build up [001] hydrogen-bonded chains. The Mg coordination octahedron and the Ca polyhedra show typical bond distances, so that no signifcant Ca/Mg substitution should occur in any cation site. The formula of picropharmacolite can then be written as CaoMg(HrO).,(AsO3OH)2(AsOa)2' 4HrO. A close relationship is observed between this structure and those of the two dimorphs guerinite and ferrarisite, Car(HAsOo)r(AsOo)2.9HrO; in these minerals the layers of polyhedra are also present, but are linked by Ca-O bonds in addition to hydrogen bonds. Cleavage and possible [winning are discussed on structural grounds.

The Canadian Mineralogist, 2000

The crystal structure of a new mineral species, bakhchisaraitsevite [Na 2 (H 2 O) 2 ]{(Mg,Fe) 5 (H 2 O) 5 (PO 4) 4 }, a 8.3086(8), b 12.906(1), c 17.486(2) Å, ␤ 102.01(1)°, V 1834.0(1) Å 3 , space group P2 1 /c, Z = 4, calc = 2.499 g/cm 3 , has been determined [automated single-crystal diffractometer, MoK␣, graphite monochromator, T = 193 K, 21597 reflections, R = 0.033 for 3527 unique reflections with I ≥ 2(I), wR 2 = 0.072]. It can be described as an open framework of Mg(Fe) octahedra and PO 4 tetrahedra. Extremely contorted chains of edge-sharing Mg(Fe) octahedra form layers parallel to the ab plane. The unit cell of bakhchisaraitsevite contains two layers of this kind. In the c direction, these layers are also joined by dimers of Mg(Fe) octahedra having common edges. The PO 4 tetrahedra consolidate the structure, sharing the majority of vertices with octahedra. Na atoms and H 2 O molecules are distributed in the channels of an open framework. The main feature of the crystal structure, layers of octahedra parallel to the ab plane, explains the flattened habit and the perfect cleavage of the crystals. The crystal-chemical formula of the mineral, [Na 2 (H 2 O) 2 ]{(Mg 4.5 Fe 0.5)(H 2 O) 5 (PO 4) 4 }, where curly brackets enclose the framework component and square brackets show the contents of the channels, reflects the different functions of the H 2 O molecules in the structure. Bakhchisaraitsevite as a possible biomineral can be expected to play a role in accumulating phosphorus in recent sulfidic sediments with the participation of bacteria. We describe the close structural relations between bakhchisaraitsevite and rimkorolgite.