Yu. K. Egorov-Tismenko

Refined crystal structure of lovozerite Na2CaZr[Si6O12(OH,O)6] · H2O

AbstractThe structure of Na,Ca,Zr-silicate lovozerite, Na2CaZr[Si6O12(OH,O)6] · H2O, from the Khibiny alkaline massif (the Kola Peninsula) was refined by single-crystal X-ray diffraction analysis (Syntex

Crystal structure of new synthetic calcium pentaborate Ca[B5O8(OH)] · H2O and its relation to pentaborates with similar boron-oxygen radicals

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Crystal structure of tisinalite Na2(Mn,Ca)1 − x(Ti,Zr,Nb,Fe3+)[Si6O8(O,OH)10]

diffractometer, λMoKα radiation, 2θ/θ scanning technique). The refinement (Rhkl = 0.077, 1531 independent reflections; anisotropic thermal parameters) confirmed the trigonal system proposed for the mineral earlier (sp. gr. R3; a = 10.18(1) Å, c = 13.13(2) Å, Z = 3) and revealed the presence of two additional positions (C and B) statistically occupied by Ca and Na atoms (and partly by Mn) and H2O molecules, respectively.

Refined crystal structure of iron-rich triclinic astrophyllite

A calcium analog of strontioborite, namely, Ca[B8O11(OH)4], is synthesized under hydrothermal conditions (T = 270°C, P = 20 atm) within the framework of the study of the phase formation in the CaCl2 · Rb2CO3 · B2O3 system. The crystal structure of the synthetic calcium borate [a = 7.4480(5) Å, b = 8.2627(5) Å, c = 9.8102(6) Å, β = 108.331(1)°, V = 573.09(6) Å3, space group P21, Z = 2, ρcalcd = 2.15 g/cm3; Brucker SMART CCD automated diffractometer, 5506 reflections, λMoKα] is refined by the least-squares procedure in the anisotropic approximation of thermal atomic vibrations to R1 = 0.050. The calcium borate studied has a crystal structure identical to the structure of the natural strontium borate (strontioborite) Sr[B8O11(OH)4] and its calcium analog synthesized earlier. The crystal structure is built up of stacks consisting of skeleton layers (formed by boron-oxygen polyanions) and isolated strontium (calcium) polyhedra located in trigonal holes of the skeleton layers. Through channels that can contain H2O molecules are formed between the stacks. The structure refinement and analysis of the IR spectrum of the synthetic calcium analog of strontioborite do not confirm the previously proposed hypothesis that water molecules are involved in the channels of the structure. A comparative crystal chemical analysis of the calcium borate under investigation and its formula analog, namely, the lead borate Pb[B8O11(OH)4], is performed.

Crystal structure of new synthetic Ca,Na,Li-carbonate-borate

A new representative of pentaborates with the composition Ca[B5O8(OH)] · H2O was synthesized under hydrothermal conditions within the framework of the study of phase formation in the CaCl2-Na2CO3-B2O3 system. The crystal structure of the new pentaborate was established (a = 6.5303(9) Å, b = 19.613(3) Å, c = 6.5303(9) Å, β = 119.207(2)°, V = 2513(2) Å3, sp. gr. P21/c, Z = 4, dcalcd = 2.74 g/cm3, automated Brucker SMART CCD diffractometer, 6871 reflections, λMo radiation, anisotropic refinement by least-squares, Rhkl = 0.076). The structure of calcium pentaborate is built by isolated B-Ca-B stacks parallel to the (010) plane. The central fragments of these stacks consists of nine-vertex Ca polyhedra. The Ca layers are located between loose B-O networks composed of [B2t B3Δ O8(OH)]2− pentaborate groups. The arrangement of the polyhedra around large cations in pentaborates with groups of two B tetrahedra and three B triangles was analyzed in terms of crystal chemistry. It is established that the structures of these compounds consist of large isolated polyhedra, columns, layers, and three-dimensional frameworks.

Crystal structure of a new synthetic Ca,Li pentaborate: CaLi4[B5O8(OH)2]2

AbstractA new representative of the lovozerite group—Na, Zr, Mn-silicate litvinskite (Na, H2O, □) 3(□, Na, Mn2+)Zr[Si6O12(OH)3(OH, O)3]—was discovered in ultraagpaitic pegmatites from the Lovozero massif. The crystal structure of the mineral was solved on an automated Syntex P

Crystal structure of jaffeite

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