Description and crystal structure of vajdakite, [(Mo 6+ O 2 ) 2 (H 2 O) 2 As 3+ 2 O 5 ]· H 2 O—A new mineral from Jáchymov, Czech Republic (original) (raw)
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Single-crystal FTIR and X-ray study of vishnevite, ideally [Na6(SO4)]Na2(H2O)2
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 .
Journal of Raman Spectroscopy, 2010
Raman spectra of vajdakite, [(Mo 6+ O 2 ) 2 (H 2 O) 2 As 3+ 2 O 5 ]·H 2 O, were studied and interpreted in terms of the structure of the mineral. The Raman spectra were compared with the published infrared spectrum of vajdakite. The presence of dimolybdenyl and diarsenite units and of hydrogen bonded water molecules was inferred from the Raman spectra which supported the known and published crystal structure of vajdakite. Mo-O and O-H· · ·O bond lengths were calculated from the Raman spectra.
The crystal structure and hydrogen bonding of synthetic konyaite, Na2Mg(SO4)2{middle dot}5H2O
American Mineralogist, 2009
The crystal structure of synthetic konyaite, Na 2 Mg(SO 4) 2 •5H 2 O, a = 5.7690(8), b = 23.951(3), c = 8.0460(11) Å, β = 95.425(2)°, V = 1106.8(3) Å 3 , space group P2 1 /c, Z = 4, was solved using singlecrystal X-ray diffraction. Hydrogen atom positions were determined and the structure solution was refined to R 1 = 3.31% and wR 2 = 6.28% for the 2167 measured independent reflections. Three distinct cation sites host the Mg and Na atoms in distorted octahedra and eight-coordinated polyhedra. The coordination polyhedra share edges to form compact sheets oriented perpendicular to b and linked to one another by hydrogen bonds. This results in a {010} tabular habit. A comparison of this structure is made to that of blödite [Na 2 Mg(SO 4) 2 •4H 2 O], the dehydration product of konyaite. Konyaite is discussed within the context of the Na 2 O-MgO-SO 4-H 2 O system. This study is part of ongoing investigations into the dehydration mechanisms and phase stability of this system.
Hydrogen bonding in the crystalline state. Crystal structure of MgHAsO4.7H2O, roesslerite
Acta crystallographica, 1973
Calcium hydrogen arsenate trihydrate (CaHAsO4.3H20) crystallizes in the orthorhombic system, space group Pbca. Unit-cell parameters are: a0 = 11.195 (1), b0 = 10.713 (2), Co = 11" 179 (2) ~; Z = 8. The crystal structure was refined anisotropically to R=0.034, using 1321 non-zero reflexions measured on an automatic three-circle diffractometer (Cu Ke radiation). Corrections for absorption, secondary extinction and anomalous scattering were applied. The hydrogen atoms were located from a difference map, and one of the three water molecules appears very weakly hydrogen bonded. CaHAsO4.3H20 is isostructural with MgHPO4.3H20 (newberyite) and with MnHPO4.3H20; its crystal structure is built up from isolated Ca octahedra sandwiched between As tetrahedra. The resulting layers, parallel to (100), are connected by infinite zigzag chains of hydrogen bonds along [100]. Some common features of the related compounds CaHAsO4 (weilite), CaHAsO4. H20 (haidingerite), and CaHAsO4.2H20 (pharmacolite) are discussed. © Experimental Crystals of TPV suitable for X-ray diffraction measurements were kindly supplied by Dr F. A. Neuge
The composition and structure of jeanbandyite and natanite
Mineralogical Magazine, 1998
The rare iron-tin hydroxide minerals natanite and jeanbandyite occur as small pseudo-octahedral crystals in high-tcmperature Sn-Cu-As vcins at Penberthy Croft Mine and Hingston Downs Quail)', Cornwall. The lattice paramctcrs for jeanbandyite and natanite are reported and compared to previously calculated values. Thc chemical composition of jcanbandyite is discusscd and a significant proportion of divalent Fe and Mn is shown to be prcscnt.
Mineralogical Magazine
The crystal structure of kyzylkumite, ideally Ti2V3+O5(OH), from the Sludyanka complex in South Baikal, Russia was solved and refined (including the hydrogen atom position) to an agreement index, R1, of 2.34% using X-ray diffraction data collected on a twinned crystal. Kyzylkumite crystallizes in space group P21/c, with a = 8.4787(1), b = 4.5624(1), c = 10.0330(1) A˚ , b = 93.174(1)º, V = 387.51(1) A ˚ 3 and Z = 4. Tivanite, TiV3+O3OH, and kyzylkumite have modular structures based on hexagonal close packing of oxygen, which are made up of rutile [TiO2] and montroseite [V3+O(OH)] slices. In tivanite the rutile:montroseite ratio is 1:1, in kyzylkumite the ratio is 2:1. The montroseite module may be replaced by the isotypic paramontroseite V4+O2 module, which produces a phase with the formula Ti2V4+O6. In the metamorphic rocks of the Sludyanka complex, vanadium can be present as V4+ and V3+ within the same mineral (e.g. in batisivite, schreyerite and berdesinskiite). Kyzylkumite has a ...
Balestraite, KLi2VSi4O10O2, the first member of the mica group with octahedral V5+
A mica-group mineral characterized by a high V content and free of Al was found in the manganesiferous beds within the metacherts of the ophiolitic sequences at the Cerchiara mine, Eastern Liguria (Italy), in association with hematite, quartz, and calcite. Chemical and structural characterization supported by Raman data defines this phase as a new mineral species, which is named balestraite after Corrado Balestra, a prominent Italian amateur mineralogist. Balestraite, ideally KLi 2 V 5+ Si 4 O 10 O 2 , is a 1M trioctahedral mica crystallizing in the C2 space group, with a = 5.2024(5), b = 8.9782 , c = 9.997(2) Å, b = 100.40(2)°, V = 459.3(1) Å 3 , Z = 2. The reduction of symmetry from the "ideal" space group C2/m is related to the ordering of V at only one of the two pseudo-symmetric octahedral sites. Vanadium forms very distorted octahedra with a [2+2+2] geometry characteristic of the valence state +5. The Li,V composition of the octahedral sheet, the pure tetrasilicic character of the tetrahedral sheet, and the anhydrous character produce unusual geometrical features for this mica. The occurrence of 5+ as the dominant valence state of V and the virtually complete O 2-→ OHsubstitution at the O4 site indicate strongly oxidizing conditions of crystallization, which are consistent with balestraite occurring at the boundary between carbonate-bearing veins and hematite bands.
European Journal of Mineralogy, 2001
Krettnichite, PbMn 3+ 2 (VO 4 ) 2 (OH) 2 , occurs as an accessory ore mineral and as free crystals in vugs within the hydrothermal manganite-quartz vein at the historic manganese deposit of Krettnich, Saarland, Germany. Other vein minerals include barite, ankerite, calcian mottramite (minor ore constituents), barian brackebuschite, cobaltoan pyrobelonite, and calcian mottramite (free crystals in vugs). Krettnichite is monoclinic, space group C2/m, Z = 2, a = 9.275(7) Å, b = 6.284(3) Å, c = 7.682(2) Å, b = 117.97(4)°. Krettnichite is brown to black with red internal reflections. It has an excellent cleavage parallel to (001). A distinct cleavage intersecting (001) at high angle is visible in polished section. Polysynthetic twinning with composition plane (001) is common. Under plane polarised reflected light, krettnichite is slightly pleochroic, from very light grey to light brownish grey, and the anisotropy is strong under crossed polars.
The crystal structure of picropharmacolite, Ca 4 Mg(HAsO 4 ) 2 (AsO 4 ) 2 .11H 2 O
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.