New insight into the pectolite – serandite series: a single crystal diffraction study of Na(Ca1.73Mn0.27)[HSi3O9] at 293 and 100 K (original) (raw)

A vibrational spectroscopic study of the silicate mineral pectolite – NaCa2Si3O8(OH)

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015

We have studied the hydrated hydroxyl silicate mineral inesite. Of formula Ca 2 (Mn,Fe) 7 Si 10 O 28 (OH)Á5H 2 O. Using a combination of scanning electron microscopy with EDX and Raman and infrared spectroscopy. OH stretching vibrations are readily studied. The application of vibrational spectroscopy has enabled an assessment of the molecular structure of inesite.

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.

57Fe M�ssbauer study of the asbestiform silicates balangeroite and carlosturanite

Physics and Chemistry of Minerals, 1994

57Fe M6ssbauer spectra of the two silicate minerals balangeroite (BAL) and carlosturanite (CST) have been collected at 80 and 295 K under normal and magic angle geometry. For both minerals the spectra have been fitted with two ferrous and two ferric doublets; Fe 2+ accounts for 80 and 62% of Fetot in Bal and CST, respectively. The number of doublets used to fit the spectra supports the hypotheses that: (i) in the serpentine-like structure of CST iron occupies only octahedra which lie between the tetrahedral silicate strips; (ii) the octahedral framework of BAL (actually monoclinic) is satisfactorily described with an orthorhombic sub-cell. rahedra occupy [001] channels (Ferraris et al. 1987). In the monoclinic cell with a = 19.163 (2), b = 19.224 (2), c = 9.599(3) ]k, 7 = 89-50(1) ~ (c unique axis; space group P2/ n), obtained from powder neutron-diffraction data (Belluso and Ferraris 1991), there are four formula units with composition MzlO3(OH)2o(Si~O12)2; M (octahedral cations) ~ 2 + 3 +

57Fe Moessbauer study of the asbestiform silicates balangeroite and carlosturanite

Physics and Chemistry of Minerals, 1994

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 .

New insight into the pectolite – serandite series: a single crystal diffraction study of Na(Ca1.73Mn0.27)[HSi3O9] at 293 and 100 K (original) (raw)

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