1,720,964 research outputs found
Le peridotiti metamorfosate del M.te Capanne (Isola d'Elba). I. Chimismo delle fasi presenti in una peridotite di S. Piero in Campo.
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New crystal-chemical and structural data of dietrichite, ideally ZnAl<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>•22H<sub>2</sub>O, a member of the halotrichite group
No full textNew crystal-chemical and structural data of a sample of dietrichite, ideally ZnAl2(SO4)4·22H2O, from the pyrite mine of
Boccheggiano, Grosseto, Italy, are reported. This sample, unlike holotype dietrichite, is very close to the ideal chemical composition, in fact combined ICP and thermogravimetry indicate a formula (Zn0.98Fe0.07)Al1.91(SO4)4.03·21.88H2O based on 38O. The crystal structure has been refined by the Rietveld method on transmission X-ray powder diffraction data (Rp = 4.13%, Rwp = 5.44%, RB = 4.66%). Dietrichite is monoclinic P21/c, Z = 4, a = 6.1757(2), b = 24.262(1), c = 21.206(1) Å, = 100.436(3)°. The structure of
dietrichite consists of one ZnO(H2O)5 octahedron, two independent Al(H2O)6 octahedra, and four independent SO4 tetrahedra per
asymmetric unit. The only direct connection between polyhedra is by sharing of an oxygen atom, O(16), between S(4) and Zn. The
structure contains 22 water molecules, 17 of which are octahedrally co-ordinated with Zn and Al cations whereas the remaining five
molecules are only linked via hydrogen bonds to O or other H2O molecules. Hexagonal channels, running along [100], originate from
a regular alternation of one ZnO(H2O)5 octahedron, two Al(H2O)6 octahedra, and three SO4 tetrahedra. Within the structure two types
of channels may be identified, the first one containing three and the second two H2O molecules. Band positions of the IR spectrum
of dietrichite are consistent with those of reference data
Cr-rich spinel chemistry of the serpentinites from the Island of Elba, Tuscany, Italy: note I.
No full textThaumasite from the Tschwinning Mine, South Africa
No full textThaumasite from the manganese mine of Tschwinning, South Africa, has the formula Ca3.097 Si1.062OH6.372(CO3)0.994(SO4)1.000·11.596 H2O. Unit cell parameters (a=11.013(2) Å,c=10.379(5) Å,V=1090.1(6) Å3) and refraction indices (ne=1.458(2),n o=1.498(2)) compare well with the best ones available in the literature. The IR spectrum and DT-TG profiles are given. Contradictions between the IR spectrum, a recent structural refinement and the DT-TG are discussed, but cannot be explained satisfactorily
Single-crystal polarized light IR study of an historical synthetic water poor emerald
No full textThis paper describes a single-crystal polarised-light FTIR study of the original emerald synthesised by HAUTEFEUILLE & PERREY (1888) using the flux method. The microchemical data show the analysed sample to be very close to the stoichiometric composition and homogeneous except for a significant variation in the Cr(2)O(3) content (from 1.45 to 2.59 wt%). Trace amounts of Ti. Mg. Fe. Zn. Na, K and F were also detected. The cell parameters are (in angstrom) a = 9.2264(25) and c = 9.1904(2), c/a = 0.9961. Despite the synthesis conditions, FTIR spectra in the OH-stretching region show the presence of weak but significant H(2)O vibrations in the crystals. The polarised FTIR spectra collected with E perpendicular to c consist of a unique sharp and intense band at 3643 cm(-1), whereas the E//c spectra consist of two minor bands at 3643 and 3587 cm(-1). These bands are assigned to the nu(3) antisymmetric stretching, and v, symmetric stretching modes of type 11 water in the structural channels, respectively. These water molecules are probably associated with Li impurities in the mineral, due to the flux employed for the syntheses. Using the molar absorption coefficient epsilon(i) = 27126 1 * mol(-1) * cm(-2) from the calibration curve of LIBOWITZKY & ROSSMAN (1997), a water content of similar to 30 ppm is derived for the studied emerald
Single-crystal polarized-light FTIR study of a historical synthetic water-poor emerald
No full textThis paper describes a single-crystal polarised-light FTIR study of the original emerald synthesised by Hautefeuille
& Perrey (1888) using the flux method. The microchemical data show the analysed sample to be very close to the stoichiometric
composition and homogeneous except for a significant variation in the Cr2O3 content (from 1.45 to 2.59 wt%). Trace amounts of
Ti, Mg, Fe, Zn, Na, K and F were also detected. The cell parameters are (in Å) a = 9.2264(25) and c = 9.1904(2), c/a = 0.9961. Despite
the synthesis conditions, FTIR spectra in the OH-stretching region show the presence of weak but significant H2O vibrations
in the crystals. The polarised FTIR spectra collected with E⊥c consist of a unique sharp and intense band at 3643 cm-1, whereas
the E//c spectra consist of two minor bands at 3643 and 3587 cm-1. These bands are assigned to the ν3 antisymmetric stretching,
and ν1 symmetric stretching modes of type II water in the structural channels, respectively. These water molecules are probably
associated with Li impurities in the mineral, due to the flux employed for the syntheses. Using the molar absorption coefficient
εi = 27126 l * mol-1 * cm-2 from the calibration curve of Libowitzky & Rossman (1997), a water content of ∼ 30 ppm is derived
for the studied emerald
Il giacimento di bentonite di Uri. Alcuni aspetti geologici, chimico petrografici e mineralogici
No full textIl giacimento di bentonite di Uri. Alcuni aspetti geologici, chimico-petrografici e mineralogici.
No full textPrimi risultati di uno studio qualitativo sulla bentonite di Uri affrontato da diversi punti di vista: geologico, petrografico, chimico e mineralogico. Ad una premessa generale sul vulcanismo sardo segue la descrizione geologica e giacimentologica dell'area di Pedra de Fogu; vengono quindi riportati i risultati di alcune analisi chimiche, petrografiche e diffrattometriche, in base alle quali è stato fatto un tentativo di correlazione tra alcuni parametri; in particolare vengono avanzate alcune ipotesi sulla relazione tra giacitura, composizione chimica e colore
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