1,720,981 research outputs found
MOSANDRITE: STRUCTURAL AND CRYSTAL-CHEMICAL RELATIONSHIPS WITH RINKITE
No full textemical (EPM data), TG–DSC studies and structural investigations indicate that mosandrite presents a particular chemical
composition (low Ca, Na and F contents, high amount of H2O), unit-cell parameters (a 7.398, b 5.595, c 18.662 Å, b 101.37°,
V 757.29 Å3; space-group symmetry P21/c; Z = 2), and a rinkite-type structure characterized by a low occupancy of the M(2) and M(3) sites
Chemical and structural study of the Zr,Ti-disilicates in the venanzite from Pian di Celle, Umbria, Italy
No full textCuspidine and götzenite were found as accessories in the pegmatitoid facies of venanzite from the Pleistocene lava flow of Pian di Celle. The modal compositions of venanzite and its pegmatitoid facies have been defined through combined XRF and Rietveld quantitative analyses. Cuspidine and götzenite were unambiguously identified by combining microprobe analyses and structural studies. The structure analyses werecarried on with single-crystal XRD data and the refinements converged to R1 = 0.048 and 0.053 for cuspidine and götzenite respectively. Cuspidine from Pian di Celle, ideally (Ca,Zr) Ca2 (Ca,Na) Si 2O7 F2, Z = 4, space group P2 1/a, a = 10.919(2), b = 10.485(1), c = 7.485(1) Å , β = 109.55(1)°, represents a Zr,Na-rich variety of cuspidine. Götzenite from Pian di Celle, ideally (Ca,Zr) (Ca,Na) Ca (Na,Ca) 0.5 Ti0.5 Si2O7 (F,OH,O)2, Z = 2, space group P1, a = 9.636(3), b = 7.341(2), c = 5.737(1) Å, α = 89.94(2), β = 100.74(2), γ = 101.06(3)°, represents a Zr-rich variety of götzenite. Zirconium and sodium enter in the structures substitutingpart of calcium, according to the main substitution indicated by the chemical data: 2Ca2+ + F- ↔ Na+ + (Zr+Ti)4+ + O2-
Distinct domains in guarinite from Monte Somma, Italy: crystal structures and crystal chemistry.
No full texttract“Guarinite” is a typical accessory mineral of the Monte Somma syenite; it belongs to the cuspidine group and displays a domain structure. “Guarinite” contains up to three distinct domains, corresponding to three different ways to connect disilicate groups and walls of octahedra; these may all be simultaneously present in the same crystal. The domains present in the crystals of “guarinite” have cell type I, II and IV, according to the classification scheme proposed for cuspidine-group minerals. Domain IV is the most common, and domain I is the rarest; domain II may occur as the only domain, whereas domain I occurs only in association with domain IV, which invariably predominates. So far, the actual structure of the various domains had not been defined. EPMA and single-crystal structural studies indicate that domain I of “guarinite” displays space group P1, with a 10.973(2), b 10.306(1), c 7.367(3) Å, a 90.03(3), b 109.63(3), g 90.11(2)°, with a crystal-chemical formula Ca3(Ca0.72
Zr0.28)S1.00(Zr0.86M0.14)S1.00(Ca0.59Mn0.25Fe0.16)S1.00(Na1.20Ca0.76)S1.96(Si1.98O7)2(F2.88O1.12)S4.00, where M represents Nb, Ti, Al, Sr, and REE. Domain I is isostructural with hiortdahlite II, and its crystal structure was refined to a final R of 0.072. Domain II of “guarinite” displays space group P1211, with a 10.836(1), b 10.270(1), c 7.296(1) Å, b 109.13(3)°, with a crystal-chemical formula Ca3Zr(Nb0.56Fe0.15Mn0.10Ti0.10Zr0.09)S1.00(Ca0.72Mn0.18M0.10)S1.00(Na0.77Ca0.23)S1.00(Na0.80Ca0.22)S1.02(Si2O7)2(O2.17
F1.83)S4.00, where M represents Al, Mg, Sr and Y. Domain II is isostructural with wöhlerite, and its crystal structure was refined to a final R of 0.045. Domain IV of “guarinite” adopts space group P1, with a 10.970(2), b 10.943(2), c 7.365(1) Å, a 109.63(2), b 109.65(2), g 83.39(1)°, with a crystal-chemical formula Ca4Zr(Ca0.31Mn0.25Fe0.16Zr0.14M0.14)S1.00(Na1.20
Ca0.76)S1.96(Si1.98O7)2(F2.88O1.12)S4.00, where M represents Nb, Ti, Al, Sr and REE. Domain IV is isostructural with hiortdahlite I, and its crystal structure was refined to a final R of 0.067. One should note that the refinements of domain I and domain IV (both twinned) have been carried out on the same crystal. EMPA and SEM studies show the presence of chemically homogeneous crystals as well as crystals with distinct chemical zoning due to a wide variation of the major elements Nb, Ca, Na, F, and pointing to the possible coupled substitution Nb5+ + 2Na+ + O2– →← 3Ca2+ + F– as one of the main mechanisms of chemical variation
«Johnstrupite »: a chemical and structural study
No full textChemical (EPM analyses), crystallographic and structural (single crystal X-Ray diffraction) investigations carried out on a specimen of "johnstrupite" from the Barkevik skerry, taken from Brøgger's own collection, pointed to its identity with rinkite and indicated the ideal crystal chemical formula Ti(Na2Ca)(Ca3REE)(Si2O7)2(F3O)
Open source WEB applications for spatial data management and for water resource analysis
No full textMany problems of water resource management are strongly related to their spatial distribution and due to a use that is usually uncontrolled, such as water withdrawals. For these reasons, web procedures have been developed in order to manage spatial data of interest and to analyze information on water resources, so that this tool can be widely used and shared freely and easily by all stakeholders.
A prototype of this instrument is the web tool "Water Resources Management and Evaluation" (WRME). The main features of this project can be summarized as follows:
- is easy to use, both for the database like and the map-based consultation;
- uses synthetic indicators simplifying the hydrological and hydraulic information;
- integrates tools for the update and the exchange of data between different databases of different stakeholders;
- integrates the possibility to implement and update, in a distributed manner over the basin and the drainage network, all constraints arising from the different legislations and management plans;
- provides synthetic information on the sustainability of scenarios;
- provides synthetic information on the sustainability of new water withdrawals;
- software is open source, therefore economic resources can be invested on training and development.
The methodology of this project can also be applied in other areas of sustainable management of environmental resources
Impact of climate change on the hydrology and the sponge population of the shallow Lake Trasimeno (Umbria, Italy): history, forecasting and management
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