1,720,984 research outputs found
Crystal chemistry of clinopyroxenes in spinel-peridotite mantle xenoliths from the Fernando de Noronha oceanic island (NE-Brazil).
No full textInclusi ultramafici di una camptonite di Predazzo: termometria e barometria degli inclusi di mantello.
No full textClinopyroxene of spinel peridotite mantle xenoliths from Lake Nji (Cameron Volcanic Line, W Africa): crystal chemistry and petrological implications.
No full textIndagini archeometriche su vetri romani e medievali
No full textRiassunto presentato al III Congresso Nazionale AIAr "L'Archeometria in Italia: la Scienza per i Beni Culturali", Bressanone, 11-12 febbraio 2004
Inter- and intra-crystalline temperature and pressure estimates on pyroxenes from NE Brazil mantle xenoliths.
No full textMercier's thermobarometer (Mercier 1980) and Saxena's thermometer (Dal Negro et al. 1982) were applied to single pyroxenes of both porphyroclastic (PF) and protogranular (PR) spinel peridotitic nodules enclosed in alkaline products related to necks of North-Eastern Brazil. Intercrystalline temperatures obtained using both orthopyroxene (opx) and clinopyroxene (cpx) compositions were in agreement, and were lower in protogranular than in porphyroclastic nodules (1051_+57 and 1266 +_ 19~ respectively). In contrast, pressure estimates using cpx and opx were conflicting, in particular as
regards PF nodules. In fact for PF nodules cpx compositions
point to 27 32 kbar (mean 29_+2) whereas opx compositions point to 1%19 kbar (mean 18_+ 1). Conversely, PR nodule cpx and opx compositions point to similar values 17 24 and 15-18 kbar respectively (mean 19_+4). The result obtained for PF nodules using cpx composition clearly contrasts with petrographic evidence
and it is due to the peculiar composition of PF cpx (e.g. low Ca content, from 0.645 to 0.737 atoms per formula
unit, a.f.u.) that strongly affects the barometric formulation.
The PR and PF cpxs reveal similar mean intracrystalline
temperature estimates (712 _+ 112 and 778 +_ 217~
respectively). These, considering the difference of about
200~ in the intercrystalline temperature estimates, indicate
that the exchange cation reaction between the M1
and M2 sites was a faster process in PF than in PR cpx,
favoured by the low Ca content of PF cpx. Thus alternatively,
the composition of PF cpx, characterized by a high
rate of Ca ~ Mg substitution in the M2 site, may not
affect the intercrystalline temperature. Therefore the difference
of about 200~ found in intercrystalline temperatures
between PR and PF cpxs, in spite of their same
pressure values, may be interpreted as indicating an
anomalous temperature gradient in the region
Crystal Chemistry of the constituent phases of a spinel peridotite nodule from Cameroon volcanic line (W-Africa).
No full textColloidal precipitates related to AMD settings: a combined HT-XRD and bulk leaching test approach.
No full textColloidal maghemite nanoparticles with oxyhydroxide-like interface and chiroptical properties
No full textMagnetic nanoparticles, mainly constituted of magnetite and maghemite, are widely used for environmental, biomedical and biotechnological applications. Herein, the synthesis and properties of maghemite nanoparticles characterized by chiroptical activity, representing an unprecedented feature for iron oxide nanoparticles, is described in detail. Among nanosized iron oxides, these maghemite nanoparticles stand out for the excellent colloidal stability in water and the witnessed ability to specifically bind selected molecules. The surface properties of nanoparticles were probed with AsIII and AsV oxyacids, studied by x-ray photoelectron spectroscopy and correlated to circular dichroism. The dichroic signal of nanoparticles was differently influenced by the coordination of ligands. Crystalline vacancies on the nanomaterial surface were identified as the chiral centers responsible of the dichroic behavior and the selectivity toward ligands. The latter was correlated with the ability of restructuring the nanomaterial at the crystal truncation. Furthermore, surface binding sites emerged for bearing labile coordination water in analogy with iron oxyhydroxides. The present report, besides enriching the colloidal chemistry of iron oxide based nanomaterials, can stimulate further research on inorganic systems expressing intrinsic chiral properties
Le sabbie per la produzione di vetro in epoca romana: una nuova prospettiva sulle fonti di approvvigionamento
No full textRiassunto presentato al Congresso FIST GEOITALIA 2003, Forum Italiano di Scienze della Terra, Bellaria (Rimini, Italia), 16-18 settembre 2003
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