1,721,133 research outputs found
87Sr/86Sr Isotopic characterisation of dolina soils and flysch from Trieste area (NE Italy)
No full textDetrital pyroxenes in the Eocene flysch of the Istrian Basin (Slovenia, Croatia)
Full text linkFor the first time, few detrital augite and pigeonite crystals have been found in the Eocene flysch basins of Istria (Trieste-Koper basin; Italy, Slovenia, Croatia) and Krk Island (Croatia). Their chemistry suggests that they are related to subalkaline rocks (within-plate tholeiites) crystallized at a pressure between 0 and 5 kbar. As a possible source, the nearby basaltic andesites of Ljubac have been taken into consideration. The argument for a ?Late Tertiary age of the Ljubac volcanics is that no detrital pyroxenes have been found in the Eocene flysch and Oligo- Miocene molasse deposits of the area (Lugovic et al., 1998). Radiometric data are not available until now. The detection of detrital pyroxene could be an indication of an older age of the Ljubac volcanics. The presence of similar pyroxenes in the Trieste-Koper and the Krk Island flysch and their absence in Brkini flysch suggest that the basin of Krk was linked with the Istrian basin rather than the Brkini basin
Litotipi bauxitici dell’isola di Krk (Baška e Stara Baška – Croazia)
Full text linkVengono descritti i litotipi bauxitici rinvenuti nel corso di una ricerca condotta nella parte meridionale dell’isola di Krk (Dalmazia settentrionale – Croazia) nelle località di Baška e Stara Baška. Si tratta di rocce residuali, spesso compatte e di elevato peso specifi co, ricche di ossidi ed idrossidi di alluminio e ferro.
La ricerca è stata condotta sul campo ed in laboratorio, al fi ne di comprendere meglio i rapporti che intercorrono con le rocce calcaree incassanti e con il fenomeno carsico presente nell’area
First occurrence of titanomagnetites from the websterite dykes within Balmuccia peridotite (Ivrea-Verbano zone): Crystal chemistry and structural refinement
No full textThe crystal chemistry of three ulvöspinels from the websteritic dykes within the Balmuccia peridotites has been investigated by means of X-ray single crystal diffraction and electron microprobe. They are very similar each other with cell edge about 8.43 Å and oxygen positional parameter between 0.2565 and 0.2570. Ti content is about 0.32 a.p.f.u..As they are embedded in a glass with syenite composition it is supposed they quenched during the rapid cooling of a melt pervading the websteritic dykes. This is the first finding of similar spinels in the studied area
Structural changes in the FeAl2O4 - FeCr2O4 solid solution series and their consequences on natural Cr-bearing spinels
No full textThe influence of Al - Cr substitution on the spinel structure was studied in synthetic single crystals belonging to the FeCr2O4–FeAl2O4 series produced by flux growth at 1000–1300 °C in controlled atmosphere. Samples were characterized by single-crystal X-ray diffraction, electron microprobe analyses, and Mössbauer spectroscopy. Crystals of sufficient size and quality for single-crystal X-ray diffraction were obtained in the ranges Chr0-0.45 and Chr70-100 but not for intermediate compositions, possibly due to a reduced stability in this range. The increase in chromite component lead to an increase of the cell edge from 8.1534 (6) to 8.3672 (1) Å and a decrease in the u parameter from 0.2645 (2) to 0.2628 (1). Chemical analyses show that Fe2+ is very close to 1 apfu (0.994-1.007), Al is in the range 0.0793-1.981 apfu, Cr between 0 and 1.925 apfu. In some cases Fe3+ is present in amounts up to 0.031 apfu. Spinels with intermediate Cr content (Chr component between 40 and 60) are strongly zoned with Cr-rich cores and Cr-poor rims. Mössbauer analyses on powdered spinels of the runs from which single crystal have been used for X-ray structural data show values of Fe3+/Fetot consistently larger than that calculated by EMPA on single crystals, presumably due to chemical variation between single crystals from the same runs. The synthesis runs ended at a temperature of 1000°C, but it possible that cation ordering continued in the Cr-poor samples towards lower temperatures, possibly down to 700°
The crystal chemistry of detrital chromian spinel from the Southeastern Alps and Outer Dinarides: the discrimination of supplies from areas of similar tectonic setting?
No full textChromian spinel is a common heavy mineral in the fl ysch basins of the southeastern Alps and Outer Dinarides. Various
tectonic settings have been found for the suites of chromian spinel studied herein, related to suprasubduction for both Internal
and Outer Dinarides, and ocean-fl oor-spreading zones for the Outer Dinarides. Because the composition of the chromian spinel
cannot discriminate between the two areas, we performed crystallochemical studies in order to fi nd some differences. These
studies show that it is possible to discriminate between the suprasubduction zones of the Outer and Inner Dinarides by means of
the positional parameter u of the oxygen atom, which is close to 0.2625 for spinel grains from Outer Dinarides and greater than
0.2626 for spinel grains from Inner Dinarides. Intracrystalline temperatures ranging from 790 to 1050°C have been calculated
for spinels with u close to 0.2625, and 730 to 750°C for those with u higher than 0.2626. These temperatures are consistent with
those calculated for Outer and Inner Dinarides, respectively
Raman study of MgCr2O4 - Fe2+Cr2O4 and MgCr2O4-MgFe3+2O4 synthetic series: the effects of Fe2+ and Fe3+ on Raman shifts
No full textTwo synthetic series of spinels, MgCr2O4–
Fe2+Cr2O4 and MgCr2O4–MgFe23+O4 have been studied by Raman spectroscopy to investigate the effects of Fe2+ and Fe3+ on their structure. In the first case, where Fe2+ substitutes Mg within the tetrahedral site, there is a continuous and monotonic shift of the Raman modes A1g and Eg toward lower wavenumbers with the increase of the chromite component into the spinel, while the F2g modes remain nearly in the same position. In the second series, for low Mg-ferrite content, Fe3? substitutes for Cr in the octahedral site; when the Mg-ferrite content nears 40 %, a drastic change in the Raman spectra occurs as Fe3? starts entering the tetrahedral site as well, consequently pushing Mg to occupy the octahedral one. The Raman spectral region between 620 and 700 cm-1 is associated to the octahedral site, where three peaks are present and it is possible to observe the Cr–Fe3+ substitution and the effects of order–disorder in the tetrahedral site. The spectral range at 500–620 cm-1 region shows that there is a shift of modes toward lower values with the increase of the Mgferrite content. The peaks in the region at 200–500 cm-1, when observed, show little or negligible Raman shift
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