65 research outputs found
Moganite occurrence in quartz varieties (Chalcedony and Carnelian) from Evros Region, NE Greece
No full textExtended Abstract
Samples of gem varieties of quartz from the Evros region in north-eastern Greece were
spectroscopically analysed to determine their micro- to cryptocrystalline mineralogical properties
using a Renishaw inVia micro-Raman microscope. The micro-Raman instrument provides point-andshoot
Raman capabilities with a spatial resolution of 1 μm integrated into a standard microscope. The
frequency shifts were calibrated with an internal Si reference sample.
Samples analysed included different types of quartz, such as chalcedony and carnelian. During the
micro-Raman analysis, the samples of chalcedony and carnelian showed different ratios of
quartz/moganite, indicating heterogeneous formation conditions. This observation indicates that
nanocrystalline to microcrystalline moganite is present in the quartz [1].
The bands at 465 (Si-O bending vibrations), 209 and 129 cm-1 (lattice vibrations) are the
characteristic bands of α-quartz [2]. The peak at 503 cm-1 corresponds to the symmetrical stretching
vibrations of the Si-O bonds in moganite. The proportion of moganite in the chalcedony was I503/I465
= ~25%, while it was particularly high in the carnelian samples with I503/I465 = ~35%. Both samples
show a weak band at 395 cm-1, which could indicate the presence of the Fe+3 - O vibrational mode,
possibly due to the colorant substance [3]. The peaks at 2851 and 2930 cm-1, which only occur in the
carnelian sample, correspond to the OH- vibrational modes. Τhe presence of moganite in SiO2 varieties has been interpreted as an indication of their formation
age. According to Lee et al., [4], the presence of moganite suggests that the SiO2 varieties are younger
than -100Ma. This fact is consistent with the available geochronological data for the formations
hosting the studied SiO2 varieties, which indicate an Oligocene age [5,6]. This is evidenced by the
transformation of thermodynamically unstable moganite into quartz, or by the dissolution process of
moganite during silica-water interactions at ambient pressure [6-9]. Moganite also exhibits a
relatively intense band at 463 cm–1 that overlaps with the main 465 cm–1 mode of quartz at 465 cm–1 while the 503 cm–1 peak of moganite shows no interference [10].
Moganite is a low-temperature precipitate that coexists with fine-grained quartz [4]. In Schmidt et
al. [9], the peak at 503 cm-1, of moganite is described as a temperature dependent vibration band that
tends to be shifted to lower Raman shifts at higher temperatures. The moganite-specific Raman band
was found exactly at a wavenumber of 503 cm-1 in the samples analysed in this study. Moganite
formation is associated with the presence of silanol in hydrothermal fluids. This is evident from our
Raman spectroscopy results, which show a proportion of quartz/moganite. In addition, Caggiani et
al., [11] suggest that a peak at 504 cm−1 also indicates the presence of silanol. Furthermore, the
occurrence of peaks at wavenumbers 2851 and 2930 cm-1 suggests the presence of OH- within the
quartz (var. carnelian) crystal structure. These observations not only confirm the presence of moganite
by the Si-O peak at 503 cm-1, but also indicate the presence of Si-OH- resulting from the hydrothermal
process, which requires silica-rich fluids known as silanol [12]. Lee et al., [4] found that carnelian is
formed mainly from a mixture of higher-temperature hydrothermal fluids and shallower, lowertemperature,
meteoric water. These were formed in Tertiary magmatic-hydrothermal environments
throughout Greece, more specifically in hydrothermally altered igneous rocks that host several silica
varieties, most of which yield gem- or semi-precious quality material [13]. The results presented here
correspond to the same statement confirmed by micro-Raman analysis. In addition, stability studies
of moganite during thermal treatment show that moganite disappears at high temperatures [11].
Similarly, moganite is observed as an intermediate phase in the diagenesis of permineralised fossil
wood [14], suggesting a hydrothermal influence on the rock at low temperatures. Based on all the
above, moganite could indicate a low-temperature precipitating mineral coexisting in relation to α-
quartz
First finding of microdiamond, coesite and other UHP phases in felsic granulites in the Moldanubian Zone: Implications for deep subduction and a revised geodynamic model for Variscan Orogeny in the Bohemian Massif
No full text
Groundwater Deterioration: The Simultaneous Effects of Intense Agricultural Activity and Heavy Metals in Soil
No full textAbstractGroundwater deterioration due to agricultural activity is mainly attributed to intense fertilization, groundwater overpumping and seawater intrusion being more pronounced in coastal areas. Irrigation return water is one of the main sources of aquifers enrichment and it is expected to become the main source due to the simultaneous reduction of the amount/frequency of precipitation for many areas in Greece and the Mediterranean. The reduction of groundwater quantity and the simultaneous deterioration due to enhanced concentrations of fertilizer residues, such as nitrates, is well documented. Moreover, heavy metals of both anthropogenic and natural origin may be present in soils where agricultural activity takes place. As a result, groundwater is enriched in soluble species of heavy metals and this enrichment is a serious problem added on top of the above mentioned problems of groundwater deterioration. The relationship between heavy metals mobilization from soils to groundwater and the content of irrigation return water in solutes that influence the generation rates and mobility of heavy metals soluble species are discussed in this work. Data from groundwater samples taken in Psachna, Evia, a region characterized by elevated geogenic Cr in soils and intense agricultural activity, are presented. Two aspects of the problem are discussed: 1. The intense use of ammonium fertilizers: The pH reduction from the nitrification of ammonium fertilizers may be a serious factor influencing Cr(III) mobility. 2. The role of the ionic strength of the water (enhanced concentrations of cations due to seawater intrusion in the aquifer) in the mobility of Cr(III) by mechanisms of cation exchange
Χαρακτηρισμός του Υποδοχέα της ιντερλευκίνης-2 σε μη -Τ λευχαιμικές σειρές
No full textΗ οξεία μη-Τ Λεμφοβλαστική Λευχαιμία, όπως αναφέραμε και σε προηγούμενο κεφάλαιο, είναι μια κακοήθης νεοπλασία προβαθμίδων των Β κυττάρων, που έχασαν την ικανότητα διαφοροποίησης. Πιστεύεται ότι το προπρο-Β κύτταρο, το οποίο έχει ξεκινήσει τη διαφοροποίηση του, βρίσκεται ξαφνικά κάτω από την επήρεια ενός αγνώστου λευχαιμογόνου παράγοντα, ο οποίος το αναγκάζει αφ΄ενός μεν να σταματήσει την περαιτέρω διαφοροποίηση του και αφ΄ετέρου να μην υπακούει στους φυσιολογικούς μηχανισμούς, που ρυθμίζουν τον πολλαπλασιασμό τους. Έτσι, το προ-Β κύτταρο, αρχίζει να πολλαπλασιάζεται ανεξέλεγκτα, για να δώσει ένα μεγάλο αριθμό λευχαιμικών κυττάρων. Προκειμένου να μελετήσουμε εάν ο πολλαπλασιασμός των νεοπλασματικών κυττάρων ασθενών με προ-Β Λεμφοβλαστική Λευχαιμία εξαρτάται από τη δράση ορισμένων λεμφοκινών και ιδιαίτερα από το σύστημα IL-2/IL-2R, διερευνήσαμε την έκφραση και τη λειτουργικότητα των δύο αλύσεων του υποδοχέα της IL-2(IL-2R) σε κύτταρα ασθενών με προ-B Λεμφοβλαστική Λευχαιμία, σε κύτταρα της Reh-6 προ-Β Λευχαιμικής σειράς και σε κύτταρα της λευχαιμικής σειράς ΝΟΙ-90. Η λειτουργικότητα των υποδοχέων της ΙL-2 μελετήθηκε με πειράματα ισορροπίας της δέσμευσης της ραδιοσημασμένης ΙL-2 στην κυτταρική μεμβράνη. Διερευνήσαμε τη δράση ορισμένων μιτογόνων και αναστολέων του πολλαπλασιασμού. Πιο συγκεκριμένα μελετήσαμε τη δράση του ΡΜΑ (Phorbol Myristate Acetate), όσον αφορά την έκφραση των αλύσεων του υποδοχέα της ΙL-2 στη μεμβράνη και σε μοριακό επίπεδο με σκοπό να καταλάβουμε καλύτερα το ρόλο του συστήματος ΙL-2/IL-2R στον πολλαπλασιασμό των προ-Β κυττάρων. Μελετήσαμε επίσης, η έκφραση του mRNA των δύο αλύσεων του υποδοχέα της ΙL-2. Η συγγένεια των υποδοχέων της ΙL-2 ελέγχθηκε με πειράματα συνδέσεις ραδιοσημασμένης με 125Ι, ανασυνδυασμένης ΙL-2 και ανάλυση κατά Scatchard. Η δομή του υποδοχέα μελετήθηκε με cross-linking της σημασμένης ΙL-2 στα κύτταρα, ηλεκτροφόρηση σε πήκτωμα πολυακρυλαμίδης και αυτοραδιογραφία. Η ειδικότητα των αντιδράσεων ελέγχθηκε με την αναστολή τους χρησιμοποιώντας τόσο ψυχρή ΙL-2 όσο και μονοκλωνικά αντισώματα, έναντι των ενεργών θέσεων των ΙL-2Rα και ΙL-2Rβ
A combined Raman, Fourier transform infrared, and X‐ray diffraction study of thermally treated nesquehonite
No full textGeotechnical properties of a natural zeolite
No full text An investigation into the geotechnical properties of a natural, crushed and ground zeolite used as a compacted soil liner in geoenvironmental applications was carried out to ensure adequate strength and permissible compressibility. Tests aimed at examining the influence of gradation, density and stress level on strength show that the zeolite behaves as any granular material with its shear strength in direct shear increasing with density and stress level and decreasing with increasing uniformity. To validate these findings direct shear tests were performed on two quartz sands of similar mean diameter and varying gradations and grain shape. The results of the tests on the zeolite and the sand of similar gradation and grain shape nearly coincide. For the zeolite under consideration, which is mainly composed of clinoptilolite, grain crushing is negligible for stress levels common in engineering construction. Finally, the influence of wetting on the shear strength of the zeolite is insignificant. The results indicate that these materials can be analysed within the framework of behaviour for quartz sands. </jats:p
On the Origin of Bastnaesite-(La,Nd,Y) in the Nissi (Patitira) Bauxite Laterite Deposit, Lokris, Greece
No full textA detailed geochemical study and a thorough mineralogical description of the rare-earth elements (REE)-minerals and associated minerals were carried out in two vertical profiles of approximately 4 m length, from the Nissi (Patitira) bauxite laterite deposit, Lokris, Greece, characterized by the presence of goethite in small sizes resembling bacterial cell coated by goethite and a significant REE enrichment. The enrichment of the REE concentrated in bastnaesite-group minerals, the intergrowths between REE-minerals and Al–Ni–silicates with significant sulfur contents and their association with goethite microtextures interpreted as bacteriomorphic, indicate REE remobilization along with iron bio-leaching and re-precipitation on karstified limestone. In addition to the previous-reported hydroxylbastnaesites, a (La,Nd,Y)(CO3)F member of the bastnaesite-group associated with Al–Ni–silicates were identified, the stability of which may reflect the dependence on the source rocks and the local variations of pH-Eh. Interaction between downward percolating water and carbonate rocks seems to be a very effective mechanism for REE fluorocarbonates deposition under alkaline and reducing conditions
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