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Crystal chemistry of Mg-, Fe-bearing muscovites-2M(1)
No full textPhengitic muscovite-2M(1), crystals [([12])(K0.88-0.99Na0.01-0.09Ca0.Ba-00-0.06(0.00-0.01))([6])(Al1.64-1.88Fe0.06-0.292+Fe0.01-0.163+Mg0.00-0.16Mn0.00-0.07Ti0.00-0.06)([4])(Si2.87-3.30Al0.70-1.13)(OH)(1.56-2.07)F0.00-0.41O9.91-10.25] from peg matites and peraluminous granites were refined to investigate the influence of phengitic substitution on the mica structure. Single-crystal X-ray diffraction data were collected for eleven crystals in the C2/c space-group (agreement factor 2.1% less than or equal to R-obs less than or equal to 3.9%). Tetrahedral Si and Al cation disorder was found for each sample, with the mean tetrahedral cation-oxygen distances ranging from 1.639 Angstrom less than or equal to less than or equal to 1.647 Angstrom and 1.640 Angstrom less than or equal to less than or equal to 1.646 Angstrom. As phengitic substitution increases, the octahedral sheet expands and requires a less distorted (more hexagonal) tetrahedral ring (7.70 degrees less than or equal to alpha less than or equal to 11.38 degrees) and low corrugation of the basal O plane (0.1796 Angstrom less than or equal to Delta z less than or equal to 0.2296 Angstrom). The electron density at the M2 site is greater than that required for the ideal muscovite-2M(1), structure, and a small excess of electron density is found in the M1 site. The inner sixfold coordination of the interlayer (A) cation is elongated along c*, which is consistent with the high or values and the long A-O11 bond length
Factors affecting the transport and recovery of heavy metals and organic pollutants in smectitic soils
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Crystal chemistry of Al-rich biotites coexisting with muscovites in peraluminous granites
No full textA comparison was made between single-crystal structure refinements, electron microprobe analy ses and octahedral site populations of seven biotite crystals and data obtained previously for coexisting muscovite in peraluminous granites using the same methods. Both micas, From several plutons of Northern Victoria Land (Antarctica) and Sardinia (Italy), show significant octahedral substitutions: biotite has a composition characterized by relatively high Al-[6] content (0.32 less than or equal to Al-[6] less than or equal to 0.59 apfu), whereas muscovite is characterized by phengite-like substitutions [0.12 less than or equal to ([6])(Mg + Fe + Ti + Mn) less than or equal to 0.35]. Mean bond-lengths and electron count data for six biotites-1M (space group C2/m. agreement factor 2.7% less than or equal to R-obs less than or equal to 3.6%) and a biotite-2M(1) (space group C2/c, R-obs = 2.8%) show that Al substitutes for divalent cations in the octahedral M2 site and that the Fe and Mg distribution is disordered. The mean tetrahedral bond lengths determined for biotite-2M(1) reflect Al-Si disorder. In coexisting muscovite-2M(1) crystals, small positive electron density residuals close to M1 site position as well as the increase in M2 mean atomic number is in agreement with the presence of a significant phengitic component. Reduction in biotite unit-cell dimensions with the increase of Al follows a pattern similar to that of associated muscovites. and the octahedral site volumes of both micas are influenced by the Al saturation index (ASI) of the rock. These results, and the calculated partition coefficients between biotite and muscovite for elements in M sites, are consistent with continuous reaction and re-equilibration of biotite and muscovite during crystallization of peraluminous granitic melts
Comparison between zeolite and sepiolite in the treatment of heavy metal polluted waters
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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