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21.
Polarized infrared absorption spectra of thin single-crystal slabs parallel to (010) and (001) of a staurolite from Pizzo Forno, Ticino, with analyzed composition (Fe2.9Mg0.9Zn0.1Mn0.1)Al17.5Ti0.1(Si7.7Al0.3)O48H3 have been measured in the range of 3000–4000 cm?1. From the pleochroitic behaviour of the OH-vibrations three groups of bands can be distinguished: the bands of group I, a strong band at 3445 cm?1 plus a weak shoulder at 3358 cm?1, and the bands of group II, a weak band centered at 3677 cm?1 plus a shoulder at 3635 cm?1, are assigned to the H1 and H2 protons, respectively. The bands of group III, a weak band at 3577 cm?1 plus a shoulder, cannot be interpreted on the basis of the proton positions known so far. We assign them to an additional proton H3, which is bonded to O1 and shows a bifurcated hydrogen bridge to two O5 in a vacant T2 site. 相似文献
22.
Waterfowl and American coot data collected from aerial censusing on Currituck Sound were compared during three periods: before Eurasian watermilfoil (Myriophyllum spicatum) colonization (1961–1965); during Eurasian watermilfoil infestation (1968–1977); and following the near absence of submersed macrophytic vegetation after Eurasian watermilfoil decline (1981–1990). Numbers of dabbling ducks (Anas rubripes, Anas platyrhynchos, Anas acuta, Anas americana, Anas crecca), ring-necked ducks (Aythya collaris), and American coot (Fulica americana) were significantly different in Currituck Sound (p<0.05) in at least two of these periods and were highest during Eurasian watermilfoil infestation. These species also constituted higher percentages of the Atlantic Flyway counts during Eurasian watermilfoil infestation. than in periods before or after. Numbers of snow geese (Chen caerulescens), Canada geese (Branta canadensis), and canvasbacks (Aythya valisneria) were significantly different between periods; however, these birds exhibited a consistent decline from the early to the late period. This study suggests that submersed macrophytes, specifically Eurasian watermilfoil, support increased numbers of dabbling ducks, ring-necked ducks, and American coot. 相似文献
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Polarized infrared (IR) spectroscopy of olivine crystals from Zabargad, Red Sea shows the existence of four pleochroic absorption bands at 3,590, 3,570, 3,520 and 3,230 cm?1, and of one non pleochroic band at 3,400 cm?1. The bands are assigned to OH stretching frequencies. Transmission electron microscopy (TEM) shows no oriented intergrowths in this olivine; it is concluded that OH is structural. On the basis of the pleochroic scheme of the absorption spectra it is proposed that [□O(OH)3] and [□O2(OH)2] tetrahedra occur as structural elements, assuming that the vacancies are on Si sites. If M2 site vacancies were assumed [SiO3(OH)] and [SiO2(OH)2] tetrahedra occur as structural elements. 相似文献
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Anton P. Roex Andreas Späth Robert E. Zartman 《Contributions to Mineralogy and Petrology》2001,142(1):89-106
Geochemical data are reported for samples from the flanks and floor of the southern Kenya Rift Valley in the Lake Magadi area, and from two central volcanoes located within the rift valley. Rift lavas include samples of Singaraini and Ol Tepesi basalts on the eastern flank, Kirikiti basalts from the western flank, and plateau trachytes from the rift valley floor. Central volcano samples are from Ol Esayeiti and Lenderut located on the eastern flank. The rift basalts are mildly ne-normative, moderately evolved (Mg#=0.39-0.62) alkali basalts and show an overall range in differentiation. Incompatible trace element abundances are moderately elevated (Nb=17-51; Zr=93-274; La=17-55 ppm) and show strongly coherent variations and constant inter-element ratios (e.g. Zr/Nb=4.2-5.5; Nb/Ta=17.5ǂ.4; (La/Sm)n=7.3ǃ.1); isotope ratios are restricted in range (87Sr/86Sr=0.70393-0.70436; 143Nd/144Nd=0.51272-0.51280; 206Pb/204Pb=19.87-19.92; 207Pb/204Pb=15.68-15.70; 208Pb/204Pb=39.56-39.71). Central volcano lavas are more alkaline in character and include basanite (Ol Esayeiti; Mg# >60) and hawaiite to benmoreite (Lenderut; Mg#=0.48-0.38). Incompatible element ratio are similar to those of the rift basalts, although the chondrite normalised REE patterns are steeper (La/Sm)n=17.4ǃ.2). 87Sr/86Sr (0.70358, 0.70391), 143Nd/144Nd (0.51280, 0.51267), 206Pb/204Pb (19.96,20.17), 207Pb/204Pb (15.66,15.76) and 208Pb/204Pb (39.80,40.00) ratios of Ol Esayeiti basanites are similar to the rift basalts, whereas the Lenderut lavas have unusually low143Nd/144Nd (0.512388-0.512453) ratios for their 87Sr/86Sr (0.70370-0.70481) ratios, and distinctly less radiogenic and variable Pb isotope compositions (206Pb/204Pb=17.93-19.01; 207Pb/204Pb=15.43-15.58; 208Pb/204Pb=37.91-39.14). An integrated model is developed in which the geochemical signature of the lavas is attributed to variable degrees of melting to depths within the garnet stability field, and in the presence of residual amphibole. The stability fields of these phases in P-T space indicates that the lavas must have formed within the sub-continental lithosphere rather than within the underlying ambient asthenosphere or a rising mantle plume. The subcontinental lithospheric mantle must therefore extend to a depth of at least 75 km beneath the Lake Magadi area, which contrasts with recent gravity models for the area, which infer that lithospheric mantle is absent beneath this section of the southern Kenya Rift. 相似文献
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Anton Hammann 《Aquatic Sciences - Research Across Boundaries》1957,19(2):579-612
Ohne Zusammenfassung 相似文献
29.
Zusammenfassung Rutile, Cassiterite und Brookite verschiedener Fundorte enthalten entsprechend einer scharfen Absorptionslinie bei =3 kleine Mengen von Hydroxyl-Gruppen. Die Zuordnung der Absorptionslinie zur OH-Streckschwingung wurde für diese drei Minerale durch die Linienverschiebung bewiesen, die man nach hydrothermaler Deuterierung beobachtet. Die ungefähre Orientierung der OH-Gruppen konnte aus dem Pleochroismus orientierter Kristallplatten abgeleitet werden, wobei polarisierte UR-Strahlung verwendet wurde. Es wird die strukturelle Deutung gebracht. Anatas alpiner Herkunft enthält keine oder nur sehr wenige OH-Gruppen.
Mit 8 Abbildungen 相似文献
Measurement of the infrared-pleochroism in Minerals. XI. The Pleochroism of the OH-stretching frequency in rutile, anatase, brookite, and cassiterite
Summary Rutile, cassiterite, and brookite from several localities contain small amounts of hydroxyl groups, based on the presence of a sharp absorption line at =3. The attribution of the absorption line to the OH-stretching vibration is proved for the three minerals by the line shift which is caused by hydrothermal deuteration. The approximate orientation of the OH-groups could be derived from the pleochroism as observed in oriented crystal plates with polarized IR-radiation. The structural interpretations are given. Anatase, however, from Alpine fissures contains no or undedectable amounts of OH-groups.
Mit 8 Abbildungen 相似文献
30.
Zusammenfassung Mikroskopisch Einschluß-freie Andalusite aus Brasilien zeigen im UR-Absorptionsspektrum ein Doppelmaximum bei zirka 2,9 und ein deutlich schwächeres einfaches Maximum bei 3,04 , die OH-Valenzschwingungen zugeordnet werden. Diese Maxima verschwinden nach mehrtägigem Glühen bei 1000° C. In Platten parallel (110) zeigt das Doppelmaximum bei zirka 2,9 einen extrem starken Pleochroismus, wobei die Bande praktisch völlig verschwindet, wenn der elektrische Vektor parallel [001] schwingt. Damit müssen zumindest die OH-Gruppen, die für diese Bande verantwortlich sind, in die Struktur eingebaut sein. Für beide Arten von OH-Gruppen werden die plausiblen Anordnungen diskutiert.
Mit 3 Abbildungen 相似文献
Measurement of the infrared-pleochroism in minerals. VIII. The pleochroism of the OH-stretching frequency in andalusite
Summary Inclusion-free andalusites from Brazil show in the IR absorption spectrum a double maximum at ca. 2.9 and a much weaker single maximum at 3.04 which are interpreted as belonging to OH-stretching frequencies. The maxima disappear after annealing the specimen at 1000°C for several days. Plates parallel to (110) show a very strong pleochroism for the 2.9 -band, the peak being practically of zero height if the electric vector vibrates parallel [001]. This proves that at least the OH-groups which are responsible for this absorption band are constituents of the crystal structure. For both kinds of OH-groups the probable distributions are discussed.
Mit 3 Abbildungen 相似文献