<Superscript>57</Superscript>Fe Mössbauer spectroscopy,X-ray single-crystal diffractometry,and electronic structure calculations on natural alexandrite     

Sven-Ulf Weber  Michael Grodzicki  Werner Lottermoser  Günther J. Redhammer  Gerold Tippelt  Johann Ponahlo  Georg Amthauer 《Physics and Chemistry of Minerals》2007,34(7):507-515

Natural alexandrite Al₂BeO₄:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The ⁵⁷Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe³⁺ and Fe²⁺, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe³⁺ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe³⁺ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe³⁺ on M1.  相似文献   

<Superscript>57</Superscript>Fe Mössbauer measurements and electronic structure calculations on natural lawsonites     

S.-U. Weber  M. Grodzicki  C. A. Geiger  W. Lottermoser  G. Tippelt  G. J. Redhammer  M. Bernroider  G. Amthauer 《Physics and Chemistry of Minerals》2007,34(1):1-9

Three natural lawsonites from Syke Rock, Mendocino Co., Reed Ranch, Marin Co., and Blake Gardens, Sonoma Co., all from the Coast Range Region in California, were studied by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe analysis, and X-ray powder diffraction. The samples contain about 0.6, 1.0, and 1.4 wt% of total iron oxide, respectively. ⁵⁷Fe Mössbauer spectra are consistent with the assumption that high-spin Fe³⁺ substitutes for Al in the octahedrally coordinated site. The Mössbauer spectrum of lawsonite from Syke Rock exhibits a second doublet with ⁵⁷Fe hyperfine parameters typical for octahedrally coordinated high-spin Fe²⁺. Electronic structure calculations in the local spin density approximation yield quadrupole splittings for Fe³⁺ in quantitative agreement with experiment indicating, however, that substitution of Al by Fe³⁺ must be accompanied by local distortion around the octahedral site. Model calculations also reproduce the room temperature hyperfine parameters of ferrous high-spin iron assuming the substitution of Ca by Fe²⁺. However, it cannot be excluded that Fe²⁺ may occupy a more asymmetric site within the microstructural cavity occupied by Ca and a H₂O molecule.  相似文献   

反射光谱技术:研究南极企鹅古生态演化的一种新方法   总被引：2，自引：0，他引：2  

孙静  刘晓东  孙立广  刘文齐 《极地研究》2007,19(3):203-212

为探求快速、廉价、无损和同步的光谱技术在南极生态环境研究中的可能性,本文利用南极阿德雷岛的四根企鹅粪土沉积柱样品的反射光谱,通过逐步多元线性回归和主成分回归两种数学运算方法,建立了反射光谱数据与企鹅粪九种标型元素浓度之间的关系,并探讨了南极企鹅粪土沉积物光谱数据的古生态意义。结果表明:南极粪土沉积样品反射率光谱与企鹅粪九种标型元素(P、Ca、Cu、F、Ba、S、Zn、Sr、Se)含量之间存在良好的相关性,预测值与实测值之间的相关系数R都达到了0.9以上,在深度剖面上预测浓度与实测浓度具有非常一致的变化趋势;南极粪土沉积物光谱数据包含有明确的古生态变化信息,可利用主成分分析快速恢复历史时期企鹅数量演化过程。本研究结果为在偏远的南极地区开展古生态环境研究提供了一种新的快捷方法和技术途径。  相似文献   

Analysis of Physical and Chemical Parameters for Discrimination of Water Origin in a Hydroelectric Reservoir     

Wagner José Barreto  Ieda Scarminio  Maria Cristina Solci  Dílson Norio Ishikawa  Melissa Tiemi Ogasawara  Sônia Naomi Nomi  Sônia Regina Giancoli Barreto 《洁净——土壤、空气、水》2007,35(3):239-245

Seventeen physical and chemical parameters were obtained from a hydroelectric reservoir located in a tropical region in the south of Brazil. Multivariate Principal Component Analysis (PCA) and Hierarchical Group Analysis (HGA) were used to identify the parameters discriminating the origin of water from the Tibagi and the Primeiro de Maio River, after it has passed the mixing region. The study was conducted during the dry and rainy seasons in July 2002 and February 2003 at three depths and three sampling sites located 0, 5, and 10 km away from the mixing region. The statistical methods showed to be appropriate for identifying the contribution of each tributary in the water mixing site of a complex water system. The most important discriminating parameter was the absorbance relation A(253 nm)/A(203 nm), followed by the concentrations of Fe(III), Mn(III), and Ni(II). An anthropogenic interference was found in the reservoir due to high Ni(II) and orthophosphate concentrations caused by a nearby town sewage discharge. The interference was more important during the dry periods due to the lower dispersion of the pollutants. Urgent initiatives should be taken from the state government to build treatment stations for the wastewater of the small cities around the Capivara hydroelectric reservoir to prevent the drinking water quality from deteriorating.  相似文献   

Use of high spectral resolution remote sensing to determine leaf palatability of eucalypt trees for folivorous marsupials     

Steve Dury  Brian Turner  Bill Foley  Ian Wallis 《International Journal of Applied Earth Observation and Geoinformation》2001,3(4):328

In this study we assess the feasibility of remotely measuring canopy biochemistry, and thus the potential for conducting large-scale mapping of habitat quality. A number of studies have found nutrient composition of eucalypt foliage to be a major determinant of the distribution of folivorous marsupials. More recently it has been demonstrated that a specific group of secondary plant chemicals, the diformylphloroglucinols (DFPs), are the most important feeding deterrents, and are thus vital determinants of habitat quality. We report on the use of laboratory spectroscopy to attempt to identify one such DFP, sideroxylonal-A, in the foliage of Eucalyptus melliodora, one of the few eucalypt species browsed by folivorous marsupials. Reflectance spectra were obtained for freeze-dried, ground leaves using near infrared spectroscopy (NIRS) and for both oven-dried and fresh whole leaves using a laboratory-based (FieldSpec) spectroradiometer. Modified partial least squares (MPLS) regression was used to develop calibration equations for sideroxylonal-A concentration based on the reflectance spectra transformed as both the first and second difference of absorbance (Log 1/R). The predictive ability of the calibration equations was assessed using the standard error of calibration statistic (SECV). Coefficients of determination (r²) were highest for the ground leaf spectra (0.98), followed by the fresh leaf and dry leaf spectra (0.94 and 0.87, respectively). When applied to independent validation sub-sets, sideroxylonal-A was most accurately predicted from the ground leaf spectra (r² = 0.94), followed by the dry leaf and fresh leaf spectra (0.72 and 0.53, respectively). Two spectral regions, centred on 674 nm and 1394 nm, were found to be highly correlated with sideroxylonal-A concentration for each of the three spectral data sets studied. Results from this study suggest that calibration equations derived from modified partial least squares regression may be used to predict sideroxylonal-A concentration, and hence leaf palatability, of Eucalyptus melliodora trees, thereby indicating that the remote estimation of habitat quality of eucalypt forests for marsupial folivores is feasible.  相似文献   

Location and quantitative analysis of OH in coesite     

M. Koch-Müller  Y. Fei  E. Hauri  Z. Liu 《Physics and Chemistry of Minerals》2001,28(10):693-705

 The incorporation of hydrogen (deuterium) into the coesite structure was investigated at pressures from 3.1 to 7.5 GPa and temperatures of 700, 800, and 1100 °C. Hydrogen could only be incorporated into the coesite structure at pressures greater 5.0 GPa and 1100 °C . No correlation between the concentration of trace elements such as Al and B and the hydrogen content was observed based on ion probe analysis (1335 ± 16 H ppm and 17 ± 1 Al ppm at 7.5 GPa, 1100 °C). The FTIR spectra show three relatively intense bands at 3575, 3516, and 3459 cm⁻¹ (ν₁ to ν₃, respectively) and two very weak bands at 3296 and 3210 cm⁻¹ (ν₄ and ν₅, respectively). The band at 3516 cm⁻¹ is strongly asymmetric and can be resolved into two bands, 3528 (ν_2a) and 3508 (ν_2b) cm⁻¹, with nearly identical areas. Polarized infrared absorption spectra of coesite single-crystal slabs, cut parallel to (0 1 0) and (1 0 0), were collected to locate the OH dipoles in the structure and to calibrate the IR spectroscopy for quantitative analysis of OH in coesite (ɛ _{i ,tot}=190 000 ± 30 000 l mol⁻¹ _H2O cm⁻²). The polarized spectra revealed a strong pleochroism of the OH bands. High-pressure FTIR spectra at pressures up to 8 GPa were performed in a diamond-anvil cell to gain further insight into incorporation mechanism of OH in coesite. The peak positions of the ν₁, ν₂, and ν₃ bands decrease linearly with pressure. The mode Grüneisen parameters for ν₁, ν₂, and ν₃ are −0.074, −0.144 and −0.398, respectively. There is a linear increase of the pressure derivatives with band position which follows the trend proposed by Hofmeister et al. (1999). The full widths at half maximum (FWHM) of the ν₁, ν₂, and ν₃ bands increase from 35, 21, and 28 cm⁻¹ in the spectra at ambient conditions to 71, 68, and 105 in the 8 GPa spectra, respectively. On the basis of these results, a model for the incorporation of hydrogen in coesite was developed: the OH defects are introduced into the structure by the substitution Si^4+(Si2)+4O²⁻= ^[4]□^(Si2) + 4OH⁻, which gives rise to four vibrations, ν₁, ν_2a, ν_2b, and ν₃. Because the OH(D)-bearing samples do contain traces of Al and B, the bands ν₄ and ν₅ may be coupled to Al and/or B substitution. Received: 19 December 2000 / Accepted: 23 April 2001  相似文献   

Characterisation of tobelite (NH4)Al2[AlSi3O10](OH)2 and ND4-tobelite (ND4)Al2[AlSi3O10](OD)2 using IR spectroscopy and Rietveld refinement of XRD spectra     

D. E. Harlov  M. Andrut  B. Pöter 《Physics and Chemistry of Minerals》2001,28(4):268-276

Tobelite (NH₄) Al₂ [AlSi₃O₁₀] (OH)₂, the ammonium analogue of muscovite, and its deuterated form ND₄-tobelite (ND₄) Al₂ [AlSi₃O₁₀] (OD)₂ have been synthesised at 600?°C and 200 and 500 Mpa using a well homogenised, stoichiometric SiO₂-Al₂O₃ oxide mix with Al₂O₃ in excess of 5 mol% and a 25% NH₃ solution whose relative abundance was such that the amount of NH₄ ⁺ stoichiometrically available was in excess of 50%. Characterisation of both tobelite and ND₄-tobelite using IR-spectroscopy, Rietveld refinement of X-ray powder diffraction data, and electron microprobe analysis indicate that, similar to K⁺ in muscovite, the NH₄ ⁺ or ND₄ ⁺ molecule occupies the interlayer site. IR absorption bands caused by NH₄ ⁺ and ND₄ ⁺ can be explained, to a very good approximation, on the basis of T_d symmetry. Nevertheless, substantial line broadening and the occurrence of shoulders indicate a deviation from ideal T_d symmetry. However, even at 77?K, no discrete splitting of the degenerate states could be confirmed. The OH stretching frequencies observed for synthetic tobelite are quite similar to those for muscovite, indicating that the replacement of K⁺ by NH₄ ⁺ has no effect. The low FWHH of the OH bands indicate that the hydroxyl groups are well ordered within the structure. Rietveld refinement of tobelite and ND₄-tobelite indicates that all samples synthesised consist of the 3 different mica polytypes which are typical of muscovite – namely 1M (C2/m), 2M ₁ (C2/c) and 2M ₂ (C2/c). Tobelite and ND₄-tobelite synthesised at 500 Mpa principally contain the 1M polytype, whereas the principle polytype for ND₄-tobelite synthesised at 200 Mpa, is 2M ₂. Rietveld refinement of X-ray diffraction spectra for tobelite synthesised at 200 Mpa was problematic due to the very broad FWHH of the X-ray peaks indicating poor crystallinity. In comparision to synthetic muscovite, the cell dimensions observed for tobelite and its deuterated analogue are quite similar except for the lattice constant c. Due to the larger radius of NH₄ ⁺ or ND₄ ⁺ compared to K⁺ cation, the c-direction is expanded form 10.275 Å in muscovite to approximately 10.540 Å in tobelite and ND₄-tobelite.  相似文献   

Application of short-wave infrared spectroscopy to define alteration zones associated with the Elura zinc–lead–silver deposit, NSW, Australia     

Yanyan Sun  Philip K. Seccombe  Kai Yang   《Journal of Geochemical Exploration》2001,73(1):63

Short-wave infrared reflectance spectra obtained from a Portable Infrared Mineral Analyser (PIMA) have been used to define alteration zones adjacent to base metal sulfide ore bodies at the Elura Mine, Cobar, Australia. The spectroscopic work identified white mica (sericite), chlorite and carbonates of hydrothermal origin in the alteration zones associated with the ore bodies. Weathering, alteration and ore zones can be discriminated by variations in the intensity and wavelength of relevant absorption features. Hydrothermal alteration is classified into four principal types, namely sericitic, silicic, chloritic and carbonate alteration. The first three types comprise overprinting hydrothermal assemblages of quartz, sericite, chlorite, ankerite, siderite, calcite and sulfides developed in strongly altered metasiltstone and slate of Early Devonian age, adjacent to the zinc–lead–silver mineralisation. An extensive zone of carbonate alteration, manifested as porphyroblasts of siderite in the host metasediments, is recognised beyond the zones of strong alteration. Spectral analysis is consistent with the mineralogical data obtained from XRD and XRF analyses and defines the limits of the alteration zones to distances of about 80 m around the ore bodies. The study demonstrates the potential for spectral analysis to assist with drill hole logging and the identification of alteration zones as part of mineral exploration and development programs.  相似文献   

Remote Sensing Study of Gold Biogeochemical Effects in the Western Guangdong-Hainan Region——A Case Study of the Hetai Gold Deposit     

Xu Ruisong Guangzhou New Technology Institute of Geology  Academia Sinica Jiang Minxi 《《地质学报》英文版》1992,66(4)

The vegetation has been poisoned by gold in the western Guangdong-Hainan region. The gold content ofthe leaves there is as high as 10-1961 times the abundance, the chlorophyll content is 10%-30% lower thanthat of the vegetation in metamorphic terrains and 10%-20% higher than that in granite terrains, and thecarotenoid content is 10%-44% lower than the background value. The water content of leaves is 10% to 20%lower than the background value. The cells of leaves are deformed and broken. The leaf surface shows colourspots and becomes yellow or dark green. The spectral reflectance of the leaf surface is 5%-30% higher than thebackground value: the spectral shape has shifted 5-15 nm to the short wavelength. The gray scales of eanopyon images of Landsat TM and airborne imaging scanner (AIS) are 10%-100% higher than the backgroundvalues. On Landsat TM and AIS false colour images, plants poisoned by gold display a yellow color, whichdisinguishes them from background plants. According to the spectral and image features of goldbiogeochemical effects, the author has constructed a gold information system and expert prediction system,and thus two gold target areas and two gold prospect areas have been identified rapidly, economically andaccurately in the western Guangdong-Hainan region which is extensively covered by vegetation.  相似文献   

Thermal evolution of the Tertiary Shimanto Belt, Muroto Peninsula, Shikoku, Japan     

Michael B.  Underwood  Matthew M.  Laughland  Tim  Byrne  J. P. Hibbard  Lee  DiTullio 《Island Arc》1992,1(1):116-132

Abstract The Shimanto accretionary complex on the Muroto Peninsula of Shikoku comprises two major units of Tertiary strata: the Murotohanto Sub-belt (Eocene-Oligocene) and the Nabae Sub-belt (Oligocene-Miocene). Both sub-belts have been affected by thermal overprints following the peak of accretion-related deformation. Palaeotemperatures for the entire Tertiary section range from ～ 140 to 315°C, based upon mean vitrinite reflectance values of 0.9–5.0%R_m. Values of illite crystallinity index are consistent with conditions of advanced diagenesis and anchimetamorphism. Illite/mica b₀ lattice dimensions indicate that burial pressures were probably no greater than 2.5kbar. In general, levels of thermal maturity are higher for the Murotohanto Sub-belt than for the Nabae Sub-belt. The Eocene-Oligocene strata also display a spatial decrease in thermal maturity from south to north and this pattern probably was caused by regional-scale differential uplift following peak heating. Conversely, the palaeothermal structure within the Nabae Sub-belt is fairly uniform, except for the local effects of mafic intrusions at the tip of Cape Muroto. There is a paleotemperature difference of ～ 90°C across the boundary between the Murotohanto and Nabae Sub-belts (Shiina-Narashi fault), and this contrast is consistent with approximately 1200 m of post-metamorphic vertical offset. Subduction prior to Middle Miocene probably involved the Kula or fused Kula-Pacific plate and the background geothermal gradient during the Eocene-Oligocene phase of accretion was ～ 30–35°C/km. Rapid heating of the Shimanto Belt evidently occurred immediately after a Middle Miocene reorganization of the subduction boundary. Hot oceanic lithosphere from the Shikoku Basin first entered the subduction zone at ～ 15 Ma; this event also coincided with the opening of the Sea of Japan and the rapid clockwise rotation of southwest Japan. The background geothermal gradient at that time was ～ 70°C/km. Whether or not all portions of the inherited (Eocene-Oligocene) palaeothermal structure were overprinted during the Middle Miocene remains controversial.  相似文献