High resolution electron microscopy of tourmaline crystals

Summary High resolution electron micrographs have been obtained from crystals of two types of tourmaline, aligned in a goniometer stage so that the electron beam is parallel to thec axis. Images having a resolution of about 3 Å taken out of focus show direct indications of the atomic arrangement; they suggest medium-range ordering of the metal atoms in buergerite and unexpectedh31l symmetry in elbaite-schorl solid solution. The appearance of ordering is tentatively explained in terms of electron-irradiation effects.

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Hochauflösende Elektronenmikroskopie von Turmalinkristallen

Zusammenfassung Hochauflösende Elektronen-Mikrographien wurden von zwei Typen von Turmalinkristallen, die auf einer Goniometereinrichtung so orientiert waren, daß der Elektronenstrahl parallel zurc-Achse verlief, erhalten. Bilder mit einer 3 Å-Auflösung, die entfokusiert aufgenommen wurden, geben direkte Hinweise auf die Atomanordnung; sie deuten auf Ordnung mittlerer Reichweite der Metallatome in Buergerit und zeigen unerwarteterweiseh31l-Symmetrie bei Elbait-Schörl-Mischkristallen. Das Auftreten von Ordnung wird als vermutlicher Elektronenbestrahlungseffekt gedeutet.

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With 3 Figures     

High resolution aerosol data from MODIS satellite for urban air quality studies

The Moderate Resolution Imaging Spectroradiometer (MODIS) provides daily global coverage, but the 10 km resolution of its aerosol optical depth (AOD) product is not suitable for studying spatial variability of aerosols in urban areas. Recently, a new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm was developed for MODIS which provides AOD at 1 km resolution. Using MAIAC data, the relationship between MAIAC AOD and PM_2.5 as measured by the 27 EPA ground monitoring stations was investigated. These results were also compared to conventional MODIS 10 km AOD retrievals (MOD04) for the same days and locations. The coefficients of determination for MOD04 and for MAIAC are R² =0.45 and 0.50 respectively, suggested that AOD is a reasonably good proxy for PM_2.5 ground concentrations. Finally, we studied the relationship between PM_2.5 and AOD at the intra-urban scale (?10 km) in Boston. The fine resolution results indicated spatial variability in particle concentration at a sub-10 kilometer scale. A local analysis for the Boston area showed that the AOD-PM_2.5 relationship does not depend on relative humidity and air temperatures below ～7 °C. The correlation improves for temperatures above 7–16 °C. We found no dependence on the boundary layer height except when the former was in the range 250–500 m. Finally, we apply a mixed effects model approach to MAIAC aerosol optical depth (AOD) retrievals from MODIS to predict PM_2.5 concentrations within the greater Boston area. With this approach we can control for the inherent day-to-day variability in the AOD-PM_2.5 relationship, which depends on time-varying parameters such as particle optical properties, vertical and diurnal concentration profiles and ground surface reflectance. Our results show that the model-predicted PM_2.5 mass concentrations are highly correlated with the actual observations (out-of-sample R² of 0.86). Therefore, adjustment for the daily variability in the AOD-PM_2.5 relationship provides a means for obtaining spatially-resolved PM_2.5 concentrations.     

High resolution radio refractive index studies in India using airborne microwave refractometers

We discuss high resolution measurements on radio refractive index, in the boundary layer and above the atmosphere in the Indian sub-continent spread over a period of more than a solar cycle by making use of airborne microwave refractometers, operating around 9 GHz. Some atmospheric turbulence parameters comparable with earlier results have also been derived. The results demonstrate sharp gradients of radio refractive index, layer structures and the variability of the boundary layer in time and space. An erratum to this article is available at .     

High resolution radio refractive index studies in India using airborne microwave refractometers

The online version of the original article can be found at     

Surface studies of feldspar dissolution using surface replication combined with electron microscopic and spectroscopic techniques

The replica of a microcline cleavage surface was examined before and at various stages of interaction with water and acid solutions at 70°C. For up to 14 weeks in demineralized water the surface as a whole underwent very little change, except some micrometre-sized particles were found on parts of the surface after only one week. Similar particles were found on the actual cleavage surface and on the surfaces of other microcline powders similarly leached at 22°C. These particles were made up of aluminum and silicon with little or no potassium. They were likely formed in some preexisting activated feldspar lattice, either by solid transformation or by local supersaturation and precipitation from solution.Further leaching for 48 hours in a 0.01 mol·L^?1 solution of hydrochloric acid caused only minor pitting of the same cleavage surface, probably due to enhanced dissolution, while contact with a 0.01 mol · L^?1 solution of hydrofluoric acid caused extensive formation of dissolution pits and channels along crystal defects leading to the removal of large portions of the surface. Neither acid appeared to dissolve the newly formed aluminum silicate particles appreciably.Hence during the incongruent dissolution of a feldspar, most of the reactions, dissolution and formation of authigenic Al-silicate phases, occur preferentially along crystal defects. Since the authigenic phases occur as discrete particles occupying only a small fraction of the parent surface their presence will not affect the bulk composition or the overall dissolution rate of the surface.     

Thermal evolution of organic matter in source rocks — Experimental and scanning electron microscopic studies

Five major forms (lamellar, banded, crack-like, disseminated and segregated encrustation) of organic matter distribution in source rocks have been revealed under scanning electron microscope by using the heavy metal staining technique. The degree of organic impregnation is related to the amount of liquid hydrocarbons in the rocks, and from this relationship a rough estimation of organic matter can be made on the basis of electron microscopic observations. In conjunction with experimental studies it has been found that the distribution forms of organic matter are a function of its maturity in the process of thermal evolution and accordingly some microscopic criteria can be developed for the assessment of source rocks.     

An electron microscopic study of anorthoclase spherulites

Spherulites consisting of fibrous alkali feldspar and silica minerals are produced by devitrification of rhyolite glass under hydrothermal conditions. The alkali feldspars (Ab_72.5Or_23.0An_4.5, Ab_81.7Or_14.0An_4.3) in spherulites from two localities in Japan consist of triclinic anorthoclase showing fine cross-hatched twinning and monoclinic sanidine showing fine cross-hatching not attributable to twinning. The cross-hatching, which corresponds to albite and pericline twinning, is produced in the process of transition from a monoclinic to a triclinic phase. The spherulite may develop at a temperature lower than about 200°C because the co-existing silica mineral is not quartz, but metastable tridymite. According to the phase diagram of the alkali feldspars by MacKenzie (1952), the alkali feldspars should have been triclinic during growth. However, the textures show that the alkali feldspar grew as a disordered monoclinic phase. Because of the high growth rate, the Al/Si disordered structure was produced during growth and afterwards transformed into a triclinic structure with cross-hatched twinning.     

An electron microscopic study of a lunar pyroxene

Ion-thinned samples of lunar rock 12052 have been examined in the electron microscope. Exsolution textures have been observed in the pyroxene on a finer scale than those found in Apollo 11 rocks, indicating a faster cooling rate. The early stages of the reaction involve modulations on both (001) and (100) which suggest that decomposition may occur by a spinodal mechanism. A two-stage exsolution structure in the augite rim of a phenocryst is consistent with a sudden increase in the cooling rate—possibly when the magma was extruded onto the surface of the moon.The presence of antiphase domains in all primary and precipitated pigeonites confirms that pigeonites of all compositions have the space group C2/c at high temperatures.     

High resolution X-ray computed tomography studies of Grasberg porphyry Cu-Au ores,Papua, Indonesia

High-resolution X-ray computed tomography (HRXCT) provides unique information of the geological and metallurgical significance for gold and related ore minerals in the supergiant Grasberg porphyry Cu–Au deposit. Digital radiographs have proved to be an effective means of screening samples for the presence of gold for HRXCT studies. Digital radiograph effectiveness is limited by the thickness of samples (typically to ≤2 cm), as well as the associated minerals. Thus, preselecting samples for gold studies using HRXCT is most effective using digital radiographs combined with assay information. Differentiating between metallic mineral grains with relatively small differences in density, e.g., bornite (5.1 g/cm³) from chalcopyrite (4.2 g/cm³), is relatively straightforward for isolated monominerallic grains or composites in a similar lower-density matrix, but difficulties are encountered with the interpretation of typical intergrown ore minerals. X-ray beam-hardening artifacts lead to inconsistency in attenuation determination, both within and among slice images, complicating quantitative processing. However, differentiation of chalcopyrite and bornite has been successful in smaller-diameter (≤22-mm) cores of Grasberg ores. Small-diameter (≤10 mm) cores of the Grasberg stockwork Cu–Au ore were analyzed using HRXCT methods scanned at the minimum spacing currently available (7.5 μm), and data reduction protocols using the Blob3D program were modified to improve the quantification of grain sizes and shapes. Grains as small as 6.5 μm have been identified. All of these grains are in direct contact with chalcopyrite, providing support for gold distribution in porphyry copper systems being a result of exsolution from copper sulfides. HRXCT scanning (±digital radiography) precisely defines the in situ location of mineral grains of interest within a sample, which then can be studied in conventional petrographic sections, and other types of analytical studies conducted, e.g., gold trace element geochemistry.     

An analytical electron microscopic study of a pyroxene-amphibole intergrowth

Samples of a garnet granulite from the mafic border units of the Lake Chatuge, Georgia alpine peridotite body were found to contain lamellar intergrowths of a pargastic amphibole in augite having the typical appearance of an exsolution feature. Single crystal X-ray diffraction, optical, electron microprobe and conventional and analytical electron microscopic studies have provided data limiting the compositions and structures of the coexisting phases. Individual lamellae of both materials are from 0.5 to 2.0 m in width with the lamellar interface parallel to {0 1 0}. The formulae of the minerals, as determined by a combination of electron microprobe and analytical electron microscopy, are (Na_0.1Ca_1.0Mg_0.6Fe³⁺ _0.3)(Si_1.8Al_0.2)O₆ for the pyroxene and Na_0.7Ca_1.9(Mg_2.1Fe²⁺ _1.4Fe³⁺ _0.5Ti_0.1Cr_0.1Al_0.8)(Si_5.9Al_2.1) O₂₂(OH)₂ for the amphibole. Several other studies have described intergrowths similar to those observed in this work, in general favoring exsolution as the formation mechanism for the intergrowths. In the Lake Chatuge samples however, replacement of pyroxene by amphibole is in part indicated by continuous gradation of amphibole lamellae into amphiboles rimming the clinopyroxenes.Contribution No. 368 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan     

An electron microscopic study of amphibole lamellae in augite

Ion-thinned samples of augite from four plutonic igneous rocks have been examined in the electron microscope at 100 kV. Lamellae less than 0.08 m thick were observed parallel to (010) in all four samples. Electron diffraction shows that the lamellae consist of clino-amphibole, space group I2/m, with crystallographic axes parallel to those of the augite. Analytical electron microscopy of the lamellae in one specimen shows that they are a hornblende. The amphibole lamellae have nucleated at the interface between the augite host and exsolution lamellae of orthopyroxene parallel to (100) of the augite. The interface between the amphibole lamellae and the augite is coherent.It is thought that the amphibole lamellae have formed by exsolution from the augite, implying the existence of finite solid solution between members of the pyroxene and amphibole groups of minerals.     

Investigation of superstructures in mullite by high resolution electron microscopy and electron diffraction

Superstructures in synthetic mullite, Al_4+2x Si_2?2x O_10?x , prepared using the zone melting technique, are studied by high resolution electron microscopy (HREM), electron diffraction, and in situ energy dispersive X-ray spectroscopy. For x=0.40 composition HREM images indicate only short-range order. Near x=0.5 composition mullite has an antiphase domain structure with antiphase boundaries (APB's) oriented parallel to (100). For higher Al-content the APB's run in non-rational orientations which are slightly inclined against the {601}-planes. We propose models for the superstructures in which oxygen vacancies are arranged in channels parallel to the crystal b-axis. The models are supported by a one-to-one match between observed and computer-simulated images. An Al-rich limit of x=2/3 for mullite is deduced on the basis of stereochemical considerations. Different ordering schemes for the tetrahedral cations are believed to result in the orientation change of the APB's near x=0.5 composition.     

中国高分辨率层序地层学研究

高分辨率层序地层学自1995年引人中国以来,经过起步阶段的理论方法探讨和发展阶段的理论研究与应用研究同步发展,目前已进入以应用研究为主的完善成熟阶段.实践证明.高分辨率层序地层学理论方法在中国陆相含油气盆地油气勘探开发中发挥着愈来愈重要的作用,并且研究的领域不断扩展,已经在煤田、砂岩型铀矿等沉积层控矿床的勘探等方面得到广泛应用.然而,高分辨率层序地层学理论还存在许多不足之处,需进一步完善.今后应加强高分辨率层序地层学理论与计算机技术相结合,使其向定量化、模型化方向发展.     

Observation of talc-tremolite interfaces by high resolution electron microscopy

Talc — a sheet silicate and tremolite — a chain silicate are found by electron microscopy and X-ray microanalysis to occur intergrown as bicrystals with sharp, fault-free boundaries in a talc-rich gemstone nephrite from Scortaseo, Puschlav Valley, Swiss Alps. The plane of intergrowth is the (010)-plane for both components. Curving, stepped interfaces are observed more rarely, and these suggest a reaction from tremolite to talc which stopped before completion. The Mg-ions necessary for this reaction may stem from the associated dolomite rock.     

Transmission electron microscopic study of experimentally deformed k-feldspar single crystals

A set of sanidine single crystals were previously deformed at 700° C in a Griggs triaxial press with different crystallographic orientations of the core so as to induce dislocation glide of different slip systems respectively. Deformed crystals have been studied by transmission electron microscopy (TEM) and the activated slip systems have been characterized for two orientations. (010)[001] and (001)1/2[ \(\overline 1 \) 10] systems expected for one orientation (main stress nearly parallel to [012]) are observed, whereas the (001)[100] system expected for the other orientation (main stress nearly parallel to [101]) is never observed. In the latter specimen the deformation is rather difficult and occurs through unexpected systems characterized as (110)1/2[1 \(\overline 1 \) 2] and (1 \(\overline 1 \) 1)1/2[110]. In all the samples studied the deformation is heterogeneous, exhibiting dislocation configurations related to temperature variations.     

Trace elements,crystal defects and high resolution electron microscopy

Intergrowth defects (intercalation of different structure types) are common in some rock-forming minerals and can be demonstrated to affect trace element distributions, especially when new crystallographic site types are introduced by the intercalated structure. Atoms that do not readily substitute into the host crystal may be incorporated within the intercalated structure. Trace element partitioning patterns, EPR data and mineral dislocation densities suggest that dislocations do not exercise primary control on the partitioning of compatible trace elements, but the effects of dislocations on incompatible elements may be important.Intergrowth defects in geologically important materials include disordered intergrowth structures in Sulfides and the stacking and chain-width disorder that is found in pyroxenes and amphiboles from a range of occurrences. Intergrowth defects may range from a few Ångstroms wide to optically resolvable size. It is important to evaluate their effects when interpreting geological trace element data.     

Twin structure in coesite studied by high resolution electron microscopy

A synthetic crystal of coesite, SiO₂, has been found to contain microtwins. The (100) reflection twin has been made evident on incoherent (010) planes. The twin structure is directly imaged by high resolution electron microscopy at 2,5 Å resolution, allowing an atomic model to be proposed. This twin could be incoherent on large surfaces and the dislocation density is predicted. The X-ray crystallographic data are analyzed critically in view of the presence of such defects in single crystals. The mutual orientation between a silicon matrix and coesite precipitates in Czochralski-silicon annealed specimens is proposed to be non unique as a consequence of the easy twinning of coesite.     

High resolution OH observations of Extended Green Objects

Themaser pumping schemes proposed for the various OH lines may not be as clear-cut as they once seemed. The main OH lines, at 1665 and 1667 MHz, are thought to be radiatively pumped, with the radiation typically coming from nearby ultracompact HII regions. Recently, a new class of main-line maser has been posited, collisionally pumped by shocks due to molecular outflows. The W3(OH)/W3(OH)-TW system is the archetype: traditional OH masers are excited by theW3(OH) ultracompact HII region, while collisionally pumped OH masers arise in the younger object W3(OH)-TW, which is driving an outflow. The 1720 MHz OH satellite line maser, typically found in SNR–cloud interaction regions, is thought to be collisionally pumped, as are class I methanol masers found in star formation regions. Thus it is plausible that these two masers arise in similar (shocked gas) circumstances. In this study we observe all four OH transitions in the direction of Extended Green Objects (EGOs) that trace shocked gas (possibly from outflows) in high-mass star formation regions. Previous studies have found a high incidence of class I methanol maser emission in these objects, suggesting that OH(1720) masers might also be abundant in this sample. Observations of 20 northern EGOs (δ > −17°) were carried out with the Jansky Very Large Array of all four ground state OH transitions, the HI line, and the 20 centimeter continuum. Positive detection of OH lines was obtained for 10 EGOs: OH lines at 1665 and 1667 MHz were detected toward 45% of the sample. The stellar OH line at 1612 MHz was detected toward 15% of the sample. The 1720 MHz emission line was detected in only one EGO source, G45.47+0.07, which is also presents the strongest main-line OH emission of our sample. We measure the projected separations between OH masers and GLIMPSE point sources associated with EGOs (median value 0.04 pc), betweenOH and class II methanol masers (median value 0.03 pc), and between OH and class I methanol masers (median value 0.14 pc), thus confirming previous findings that class I methanol masers are located further from exciting sources than areOH and class II methanol masers. Bearing in mind the theoretical incompatibility of class I and class II methanol maser pumping schemes, and the obtained separations between class I methanol masers and other masers in the EGOs, we conclude that class I methanol masers do not co-exist with GLIMPSE point sources, OH and class II methanol masers in one and the same core. Rather, we suggest that the class I masers arise in distinct but neighboring cores, about 1 pc distant, and in a different evolutionary state.

     

高分辨率抛物线拉冬变换多次波压制技术

对于孔径过小,采样不充分的地震数据,抛物线拉冬变换的多次波压制效果不理想,且存在空间假频问题。综合Sacchi、Mauricio、Todd Mojesky等对抛物线拉冬变换压制多次波的分析,阐明了高分辨率抛物线拉冬变换原理。通过理论模型试验和实际地震数据的分析证明,高分辨率抛物线拉冬变换可以突破离散采样和有限孔径的限制,实现对地震数据中的多次波及空间假频的快速、有效压制。