bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of School Culture on Adolescent Behavioural Problems: SelfEsteem, Attachment to Learning, and Peer Approval of Deviance as Mediating Mechanisms
Authors: DeWit David J. , Offord David R. , Sanford Mark , Rye Barbara J. , Shain Martin , Wright Robin
Published: December 2006

Adopting a social ecological perspective, this study examined the role of adolescent personality and social traits as mediating mechanisms linking school culture with adolescent behavioural problems. Data were obtained from the self-reports of 1,100 grade nine students attending four southern Ontario high schools. Structural equation model results revealed that student exposure to an unfavourable school culture (marked by perceptions of low teacher and classmate support, student conflict, unfair school rules and disciplinary practices, and low student autonomy in school decision-making and affairs) was positively associated with low attachment to learning and peer approval of deviance each of which were positively associated with disciplinary problems, conduct disorder, oppositional-defiant disorder, attention-deficit hyperactivity, and substance use. Low self-esteem emerged as a significant mediator in two models. Significant direct effects of school culture were found for most outcomes. Discussion focused on the significance of study findings for future program development and research.
Influence of Family Structure on Children's Self-Concept Development
Authors: Sweeney Rebecca B. , Bracken Bruce A.
Published: December 2006

This research explored the relationships between students' multidimensional selfconcepts as a function of students' family structure. Participants were 815 adolescent and preadolescent children, ages 9 to 19, selected from 17 sites across the four major regions of the United States. Students were classified into five family types (i.e., intact, reconstituted mother-headed, reconstituted father-headed, single parent mother-headed, single parent father-headed). Results indicated that the total self-concepts of students from single-parent families were significantly lower than the global scores of students from intact families. Family self-concepts of students from reconstituted families were significantly lower than students from intact families. This finding highlights the sensitivity of domain-specific selfconcepts.
Testing Competing Structural Models of Approaches to Learning in a Sample of Undergraduate Students: A Confirmatory Factor Analysis
Authors: Donnon Tyrone , Violato Claudio
Published: December 2006

Current research into studying orientations indicate that students are directed by motives and strategies that reflect both surface (reproduction of contextual material) and deep approaches (comprehensive understanding) to learning. Both are influenced by a latent factor emphasizing a students desire to achieve academically. In this study, the application of Biggs' Study Process Questionnaire (SPQ) is used to test competing models of students' approaches to learning in a sample of 504 undergraduate university students at a major Canadian university, 36o junior – 1st year and 2nd,(year (71.4%) and 144 senior – 3rd year and 4th year (28.6%). In addition to an internal consistency and test-retest reliability analysis of the SPQ, a confirmatory factor analysis was utilized to evaluate the goodness-of-fit of three competing models and an alternative structural model of the motives and strategies of students' approaches to learning. The results provided support for a three-factor model of approaches to learning (Comparative Fit Index = .974). The achieving motive and strategy subscales were significant indicators of both surface and deep factors. The internal consistency alpha coefficient was .82, and 3-month test-retest reliabilities for the subscales ranged from .54 to .73. The results support a three-factor model of approaches to learning where surface and deep approaches are accompanied by a third latent factor reflecting student's approach to academic achievement. An understanding of students' approaches to learning enhances the process of learning and teaching by providing practitioners with an insight into the intrinsic and extrinsic motives for learning at school.
Are We Yet Able to Hear the Signal Through the Noise? A Comprehensive Review of Central Auditory Processing Disorders: Issues of Research and Practice
Authors: Levy Simon , Parkin C. Melanie
Published: December 2006

A Central Auditory Processing Disorder (CAPD) exists when a child has apparent difficulty in processing auditory information while possessing normal hearing. CAPD has been implicated by some as the root disorder underlying learning disabilities, Attention Deficit/Hyperactivity Disorder, and Specific Language Impairment. Despite years of research there is little consensus on a definition, criteria for assessment and diagnosis, and the efficacy of remediation and management. This comprehensive review of the CAPD literature examines the prevalence and etiology, assessment methods, differential diagnosis, as wVell as methods of management and remediation. Particular attention is paid to the details of research design and psychometrics. Support for the distinct existence of CAPD would be aided by the development of a modality-specific operational definition, assessment tools that were better standardized and normed, and the use of better control conditions in research.
Beliefs of Sri Lankan Medical Students About Wife Beating
Authors: Haj-Yahia Muhammad M. , de Zoysa Piyanjali
Published: December 2006

The article presents the results of a study on beliefs about wife beating conducted among 476 Sri Lankan medical students. Participants fill out a selfadministered questionnaire, which examines six beliefs about wife beating. Most students tend to justify wife beating, to believe women benefit from wife beating, and to believe the wife bears more responsibility than the husband for violence against her. At the same time, most participants express willingness to help battered women. However, the vast majority oppose divorce as a solution to wife beating and are against punishing violent husbands. The results also reveal that a significant amount of the variance in each of the six beliefs are best explained by the students' patriarchal approach toward women and marriage and by their exposure to violence in their families of origin. The implications of the results for future research and theory development on beliefs about wife beating are discussed.
Predicting the Timing of Women's Departure From Abusive Relationships
Authors: Panchanadeswaran Subadra , McCloskey Laura A.
Published: December 2006

The aim of this study was to investigate forces that affect the timing of women's exit from violent relationships with men. Abused women were recruited from posters in the community and battered women's shelters, interviewed, and followed up for 10 years. Data for this study are based on 100 women and were analyzed using event history analysis. Age, ethnicity, and alcohol consumption levels of both partners predicted the timing of women's termination of abusive relationships. An interaction effect showed that women who scored above the mean on an index of physical aggression and who never used shelter services had the longest trajectories of violence exposure; severely abused women without shelter use were more likely to stay. Our findings indicate that women who receive shelter services endure shorter periods of violence than women who do not access such services. Further outreach, especially to women experiencing high rates of physical aggression, is recommended.
Reconsidering the Relationship Between Alcohol and Lethal Violence
Authors: Phillips Scott , Matusko Jacqueline , Tomasovic Elizabeth
Published: December 2006

Prior event-based research regarding the relationship between alcohol and violence suffers from important limitations, including the absence of a comparison group, an inappropriate comparison group, or a comparison group that could be considered appropriate but does not control for potential confounders. To overcome such limitations, we use a matched pair design. Drawing on interviews with men imprisoned for an aggravated assault or homicide committed in response to a conflict with another man, we examine matched pairs of violent and nonviolent conflicts nested within respondents. The results suggest that guns mediate the relationship between alcohol and lethal male-male violence.
Classifying the Torture Experiences of Refugees Living in the United States
Authors: Hooberman Joshua B. , Rosenfeld Barry , Lhewa Dechen , Rasmussen Andrew , Keller Allen
Published: December 2006

Few research studies have systematically categorized the types of torture experienced around the world. The purpose of this study is to categorize the diverse traumatic events that are defined as torture, and determine how these torture types relate to demographics and symptom presentation. Data for 325 individuals were obtained through a retrospective review of records from the Bellevue/NYU for Survivors of Torture. A factor analysis generated a model with five factors corresponding to witnessing torture of others, torture of family members, physical beating, rape/sexual assault, and deprivation/passive torture. These factors were significantly correlated with a number of demographic variables (sex, education, and region of origin). Post Traumatic Stress Disorder, anxiety, and depression symptoms were significantly correlated with the rape factor but no other factors were uniquely associated with psychological distress. The results offer insight into the nature of torture and differences in responses.
Active Vibration and Noise Control using Smart Foam
Authors: Akl W. , Baz A.
Published: December 2006

A new class of smart foam is developed and attached to a flexible aluminum plate coupled with a rigid acoustic cavity in an attempt to evaluate its effectiveness in controlling the structural acoustics of the plate/cavity system. The proposed foam consists of a passive foam layer bonded to one surface of an active piezoelectric composite whose other surface is bonded to the surface of the vibrating plate. In this manner, the active piezoelectric composite can control from one side the porosity and the acoustic absorption characteristics of the foam and from the other side can suppress the vibration of the flexible plate. With such capabilities, the proposed smart foam can simultaneously control structural and acoustic cavity modes over a broad frequency range.

A finite element model is presented for the behavior of the smart foam when coupled with a plate/cavity system. The predictions of the model are validated experimentally using vibration and/or sound pressure level feedback control strategies. The obtained experimental results are found to be in good agreement with the predictions of the finite element model. Furthermore, it is found that vibration and noise attenuations of about 90% are obtained with control voltages of less than 180 volts for both vibration and sound pressure feedback.
Frequency Response and Jump Avoidance in a Nonlinear Passive Engine Mount
Authors: Jazar G. Nakhaie , Houim R. , Narimani A. , Golnaraghi M. F.
Published: December 2006

This paper explores a model for a nonlinear one-degree of freedom passive vibration isolator system, known as a smart engine mount. Nonlinearities are employed to analyze and possibly improve the behavior of the optimal linear mount. Nonlinear damping and stiffness rates of the isolator have interacting effects on the dynamic behavior of the mount. The frequency response of the system is obtained using the averaging perturbation method, and a parametric analysis shows that the effect of nonlinear stiffness rate on frequency response is opposite to that of the nonlinear damping rate. Stability of the steady state periodic response has also been analyzed. Jump avoidance criteria are introduced, and the conditions for jump avoidance are studied. Closed form solutions for the absolute acceleration and relative displacement frequency responses are derived, since they are essential to use of the RMS optimization method.
Adaptive Focusing Control of DVD Drives in Vehicle Systems
Authors: Pan M.-CH. , Wei W.-T.
Published: December 2006

As DVD players become standard auxiliary parts in vehicles, environmental vibration from harsh driving conditions may cause unacceptable rates of focusing errors. This article presents the implementation of an adaptive servo controller for DVD drives to suppress focusing errors caused by vibrations transmitted through the chassis of a recreational vehicle. This study is divided into two parts: (1) The design and construction of an optical disk drive platform mounted on a vibrating shaker created to imitate a vehicle system in various driving situations, and (2) the realization of adaptive feedforward servo control (AFSC) techniques using the modified variable step-size filtered-x-LMS algorithm (MVSS-FXLMS) in the optical disk drive employed. Experimentation indicates that the feedforward signal generated as an anti-vibration input by the adaptive controller can effectively suppress the focusing errors introduced by the environmental vibration disturbance in vehicle systems.
Construction of Male Sexuality and Gender Roles in Puerto Rican Heterosexual College Students
Authors: Pérez-Jiménez David , Cunningham Ineke , Serrano-García Irma , Ortiz-Torres Blanca
Published: December 2006

In this study, we explored the contextual elements that influence the construction of male gender roles and sexuality among Puerto Rican heterosexual male college students. We conducted three focus groups with students of the University of Puerto Rico. Sessions were transcribed and content analyzed. Participants believed that gender roles are prescribed mainly through mass media and family. The mass media stresses men’s capacity to have frequent sexual relations with multiple partners and take many sexual risks. Men are also socialized to control their emotions and to be dominant.Sexuality is still taboo in the family and church. Safer sex messages are not encouraged and some conceptions of gender roles and sexuality contradict prevention messages. The relevance of these notions for sexuality and men’s health is discussed.
Primary School “Studs”
Authors: Renold Emma
Published: December 2006

Research has yet to fully explore younger boys’ heterosexual cultures beyond an awareness that heterosexual performances are integral to the production of a “real boy.” Drawing upon an ethnographic study of boys’ (and girls’) gender and sexual relations in two contrasting primary schools, this article argues that while most ten- and eleven-year-old boys experience the boyfriend/girlfriend culture as an emotional cocktail of fear and frustration, a minority of boys invest in a privileged hyperheterosexual masculinity as the “studs” of their classes and schools. Detailed case studies illustrate the different ways in which discourses of “heterosexuality” can be drawn upon at this age and offer some insight into the ways in which masculinity, (hetero)sexuality, childhood, and schooling intersect and are negotiated and experienced by preadolescent boys as they make sense of their emerging gender and sexual identities.
Adapting Job Analysis Methodology to Improve Evaluation Practice
Authors: Jenkins Susan M. , Curtin Patrick
Published: December 2006

This article describes how job analysis, a method commonly used in personnel research and organizational psychology, provides a systematic method for documenting program staffing and service delivery that can improve evaluators' knowledge about program operations. Job analysis data can be used to increase evaluators' insight into how staffs administer programs and provide program services, interpretation of outcome data, make comparisons across programs, and assessment of programs' transferability and replication potential. Because of the central role that staffs play in the delivery of client services and client experiences, job analysis has particular promise for evaluating human services and social welfare programs. This article posits that with little added effort, job analysis can be integrated into traditional evaluation activities and the benefits of this addition will be significant. A basic job analysis methodology is described using an example of its application as part of an evaluation of a prisoner reentry program.
Clay minerals formed from micas and chlorites in some New Zealand soils
Authors: Churchman G. J.
Published: December 2006

Clay mineralogical differences between eight soils in South Island, New Zealand, are related to differences in climate, vegetation, and formation time. Alteration of chlorite follows the sequence chlorite→interlayered hydrousmica→chlorite-swelling chlorite→chlorite-vermiculite, with increased weathering leading to the destruction of the chloritic layers. Mica (muscovite) follows two alteration sequences depending on the overlying vegetation. Under tussock grassland the sequence is mica→mica-vermiculite→mica-beidellite→beidellite. This sequence is also followed under beech forest, together with the sequence of mica→vermiculite→beidellite, with pedogenic chlorite forming when the pH is > 4·5. All but one of the interstratified products (the interlayered hydrous mica) appear to be based on a 1:1 regular interlayering of the two components.
The occurrence of palygorskite in Quaternary sediments of the coastal plain of north-west Egypt
Authors: Hassouba H. , Shaw H. F.
Published: December 2006

Sediments from a Quaternary beach ridge complex along the coastal plain of north-west Egypt have been examined by X-ray diffraction and optical and scanning electron microscopy. Palygorskite was identified in the caliche capping the beach ridges and in the gypsiferous marls between the ridges; petrographic evidence indicated that this had formed authigenically in both environments. Examples are thus provided of the pedogenic and evaporative in situ formation of palygorskite.
The transformation of feldspars and muscovite to clay minerals in (Ca,Mg)-carbonate bearing hydrothermal media
Authors: Frank-Kamenetskii V. A. , Kotov N. V. , Rjumin A. A.
Published: December 2006

Experimental transformations of feldspars and muscovites following additions of magnesite and dolomite have been studied at PH2O = 1 kbar, T = 200–600°C. Formation of layer silicates such as smectite, 7 Å (Mg,Al)-serpentine, some mixed-layer phases and other minerals is shown to be a function of the composition of the starting materials, temperature and run duration. It is established that 1 M- and 2 M1-phlogopites are formed from 1 M- and 2 M1-muscovites, respectively, under Mg-bearing hydrothermal conditions. Some causes of variations in the composition of 7 Å (Mg,Al)-serpentines at elevated temperature as a function of the composition of hydrothermal media are given. These data may be used to explain the main characteristics of clay mineral formation from feldspar- and muscovite-bearing sedimentary rocks during their alteration in postdiagenetic and metasomatic processes.
X-ray diffraction from partially disordered layer structures: General case
Authors: Ray B. K. , De A. K. , Bhattacherjee S.
Published: December 2006

A general expression for diffracted intensities from partially ordered layer structures with a ‘mistake’ has been calculated. The ‘mistake’ consists of a shift of a layer parallel to adjacent layers by any arbitrary fraction b/q along the b axis, q being any integer. The expression is free from any simplifying approximations.
Further studies of a ferrous iron doped synthetic kaolin: dosimetry of X-ray induced defects
Authors: Cuttler A. H.
Published: December 2006

The structure of kaolin has been examined together with aspects of dosimetry and energy loss mechanisms of radiation to explain the formation of g = 2 EPR centres. The analysis points to the formation of a trapped hole on the ‘inner layer’ oxygen atoms of kaolin located at the boundaries between divalent ion and trivalent ion ‘cells’, in particular at the boundaries with excess negative charge. Direct interaction of X-rays with atoms and the possibility of proton recoil are eliminated. The means of production appears to be by transfer of charge following ionization of atoms by secondary electrons, with transfer of vacancies ultimately to the oxygen ions. Mechanisms which result in a decrease in signal strength with increase in concentration are examined. It is concluded that the cell mechanisms discussed are consistent with the rates of production and that at 20 Mrad (air) the number of centres should be reaching saturation.
IR spectra of powder hematite: effects of particle size and shape
Authors: Rendon Jose L. , Serna Carlos J.
Published: December 2006

Hematites obtained by heating goethite gave different IR absorption spectra depending on the temperature of formation. Hematites formed between 250–600°C consisted of lath-like crystals (average size 0.4 ×0.08 µm) and showed, in accordance with theoretical predictions, very similar IR spectra whose absorption bands could all be assigned to surface mode vibrations. However, significantly different IR spectra were given by hematites formed between 700–950°C, the differences being correlated with variations in the size and shape of the particles. Differences observed in the IR spectra of powder hematite do not therefore justify new names for the mineral, as have been proposed in the literature.
A method to eliminate the background in X-ray diffraction patterns of oriented clay mineral samples
Authors: Van Der Gaast S. J. , Vaars A. J.
Published: December 2006

A method is described for calculating, and then subtracting, the background from X-ray diffraction patterns of oriented clay mineral samples. Ti-Kα radiation is used and, to minimize the absorption of this radiation by air, a vacuum and helium-flushed device has been developed. This device can be used with other X-ray sources, offering a considerable increase of intensity—e.g. Co-Kα radiation is increased by 125%. With the background-eliminated patterns a better semi-quantitative estimate of the composition of clay mineral mixtures is possible. Small differences in composition of two samples can be identified by subtracting one of the background-eliminated patterns from the other. Using this method, peak maxima of smectite-group minerals can also be accurately determined.
X-ray diffraction of oriented clays in small quantities (0·1 mg)
Authors: Meunier A. , Velde B.
Published: December 2006

Precise identification of clay minerals found in granular rocks has always posed a great problem to the clay petrographer. Even if it is possible to locate the position of authigenic clay mineral formation in a thin section, subsequent identification of this same material by X-ray diffractometry is usually very difficult. Attempts have been made using selected-area radiation of thin sections (Pawluck & Dumanski, 1973; Wicks & Zussman, 1975; Wilson & Clark, 1978) but the area analysed remains relatively large, i.e. of the order of several mm2. The other solution is micro-picking of material from a thin section and subsequent identification by Debye-Scherrer camera methods (Wallace, 1955; Rickwood, 1977). This method, however, does not allow preferred orientation, and thus precise identification, of many clay species. The ideal method is to combine micro-picking from thin sections from areas of several hundreds of square microns with an oriented sample preparation, which can then be treated in the traditional way (glycolation, heating, etc.) for characterization by X-ray diffractometry.
Etude d'une smectite magnesienne de transition, a caracteristiques di et trioctahedriques et derivee de l'evolution superficielle d'une trachydolerite de Provence
Authors: Chevalier Y. , Dejou J.
Published: December 2006

Resume

La phase <2 µm issue de l'évolution géochimique superficielle d'une trachydolérite de Provence s'est révélée être presque exclusivement constituée d'une smectite. Son examen, grâce à plusieurs techniques, et notamment l'identification des produits de recristallisation à haute température, montre qu'il s'agit d'un minéral 2/1, surtout magnésien. L'établissement de sa formule structurale approchée, calculée sur la base de 11 oxygènes, en ferait un minéral intermédiaire entre les smectites diet trioctaédriques, avec une occupation de 2.55 cations en sites octaédriques. Cette smectite de Provence n'est pas une saponite au sens strict, compte-tenu du nombre des cations R3+ = 0.94 en position octaédrique, plus élevé que celui de ces minéraux, tandis que la part des cations R2+ en ces mêmes sites est inférieure au seuil de 85%.
X-ray photoelectron diffraction studies of lepidolite
Authors: Evans S. , Raftery E.
Published: December 2006

X-ray photoelectron diffraction data for three cleavage surfaces from a crystal of a Norwegian lepidolite containing 2·3% Rb and 3% Mn are reported and interpreted. Rubidium is shown to occupy anhydrous interlayer sites equivalent to those of potassium, and to be distributed uniformly throughout the crystals. Cleavage occurs in Mn-rich regions in which the manganese(II) is located in octahedral sites essentially equivalent to those of lithium. The octahedral Al sites can readily be distinguished from the Li,Mn sites and it is concluded that Al occupies predominantly M(2), cis sites while Li and Mn(II) prefer M(1), trans sites. Photoelectron diffraction data also indicate that 40 ± 5% of the Al is tetrahedrally coordinated, compared with a figure of ∼34% deduced independently from a surface analysis.
Le césium, revelateur de structure des smectites
Authors: Besson G. , Glaeser R. , Tchoubar C.
Published: December 2006

Resumé

En utilisant des méthodes diffractométriques avec des smectites mal cristallisées, il n'est pas possible de déterminer de façon précise la répartition des atomes dans le feuillet. Il est particulièrement difficile de confirmer si le mineral est di- ou trioctaédrique, ou de déterminer la position de la vacance (position cis ou trans) dans la couche octaédrique. De même la nature polytypique de ces minéraux est difficile à preciser. La détermination de ces paramètres est difficile car les modulations (hkl) obtenues par diffraction des rayons X avec les smectites sont faibles et très peu marquées. Ce travail montre qu'en utilisant le césium comme cation interfoliaire, il y a non seulement augmentation de l'ordre dans l'empilement des feuillets mais aussi que son grand facteur de diffusion augmente l'intensité des modulations (hkl). En supposant que la substitution par du césium ne modifie pas la répartition des atomes dans le feuillet (il affecte seulement la distorsion de la couche tétraédrique), il est alors possible de déterminer cette répartition.
The in Vitro cytotoxicity of some standard clay mineral dusts in the respirable size range
Authors: Gormley I. P. , Addison J.
Published: December 2006

Seven natural clay minerals (two kaolinites, three montmorillonites, a hectorite and a palygorskite) were tested for their cytotoxicity in vitro using an established cytotoxicity assay. Cellular viability, levels of lactate dehydrogenase, N-acetyl-β-d-glucosaminidase, lactic acid and total cellular protein were measured in cells of the macrophage-like cell line, P388D1, after 48 h incubation with each clay. There was a significant relationship between BET/N2 surface area of the clays and cytotoxicity but in two cases the level of cytotoxicity was apparently influenced by the presence of quartz or cristobalite in the samples. Results are discussed in the light of the available animal and epidemiological data relating to clay minerals.
‘Corrensite-like minerals’ in the Taro and Ceno Valleys, Italy
Authors: Brigatti M. F. , Poppi L.
Published: December 2006

Mineralogical properties (XRD, DTG) and chemical compositions of some chlorite-smectite interlayer minerals in alteration products of ophiolitic rocks from the Northern Apennines are presented and discussed. The presence of iron hydroxides and the continuous variation in Al2O3 content suggest that the corrensites are intermediate stages in the process of alteration of chlorite to smectite in an environment characterized by high element mobility. A thermal test to characterize the swelling component of the interlayer species is proposed.
Interstratified XRD characteristics of physical mixtures of elementary clay particles
Authors: Nadeau P. H. , Tait J. M. , McHardy W. J. , Wilson M. J.
Published: December 2006

Transmission electron microscopic (TEM) examination of the <0·1-µm fraction of montmorillonite and regularly interstratified illite-smectite (I-S) shows that these clays, when dried from suspension, consist primarily of particles 10 Å and 20 Å thick respectively. However, X-ray diffraction (XRD) examination of sedimented aggregates of montmorillonite indicate that the effective number of unit cells that are diffracting coherently is ∼9. This discrepancy can be reconciled by postulating an interparticle diffraction effect from the sedimented aggregates of oriented particles. The interfaces of these particles are capable of adsorbing water, ethylene glycol etc. so that on this basis smectite is composed of elementary silicate particles 10 Å thick, and regularly interstratified I-S is primarily composed of elementary ‘illite’ particles 20 Å thick, values which are in agreement with the TEM observations. This concept is confirmed experimentally by XRD examination of sedimented aggregates from mixed suspensions of both materials; the resulting patterns are identical to those of randomly interstratified illite and smectite layers, which indicates that the layer sequence examined by XRD has been entirely rearranged. It is concluded that the use of XRD peak breadth to determine mean crystal thickness cannot be reliably applied to these systems. Standard XRD data from sedimented aggregates may not be able to distinguish between true interstratification and interparticle diffraction effects of intimate physical mixtures.
The distribution of octahedral cations in the 2:1 layers of dioctahedral smectites studied by oblique-texture electron diffraction
Authors: Tsipursky S. I. , Drits V. A.
Published: December 2006

Olique-texture electron diffraction examination of K-saturated dioctahedral smectites after 70–100 wetting-drying cycles allows the determination of cation distribution betweentransandcisoctahedra of the 2:1 layers. Studies of smectites with different compositions has revealed a wide variety of occupancies of the available octahedral sites.
29Si and 27Al nuclear magnetic resonance spectroscopy of 2:1 clay minerals
Authors: Thompson J. G.
Published: December 2006

Solid-state 29Si and 27Al NMR spectroscopy with magic-angle spinning was used to study two smectites, two illites and a vermiculite. 27Al NMR was able to directly observe the coordination of aluminium. 29Si NMR was sensitive to both the chemical nature of the interlayer species and the presence of aluminium in the tetrahedral sheet. Well-resolved resonances in the vermiculite at δ = −84·6, −88·7 and −92·9 (ppm relative to TMS) were assigned to Q3(2Al), Q3(1Al) and Q3(0Al) respectively. The smectites exhibited single resonances centred at δ = −93 (Q3(0Al)). The illites displayed broad resonances between δ = −80 and −105. The 29Si spectrum of a smectite complexed with alkylammonium cations showed a shielding of up to 1 ppm relative to the untreated sample.
Electron microprobe analysis of clay minerals
Authors: Velde B.
Published: December 2006

The electron microprobe has been used in petrographic research for almost 20 years and more recently as a tool for investigations of clay minerals. However, to the author's knowledge no information has been published concerning the reliability of such analyses―especially those of the alkali elements. Since the alkali contents of clays are often critical, e.g. in determining the smectite content of mixed-layered minerals, it is important to have some idea of the reliability of an analysis made using an electron microprobe.

Three variables can be controlled in electron microprobe analysis—time, beam-current intensity and beam size (the diameter of the beam which excites the sample). Exaggerated conditions of any one of these variables tend to diminish the signal received by the detectors for the alkali elements, especially sodium. As an example, the effect of varying two of these parameters on the intensity of sodium radiation for sodium-aluminumsilicon glass is shown in Fig. 1. The signal decreases (% loss Na) over a 200 s counting time. Beam intensity and beam diameter were varied in this example.
Structure defects in palygorskite
Authors: Lokanatha S. , Bhattacherjee S.
Published: December 2006

It is well established that palygorskite has an amphibole-like, double-chain structure. The linked tetrahedral groups forming continuous sheets are divided into ribbons of various widths due to alternation of the direction of tetrahedra which run parallel to the fibre axis (Brindley, 1980). This alternation of the chains leaves a series of holes of well-defined size which are filled with water molecules (channel water). Based on microscopic observations of cleavage surfaces (Bailey, 1980), the mineral appears to be built up of regular stacking of planes parallel to (h00) and (hk0) which form predominantly the surface of the laths parallel to thec-axis. This is further supported by the enhanced X-ray reflections from these planes. Some degree of structural disorder might be expected to result from the progressive elimination of the channel water on heating. In addition, the weak interchain bonding in palygorskite is likely to result in a shift of the layers parallel to the fibre axis.
Organic reactions as indicators of the burial and temperature histories of sedimentary sequences
Authors: Mackenzie A. S.
Published: December 2006

Three organic reactions which affect individual compounds present in most organic-rich sedimentary rocks have been identified—configurational isomerization and aromatization of steroid hydrocarbons, and configurational isomerization of hopanes. The extents to which these reactions have occurred can be assessed by gas chromatographic-mass spectrometric analysis of the organic extracts of the sediment samples; they provide sensitive indicators of thermal maturation. When combined with the model of sedimentary basin formation by extension of the lithosphere, this molecular approach to the maturation of organic material can be used to constrain the temperature-time histories of sedimentary sequences. This temperature history may be used to integrate the relevant Arrhenius’ and rate equations governing the reaction rates. Each rate equation has three constants—the activation energy, frequency factor and the ratio of forward reaction to backward reaction. These have been estimated using analyses of samples whose temperature-time history is well constrained. The resulting estimates can then be used to reconstruct the temperature-time histories of other samples from organic geochemical data, e.g. calculation of the amount and timing of uplift.
Stability of detrital heavy minerals in Tertiary sandstones from the North Sea Basin
Authors: Morton A. C.
Published: December 2006

Intrastratal solution of detrital heavy minerals in North Sea Tertiary sandstones takes place in two different diagenetic settings, deep burial and acidic weathering. These are characterized by different orders of mineral stability: apatite, chloritoid, garnet, sphene and spinel are less stable in acidic weathering than in deep burial, whereas the reverse is true for andalusite, kyanite and sillimanite. Heavy-mineral dissolution patterns, therefore, do not follow one single order of stability but several, depending on the diagenetic environment in which the dissolution occurs. It seems from this that the relativeorder of stabilityfor detrital heavy minerals is controlled by the chemistry of the interstitial waters, whereas thelimits of persistencedepend on pore-fluid temperature, rate of water throughput, and geological age. Because different diagenetic environments lead to differing orders of mineral stability, it may prove possible to elucidate certain aspects of the diagenetic history of a sandstone by heavy-mineral dissolution patterns.
Quartz diagenesis and convective fluid movement: Beatrice Oilfield, UK North Sea
Authors: Haszeldine R. S. , Samson I. M. , Cornford C.
Published: December 2006

The extent of diagenesis in Lower Jurassic shoreline sandstones of the Beatrice oilfield was controlled primarily by their detrital clay content. Sandstones rich in detrital clay had low depositional permeabilities; these show preservation of detrital feldspars to the present day and have no extensive diagenetic quartz overgrowths. Sandstones poor in detrital clay had high permeabilities and show large quartz overgrowths as part of a normal sub-arkosic diagenetic sequence. Such quartz occurs preferentially below, but not above, impermeable mudstones. These low- and high-permeability features suggest that pore-fluid flow was important during diagenesis. Fluid inclusions trapped in diagenetic quartz overgrowths formed between 68° and 94°C. This silica was probably supplied in solution from the temperature-driven illitization of smectitic clays surrounding these sandstones deeper in the basin. Fluid volumes from clay dewatering, from mechanical compaction, or from influx of overlying seawater were too small to transport diagenetic silica volumes. Silica-rich fluids were probably transported up-dip by convective cells within the sandstones and authigenic quartz precipitated as these fluids cooled. This episode of quartz diagenesis could have been completed within 1·6 × 106 yr if fluid velocities were 3·1 m/yr. Similar convective fluid flows could have transported the fluids responsible for secondary porosity development and the hydrocarbons expelled from mudstones later in the basin burial history.
Volcaniclastics as potential hydrocarbon reservoirs
Authors: Seemann U. , Scherer M.
Published: December 2006

Volcaniclastics have not as yet been considered prime hydrocarbon exploration targets. This is because they contain a high proportion of mechanically and mineralogically unstable components which generally cause a faster deterioration in reservoir quality upon burial than is found in siliciclastics. Also, their complex mineralogical composition makes the burial-related diagenesis more difficult to understand. However, under favourable circumstances—such as devitrification at shallow depth, leaching of unstable particles, fracturing, or reworking—volcaniclastics may act as good reservoir rocks. Both favourable and unfavourable case histories are discussed.
Diffraction effects calculated for structural models of K-saturated montmorillonite containing different types of defects
Authors: Rits V. A. D. , Plançon A. , Sakharov B. A. , Besson G. , Tsipursky S. I. , Tchoubar C.
Published: December 2006

The general approach to the problem of the real structure of smectites requires an analysis based on the relationship between structural characteristics and diffraction patterns. This paper, which considers only the models corresponding to dioctahedral smectites saturated by K-cations and collapsed, includes: 1. Successive consideration of all models which are crystallochemically possible. These models may differ in (i) the structure and chemical composition of layers and interlayer spaces; (ii) the azimuthal orientations, translations and the mode of alternation of the layers; (iii) independent parameters which describe quantitatively the models (e.g. abundance of each type of layer, probability parameters defining the succession of layers, …). 2. Calculation, in all accessible domains of reciprocal space, of the distribution of intensities and profile variations, obtained by changing only one parameter at a time, that defines one type of structural feature (e.g. cation distribution in individual layers, stacking of the layers, nature of stacking faults, …). 3. A systematical analysis of the calculated diffraction patterns to establish the diffraction criteria which will help to interpret the experimental data explicitly.
The rapid formation of crystalline double hydroxy salts and other compounds by controlled hydrolysis
Authors: Taylor R. M.
Published: December 2006

Double-cation hydroxy compounds, generally with the pyroaurite-type structure, were synthesized by a reaction involving the hydrolysis of a cation in solution by a fully hydrolysed and precipitated hydroxide of a second metallic cation. Synthesis of this type of compound is not limited to reactions between di- and trivalent cations as previously thought but can, in this process, involve divalent-divalent, divalent-tetravalent and trivalent-trivalent cations. Crystalline compounds with reasonably sharp XRD patterns formed generally within a few hours at 25°C at pH 4–8·5 depending on the cations involved. The technique presents a more rapid method of formation of these compounds than previously described syntheses, and has been called induced hydrolysis because the fully hydrolysed cation causes complete hydrolysis of the second cation at a pH below that at which this would normally occur. The minerals takovite, Ni6Al2(OH)16CO3·H2O, and hydrotalcite, Mg6Al2(OH)16CO3·H2O, were amongst some of the compounds formed and the reaction is considered to be more realistic in terms of conditions encountered in natural environments than previous syntheses. The reactions described could also be expected to affect the mobility of heavy elements in the environment. These double hydroxy compounds convert on heating between 300–500°C to double-metal oxides with the spinel structure.
Etude par spectrographie infrarouge d'un encroutement calcaire sous galet. Mise en evidence et modelisation experimentale d'une suite minerale evolutive a partir de carbonate de calcium amorphe
Authors: Dupuis T. , Ducloux J. , Butel P. , Nahon D.
Published: December 2006

Resume

Dans les encroûtements calcaires sous galet de la Plaine Poitevine, nous avons mis en évidence, par des méthodes microscopiques, une séquence minéralogique évolutive de la calcite. Par spectrométrie d'absorption infrarouge des éléments de la séquence prélevés en hiver, nous caractérisons, à côté de la calcite (bande à 1420 cm−1), du carbonate amorphe hydraté (bandes à 1405 et 1485 cm−1 et un autre type de calcite (bande à 1445 cm−1). Les résultats d'essais de laboratoire nous permettent d'envisager une évolution du carbonate amorphe vers la calcite par l'intermédiaire d'une phase calcitique transitoire, et d'aragonite toujours en faible proportion. La formation de ces carbonates est liée aux conditions bio-physico-chimiques du sol.
High-gradient magnetic separation (HGMS) in soil clay mineral studies
Authors: Russell J. D. , Birnie A. , Fraser A. R.
Published: December 2006

A modified HGMS system is described in which the inclusion of a peristaltic pump to continuously circulate a suspension of a soil clay through the magnetic trap greatly facilitates the operation of the technique. Application of this purely physical method of mineral separation to a variety of soil clays—using IR spectroscopy to monitor the progress of the separation—illustrates the ease with which magnetic fractions comprising different iron-containing clay minerals may be separated from a single soil clay, thereby making these minerals more accessible for further study by other techniques.
The effect of various clay minerals on the thermal decomposition of stearic acid under ‘bulk Flow’ conditions
Authors: Heller-Kallai L. , Aizenshtat Z. , Miloslavski I.
Published: December 2006

The thermal decomposition of stearic acid in the presence of various clay minerals was studied in an open, inert system under isothermal (250°C) conditions. The distribution of hydrocarbons and the amount of CO2 evolved were determined. The degree of decarboxylation depended on the composition of the octahedral sheets of the clays. It was greater with trioctahedral than with dioctahedral minerals. The presence of dioctahedral minerals tended to reduce the amount of CO2 produced below that obtained with the neat acid. The nature of the hydrocarbons formed depended on the structure of the minerals. Different products were obtained with minerals that have accessible interlayers and channels (smectites, palygorskitesepiolite) than with the 1:1 clays and pyrophyllite or talc. Some minerals caused cracking to light-weight hydrocarbons. Higher surface acidity of the clay interlayers enhanced this process but was not the only decisive factor. In the systems studied, evolution of CO2 did not necessarily precede the formation of light- or medium-weight hydrocarbons from the parent acid.
Mineralogy and origin of Tertiary interbasaltic clays from the Faeroe Islands, Northeastern Atlantic
Authors: Parra M. , Delmont P. , Dumon J. C. , Ferragne A. , Pons J. C.
Published: December 2006

Mineralogical and chemical examination of Tertiary interbasaltic clays from the Faeroe Islands revealed three types of alteration of volcanic tufts and basalts: (1) Argillization of volcanic tuffs within a lacustrine environment resulted in the formation of aluminous beidellites and metahalloysites; these clays are associated with extensive coal layers at Suduroy. (2) Argillization of volcanic tuffs due to hydrothermal action resulted in the formation of thick layers of ferriferous beidellites associated with small amounts of hematite and zeolite (e.g. at Nolsoy). (3) Meteoric alteration of volcanic tufts and basalts, which took place under hot climatic conditions and contrasting seasons, led to the development of ferriferous and aluminous-ferriferous beidellites, metahalloysite, kaolinite, hematite and goethite in low (Høv profile) or high (Øravik profile) topographical positions. The three processes occurred individually or were superimposed.
The influence of aluminium on iron oxides: XIII. Properties of goethites synthesised in 0·3 M KOH at 25°C
Authors: Schulze D. G. , Schwertmann U.
Published: December 2006

Aluminium-substituted goethites were synthesised in 0·3 M KOH at either 25° or 70°C. The 25°C goethites had unit-cell a and c dimensions about 0·1–0·2% larger than the 70°C goethites of comparable Al substitution. Unit-cell b dimensions were similar regardless of synthesis temperature. The 25°C goethites contained larger amounts of Al in their structures than the 70°C goethites synthesised at the same initial Al/(Al + Fe) mole ratio in solution. The 25°C goethites had lower dehydroxylation temperatures and smaller differences between the two OH-bending bands than comparable 70°C goethites. These differences between the two sets of goethites are believed to be caused by the presence of more structural defects in the 25°C goethites than in the 70°C goethites. Goethites with the lowest Al substitutions consisted of crystals with several coherently diffracting domains, while at high Al substitutions the crystals were mainly monodomainic. Surface areas of the 25°C goethites varied in a complex manner as a function of thickness along [100], character of the domains, and physical size.