This article argues that scholars’ current understanding of Social Security policy making in the 1950s is missing a crucial component: massive letter-writing campaigns by ordinary Americans. Americans’ letters to Congress—and the responses of members and their aides in public debates and constituent correspondence—reflect a more vibrant, more democratic, and messier policy-making process than scholars have previously recognized. In the 1950s, Congress voted to amend the Social Security Act of 1935 repeatedly, expanding both the number of occupations covered by the Old Age and Survivors Insurance program and the level of benefits individuals received. Scholars have depicted this expansion as the work of planners within the Social Security bureaucracy. Yet, the letters in congressional records reveal that the process of amending Social Security resulted from—and helped create—constituencies of Americans who felt entitled to make claims on the federal state apparatus.
]]>In the previous two decades, Knowledge Graphs (KGs) have evolved, inspiring developers to build ever-more context-related KGs. Because of this development, Artificial Intelligence (AI) applications can now access open domain-specific information in a format that is both semantically rich and machine comprehensible. In this article, we introduce the XR4DRAMA framework. The KG of the XR4DRAMA framework can represent data for media preparation and disaster management. More specifically, the KG of the XR4DRAMA framework can represent information about: (a) Observations and Events (e.g., data collection of biometric sensors, information in photos and text messages), (b) Spatio-temporal (e.g., highlighted locations and timestamps), (c) Mitigation and response plans in crisis (e.g., first responder teams). In addition, we provide a mechanism that allows Points of Interest (POI) to be created or updated based on videos, photos, and text messages sent by users. For improved disaster management and media coverage of a location, POI serve as markers to journalists and first responders. A task creation mechanism is also provided for the disaster management scenario with the XR4DRAMA framework, which indicates to first responders and citizens what tasks need to be performed in case of an emergency. Finally, the XR4DRAMA framework has a danger zone creation mechanism. Danger zones are regions in a map that are considered as dangerous for citizens and first responders during a disaster management scenario and are annotated by a severity score. The last two mechanisms are based on a Decision Support System (DSS).
]]>Early in World War I, Virginia Woolf wrote these words: ‘The future is dark, which is on the whole, the best thing the future can be […]’. It is tempting to assume that darkness simply hides the unknown and the threatening. It is more challenging to think of it as Woolf did: rich with possibility in even the most desperate times.
We live in what many would readily describe as dark times. These times have brought (among much else) a once-in-a-century public health crisis, the continued redemption of toxic white supremacy, declining trust in and support for public institutions, and growing evidence of impending climate devastation. ‘Dark Futures’ will consider some of the scenes of this devastation and mine them for insights into our predicaments and our prospects.
]]>Relatively strongly stratified turbulent flows tend to self-organise into a ‘layered anisotropic stratified turbulence’ (LAST) regime, characterised by relatively deep and well-mixed density ‘layers’ separated by relatively thin ‘interfaces’ of enhanced density gradient. Understanding the associated mixing dynamics is a central problem in geophysical fluid dynamics. It is challenging to study LAST mixing, as it is associated with Reynolds numbers and Froude numbers ( and being characteristic velocity and length scales, the kinematic viscosity and the buoyancy frequency). Since a sufficiently large dynamic range (largely) unaffected by stratification and viscosity is required, it is also necessary for the buoyancy Reynolds number , where is the (appropriately volume-averaged) turbulent kinetic energy dissipation rate. This requirement is exacerbated for oceanically relevant flows, as the Prandtl number in thermally stratified water (where is the thermal diffusivity), thus leading (potentially) to even finer density field structures. We report here on four forced fully resolved direct numerical simulations of stratified turbulence at various Froude () and Prandtl () numbers forced so that , with resolutions up to . We find that, as increases, emergent ‘interfaces’ become finer and their contribution to bulk mixing characteristics decreases at the expense of the small-scale density structures populating the well-mixed ‘layers’. However, extreme mixing events (as quantified by significantly elevated local destruction rates of buoyancy variance ) are always preferentially found in the (statically stable) interfaces, irrespective of the value of .
The enormous impact of mental illness on work and productivity is a global challenge, with immense costs to wider society. Now is the time for action, with new international guidelines and an emergent consensus on occupational mental healthcare. Alongside governments, organisations and employers, psychiatrists have a leading role to play.
]]>We study numerically the microjetting mode obtained when a fluid is injected through a tube submerged in a uniaxial extensional flow. The steady solution to the full nonlinear Navier–Stokes equations is calculated. We obtain the linear global modes determining the linear stability of the steady solution. For sufficiently large outer viscosity, the flow remains stable for infinitely small values of the injected flow rate. This implies that jets with vanishing diameters can be produced regardless of the jet viscosity and outer flow strength. For a sufficiently small inner-to-outer viscosity ratio, the microjetting instability is associated only with the flow near the entrance of the jet. The tapering meniscus stretches and adopts a slender quasiconical shape. Consequently, the cone tip is exposed to an intense outer flow, which stabilizes the flow in the cone–jet transition region. This work presents the first evidence that fluid jets with arbitrarily small diameters can be stably produced via tip streaming. The results are related to those of a droplet in a uniaxial extensional flow with its equator pinned to an infinitely thin ring. The pinning of the equator drastically affects the droplet stability and breakup.
This introductory Article provides a conceptual umbrella for the Special Issue on Informal Institutions and Democratic Decay. It offers conceptual clarity to studying informal institutions and explains their relationship to other concepts such as constitutional conventions or judicial culture. The article summarizes findings of the Special issue in four key observations. First, it shows that it is impossible to understand the functioning of courts without understanding the informal rules that shape courts’ governance and decision-making. These informal rules (institutions) appear within courts (internal), between courts and other actors (mixed) and among non-judicial actors with effects on courts (external judicial institutions). Second, it identifies a strong trend of formalization of rules, sponsored mostly on the supranational European level .Third, it explains why reforms of formal rules are often not sufficient to trigger behavioral changes and highlights the role of informal institutions in created commitment of actors to key democratic principles. Fourth, it argues that informal judicial institutions significantly impact the quality of democracy.
]]>Women as a social category have been the subject of numerous recent studies considering their lived experience in the Late Antique and Byzantine Mediterranean. However, their representation in the narrative sources continues to shape modern reconstructions of women's agency within their social and economic contexts, often with unsatisfactory results. Building on the twentieth-century sociologist Pierre Bourdieu's model of social capital, this article will use the documentary papyri from Egypt to suggest a paradigm in which the agency of individual women can be viewed and incorporated into micro-historical narratives of the patriarchal society of Late Antiquity.
]]>Let be a smooth affine curve over a number field with a compactification and let be a rank , geometrically irreducible lisse -sheaf on with cyclotomic determinant that extends to an integral model, has Frobenius traces all in some fixed number field , and has bad, infinite reduction at some closed point of . We show that occurs as a summand of the cohomology of a family of abelian varieties over . The argument follows the structure of the proof of a recent theorem of Snowden and Tsimerman, who show that when , then is isomorphic to the cohomology of an elliptic curve .
]]>We present a theoretical analysis of electron pitch-angle scattering by ion-acoustic electrostatic fluctuations present in the Earth's bow shock and, presumably, collisionless shocks in general. We numerically simulate electron interaction with a single wave packet to demonstrate the scattering through phase bunching and phase trapping and quantify electron pitch-angle scattering in dependence on the wave amplitude and wave normal angle to the local magnetic field. The iterative mapping technique is used to model pitch-angle scattering of electrons by a large number of wave packets, which have been reported in the Earth's bow shock. Assuming that successive electron scatterings are not correlated, we revealed that the long-term dynamics of electrons is diffusive. The diffusion coefficient depends on the ratio between the wave packet amplitude and electron energy, . A quasi-linear scaling () is observed for sufficiently small wave amplitudes, , while the diffusion is nonlinear () above this threshold. We show that pitch-angle diffusion of keV electrons in the Earth's bow shock can be nonlinear. The corresponding diffusion coefficient scales with the intensity of the electrostatic fluctuations in a nonlinear fashion, with , while its expected values in the Earth's bow shock are . We speculate that in the Earth's quasi-perpendicular bow shock the stochastic shock drift acceleration mechanism with pitch-angle scattering provided by the electrostatic fluctuations can contribute to the acceleration of thermal electrons up to approximately 1 keV. The potential effects of a finite perpendicular coherence scale of the wave packets on the efficiency of electron scattering are discussed.
]]>Influence of the local-ionization-induced neutral depletion on the thrust imparted by the magnetic nozzle plasma thruster is discussed by simply considering reduction of the neutral density due to the ionization in the thruster model combining the global source model and the one-dimensional magnetic nozzle model. When increasing the rf power, it is shown that the increase rate of the plasma density is reduced, while the electron temperature continues to increase due to a decrease in the neutral density. Since the major components of the thrust are originated from the electron pressures in the source and in the magnetic nozzle, the increase in the electron temperature contributes to the increase in the thrust in addition to the gradual density increase by the rf power. The model qualitatively predicts the reduction of the thruster efficiency by the neutral depletion for the high-power condition, compared with the constant neutral density model.
]]>This article is about J. R. R. Tolkien's adaptation of Pythagorean musical elements in the ‘Song of the Ainur’ of the Silmarillion. It details Tolkien's use of Pythagorean dissonance, along with what that amounts to in terms of musical theory, and explores the epistemological origins of the concept and how it found its way into this work of fiction. On the latter point, Platonism, Neoplatonism, and early Christian theology are considered. This includes the likes of Prudentius, pseudo-Dionysius, Augustine, and Aquinas, among others. The article observes that Tolkien has deliberately chosen a somewhat esoteric element of Pythagorean musical theory, albeit highly relevant to his own historical context, in order to explore concepts of morality along with the traditional, Christian conundrum of predestination vs. free will.
]]>We show that for every finite set of prime numbers , there are at most finitely many singular moduli that are -units. The key new ingredient is that for every prime number , singular moduli are -adically disperse. We prove analogous results for the Weber modular functions, the -invariants and the McKay–Thompson series associated with the elements of the monster group. Finally, we also obtain that a modular function that specializes to infinitely many algebraic units at quadratic imaginary numbers must be a weak modular unit.
]]>When a fluid system is subjected to an acoustic wave (or another periodic actuation), the response of the fluid is not purely periodic, but is rather characterized by the combination of a periodic flow and a steady Stokes drift component, where the former is, in many cases, an acoustic wave and the latter is commonly referred to as acoustic streaming. Classical theories of acoustic streaming have focused on slow acoustic streaming, where the periodic flow is the leading-order flow, and is insensitive to the steady flow component which appears as a small correction and is characterized by a small hydrodynamic Reynolds number. In contrast, Dubrovski et al. (J. Fluid Mech. vol. 975, 2023, A4) tackle the fast acoustic streaming regime – conceived by Zarembo (Acoustic streaming. In High-Intensity Ultrasonic Fields, 1971, pp. 135–199. Springer) approximately fifty years ago – where both the periodic and steady flow components are of a similar order of magnitude such that the periodic flow both supports and is simultaneously impacted by the steady flow. They present a novel theoretical framework that accounts for the convection of momentum both within and between the periodic and steady flow to extend slow-streaming equations to the case of steady flow with arbitrary hydrodynamic Reynolds number. They leverage a scaling analysis of the resulting system of equations and a case study to demonstrate the compatibility of their equations with slow streaming theories and highlight the distinctive features of fast streaming.
We are frequently asking ourselves today about the role of the historian in a rapidly changing world. Some expect the past provide them with an explanation or a justification of the present. Others search in history for the basic roots of identity or even for keys to the future. More than ever we are being faced with what Lucien Febvre perceived to be the social function of the historian: “to organize the past as a function of the present.” From this arises a responsibility toward society, as the knowledge that is being produced gains its authenticity through being stamped as officially “scientific.” Faced with the expectations of society and the attention of the public, the historian has been called upon to disentangle events and to furnish a guiding thread, frequently by blending his role as a critic with a civic and an ethical one. Even when we are not dealing with the attempt to set up the historian, through an appeal to his great expertise, as the licensed sage in town, it must be stressed that assuming the rostrum in response to the questions of the time is-provided that the rules of the discipline are strictly adhered to-perfectly legitimate in that it provides history with signifiant depth.
]]>The effects of reaction time (2 to 72 h) and NH4+/A13+ molar ratio (1.6, 2.4 and 3.2) on the hydrothermal synthesis of ammonium-saponites are investigated. The gels are obtained by mixing powders, resulting in a stoichiometric composition, Mg3Si34Al0.6O10(OH)2, with aqueous ammonium solutions, with and without F, to result in initial NH4+/Al3+ molar ratios of 1.6, 2.4 and 3.2. The solid bulk products are characterized by X-raydiffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) analysis. The cation exchange capacity (CEC) is determined with an ammonia selective electrode and the pH of the water from the first washing is measured. Ammonium-saponite is formed rapidly within 16 h. A higher NH4+/A13+ molar ratio and the presence of F facilitate the crystallization of saponite. Small metastable amounts of bayerite, Al(OH)3, are present at low NH4+/A13+ molar ratios; after short reaction times, they disappear. During the first 4 h, the pH decreases rapidly, then drops slowly to a constant level of approximately 4.6 after 60 h. With increasing reaction time, saponite crystallites grow in the ab directions of the individual sheets with almost no stacking to thicker flakes. The NH4+ CEC of the solid products increases strongly within the first 24 h. A maximum of 53.3 meq/100 g is observed. The saponite yield increases from approximately 25% after 2 h to almost 100% after 72 h.
]]>It is said that all philosophy is nothing other than a commentary on Plato.
Maybe.
But was not Plato himself a commentary on Parmenides, Heraclitus, the Pythagoreans, and the Sophists, not to mention Socrates?
And conversely, too, the Commentary on Aristotle composed by St Thomas was not the personal philosophy of Thomas Aquinas? Or then again, do Proclus’ Commentarii in primum Euclidis Elementorum librum not embody a new and original neoplatonic philosophy of mathematics?
]]>What is true of the natural and biological heritage is also the case with cultural diversity: efforts to conserve national languages, rites and traditions are swept along by the rising tide of globalization. But at the same time fashions come and go, buildings rise out of the ground, theories are constructed, new techniques result in hitherto unknown lifestyles. The cultural patchwork is like a shifting kaleidoscope. Of course this does not prevent losses from seeming to accelerate more rapidly than new creations, so that laws have become necessary to put a brake on these destructive developments.
]]>Rectorites containing various amounts of Ca were found at the Sano Mine, Nagano Prefecture, Japan. The Ca content in nonexchangeable form varied from 1.0 to 3.9% CaO. With more than 3.4%, they may be called Ca-rectorite. Chemical data of the most Ca-rich sample showed that Ca was the dominant interlayer cation, and gave a structural formula of (Mg0.16)EX(Ca0.59Na0.27K0.17)FIX[Al3.94Mg0.08 Fe0.07Ti0.01](Si5.85Al2.15)O20(OH)4. This sample is apparently the most Ca-rich rectorite reported to date. The Greene-Kelly test and an intercalation examination by octadecylammonium indicated that the expandable component layers were beidellitic. Assuming the tetrahedral composition of the expandable component layers are similar to the average tetrahedral composition of beidellite of (Si3.6Al0.4), the tetrahedral composition of the mica-like component layers was calculated to be (Si2.25Al1.75). This was closer to a brittle mica (margarite) than to a true mica. Examination of chemical data for several Ca-rectorite samples from different localities, including those from the Sano Mine, showed a trend of increasing Ca content as Al increased and Si decreased. Ca-rectorite exhibited characteristic infrared absorption bands at 480, 670–700 and 900–930 cm−1, which became more intense as Ca content increased. These bands also corresponded to major absorption bands of margarite.
]]>After several recent special issues, conceived and prepared successively by R. H. Robbins and E. M. Uhlenbeck (no. 153, ‘The Cultural Heritage: Languages in Peril”), Y. M. Coppens (no. 155, “From the Heavens to the Mind”), M. Matarasso (no. 158, “Shamans and Shamanism: On the Threshold of a New Millennium”), Diogenes turned to Julio Labastida, coordinator of the study of the social sciences at the National University of Mexico and contributing editor to Diogenes (he is in charge of the Spanish edition), and asked him to gather together for the current issue a certain number of articles devoted to themes related to the five-hundredth anniversary of America's “discovery” and its entry into a unified world.
]]>Unesco's first Philosophical Encounters were held last year at Paris on the theme of “What Do We Not Know?” and they were a great success. Diogenes published some of the papers by participants in its No. 169. A second meeting was held from March 27-30, 1996, devoted to a question as simple and difficult as that of the first: “Who Are We?” Once again this journal will not be able to publish all contributions, but is fortunate enough to present at least some of them to its readers.
]]>This is a transcription of Jean d'Ormesson's speech at UNESCO at the 50th anniversary celebrations of Diogenes in 2003. He describes the journal's origins, inspirations and editors, and the unique place it occupies in the promotion of international, interdisciplinary scholarship.
]]>The slave route from Africa to the Americas is as old as the contact between Europe and the New World itself, and the slave route across the Sahara is older still. Hence to describe the lives of ordinary people in western Africa during the era of slavery would require an examination of the whole of African history over the past five hundred years and more. And in Africa, as in Europe and the Americas, there was tremendous change over this period and extensive variation at any point in time. Life in 1807, when Britain and the United States outlawed the slave trade, was considerably different than in 1492, when Columbus first sailed to the Caribbean. Hence to give an impression of how people in Africa lived during the era of transatlantic slavery is also to understand how the lives of people changed over the course of the slave trade. In 1492, a coup d’état brought a Muslim ruler, Askia Muhammad, to the throne of the great empire of Songhay, and for the next hundred years, Songhay ruled much of West Africa. As empires have always done, Songhay's influence extended to areas beyond its military control. At this time, the slavery of Africans in the Americas was in its infancy. Yet, in 1593, a military invasion from Morocco across the Sahara destroyed Songhay, and much of the internal cohesion of western Africa came to an end, precisely when transatlantic slavery emerged as the principal means of exploiting the agricultural and mineral wealth of the Americas. The lives of ordinary people changed because of this monumental collapse of Songhay. Similarly, the changes imposed by European abolition of the slave trade after 1807, although confusing and often delayed in their impact, were also monumental. Hence the first task in considering how people lived during the slavery era is to identify the differences over time that affected both people who were forced, through slavery, to cross the Atlantic and those who remained behind in Africa. Africa in 1492 or 1593 was not the same as in 1807, any more than Europe and America were.
]]>As a consequence of treatments with glycine solutions, glycine molecules enter the interlayer of both Ca- and Cd-rich montmorillonite. Measurements of d value suggest that at low glycine concentration (0.01 and 0.1 M glycine solutions) a “flat” arrangement of the glycine molecules occurs in the interlayer. In contrast, intercalation of more than one monolayer of glycine molecules occurs for the montmorillonite treated with a higher concentration of glycine (1 M glycine solution).
Interlayer complexation of glycine occurs only for the Cd-rich form of montmorillonite, whereas no complexation is observed for Ca-rich montmorillonite. Both nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) results suggest that the adsorbed glycine, which fully protonates in the interlayer of montmorillonite to give the GlyH2− species, interacts with the interlayer Cd2+ to form the CdGlyx complex mainly through the carboxylate group. The interlayer cadmium, present as both Cd2+ and CdCl−, is complexed by the ligand glycine. In contrast, the cadmium adsorbed on the external surfaces of montmorillonite does not interact with the ligand. Complexation of CdCl+ only occurs for large amounts of adsorption of glycine (e.g., for samples treated with 1 M glycine solution).
]]>Clay mineralogy and whole-rock chemistry of the borate-bearing layers of the Hisarcik and Esbey mines were examined. The Hisarcik clays occur as laminated or unlaminated clay layers with sharp contacts. Unlaminated layers contain quartz derived from metamorphic rocks and carbonate fragments in a clay matrix, and are interpreted as reworked tuffs deposited in playa-lake environments. An important feature is that the unlaminated clays contain little MgO (3–15 wt. %) as compared with the laminated clays (15–30 wt. %). As previous studies have shown, the clay fraction of the studied profile contains predominantly Li-bearing saponite, and accounts for 60–90 wt. % of the clay fraction (<2 μm). Illite in the clay fraction varies from 0 to 67 wt. % and the average illite percentage never exceeds 40 wt. %. Chlorite is scarce (2–5 wt. %). Illite-smectite interstratified clays (illite at 70%, smectite at 30%) were only found in low concentrations in the laminated clay layers of the upper limestone unit (above the borate zone), where illite-2M of detrital origin is also present. The Esbey clays occur interstratified with colemanite layers and envelope colemanite nodules. Calcite is the major mineral of the clays whereas quartz, plagioclase, feldspar, colemanite, and cahnite are minor components. The MgO contents vary between 4.70–13.95 wt. % in the clays interstratified with colemanite layers, between 7.24–11.89 wt. % in the enveloping clays, and between 10.27–21.25 wt. % in clays located above the colemanite zone. The composition of the clay fraction (<2 μm) in all samples is similar. Smectite represents between 40–90 wt. % of the clay fraction in the upper portion of the stratigraphic profile and decreases towards the lower part of the stratigraphic profile. Smectite always occurs with illite which may vary from 20 to 90 wt. % of the clay fraction, and a small amount of kaolinite and chlorite. Illite-2M polytype is abundant. The d(060)-reflection position suggests that the smectite minerals from the Hisarcik and Esbey colemanite mines contain both dioctahedral and trioctahedral smectites to form a transitional zone. These smectites are a product of a magnesium-rich alkaline playa-lake environment.
]]>Six kaolin samples from the Lower Tertiary Huber Formation near Wrens, Georgia were analyzed using transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), chemical analysis, and magnetic susceptibility to characterize the Ti-bearing phases. Selected samples were treated with 5 M NaOH to remove kaolinite and concentrate the Ti-bearing phases for additional analysis. TiO2 content in the bulk fraction ranges from 1.2 to 5.4 wt. %. There are at least three Ti-bearing phases, including anatase, rutile, and a poorly defined nanocrystalline form. Anatase is most abundant and is commonly found with {010} faces in association with kaolinite edge and basal faces. The nanocrystalline form occurs at 0–1 wt. %, and rutile occurs in trace amounts. Bulk XRD analysis correlates well with the bulk TiO2 chemical measurements. Average anatase unit-cell parameters are a = 0.37908 ± 0.0002 nm and c = 0.951 ± 0.001 nm. These parameters indicate an approximate chemical formula of Fe3+0.05Ti4+0.95O1.95(OH)0.05.
The distribution of TiO2 content as a function of depth may be useful to obtain original grain-size variations associated with relative sea-level changes responsible for the deposition of the Huber Formation. Evidence for original depositional sediment properties can be seen in the occurrence of pseudomorphic replacement of micas and fecal pellets by kaolinite. Additional evidence for post-depositional changes includes the sub-micrometer euhedral character and low Fe content of the anatase (relative to soil-derived anatase). These observations for the Huber Formation are consistent with a previously published theory for kaolin genesis that includes biomineralization of originally coarser-grained aluminosilicates into a kaolinite-rich ore body.
]]>The highest frequency near-infrared (NIR) combination bands for specimens of four species of mica—montmorillonite-beidellite, illite, chlorite, and kaolinite—were correlated with respect to Al2O3 content. A direct linear correlation was found between the combination band positions and the Al2O3 contents of the montmorillonite-beidellite series, which may be given as: ν̄ cm−1 = (5.38 ± 0.04) (% Al2O3) + (4412.8 ± 0.9). A similar linear correlation for muscovite is: ν̄ cm−1 = (6.10 ± 0.25) (% Al2O3) + (4434.1 ± 8.3).
Possible NIR band interferences are shown for different mineral mixtures, along with the correlation of different illites with muscovite. No combination bands were found in the frequency region 4425 cm−1 to 4625 cm−1 for specimens in which the Al2O3 content was only in the tetrahedral layer sites.
]]>Redox properties of iron-bearing mineral surfaces may play an important role in controlling the transport and transformation of pollutants into ground waters. Suspensions of seven iron-bearing minerals were reacted with pH and redox indicators under anaerobic conditions at the pH of the natural suspension. The responses of the indicators to the mineral surfaces were monitored by UV-visible spectroscopy using a scattered transmission technique. The Hammett surface acidity function (Hs) and the surface redox potential (Ehs) of these iron-bearing minerals were measured. These measured values were used to calculate Eh values for the seven minerals: goethite = +293 mV; chlorite = +290 mV; hematite = +290 mV; almandite = +282 mV; ferruginous smectite = +275 mV; pyrite = +235 mV; and Na-vermiculite = +223 mV. Calculated surface redox potentials of minerals are different from their potentials measured by platinum electrode in bulk suspensions. UV-visible spectroscopy provides a quick and non-destructive way of monitoring organic probe response at the mineral surface.
]]>In this paper atomic force microscopy-studies are reported suggesting the existence of vicinal faces on the (100) plane of artificially grown goethite. Goethite crystals are commonly regarded to have boundary planes of (100), (010) and (001) faces. In contradiction to these theoretical models TEM and SEM images exhibit (110) and (021) faces to be dominating. These goethite particles consist of many crystallographic coherent domains so that the existence of dislocations on the surfaces has to be assumed. These sites on the surfaces may serve as a nucleation site for the formation of steps. The vicinal faces on the (100) face found with the AFM are (021) faces. They influence the growth velocity of the (100) face to such a degree, that this face vanishes and only (110) faces remain as stable boundary surfaces. The (021) faces are also stable, but have the highest growth rate among the faces considered.
]]>The Source Clays Program of The Clay Minerals Society was initiated in 1972 to distribute a set of reference clays, so that distributed clays could be identical for all recipients. Because most clays do not consist of a single phase, the immediate objective was not to produce a pure product consisting of one clay mineral, but to provide a uniform product. These materials were collected and processed carefully, and sufficient amounts were collected so that material was available for researchers for many years, Large numbers of researchers were thereby assured of working on identical material. Initial descriptions of these materials were presented in the Data Handbook (van Olphen and Fripiat, 1979). An updated version of this book was suggested several years ago because of the availability of new analytical techniques and to provide descriptions of material added to the reference set since 1979.
]]>Eric Hobsbawm is a man of the Enlightenment: does he not define socialism as the last and most extreme heir of the eighteenth century's rationalism? So it is not surprising that the distinction between ‘modern’ and ‘primitive’ or ‘archaic’ has an important place in his work. However, examining some of his writings, and in particular the three books from the period 1959-69 devoted to so-called archaic forms of revolt, it is evident that his approach differs markedly from the ‘progressive’ orthodoxy in its interest, sympathy, even fascination - these are his own words - for ‘primitive’ movements of peasant antimodern (anti-capitalist) resistance and protest. I refer to Primitive Rebels (1959), Bandits (1969) and Captain Swing (1969).
]]>Which traveler, passing through the rural communities of Asia, has not been intrigued by the existence, on the periphery of the village, of shrines, piles of stones, trees, or caverns ornamented with offerings which, at certain key moments during the year, become the focal points of an intense religious activity? These sites are in fact consecrated to chthonian forces that, next to the ancestors, occupy a high rank in the relationship that the peasants of Asia or other regions around the world establish with the divine. To be sure, the earth gods and the ancestors do not put themselves at the top of the pantheon that each society neatly builds for itself; but they nevertheless dominate the immediate sphere of individuals and social groups. They are at the center of their most routine cultic activities, and they are bestowed with a crucial role in the perpetuation of the groups with which they are identified and whose unity they symbolize.
]]>A riddle or a joke? I regret having made light of both myself and the reader. However, the concept of complexity has been explored with such intensity and pedantry, has been analyzed from so many points of view – the mathematical, linguistic, physical, chemical, political, psychological, sociological, physiological, algorithmic, logical, religious, and metaphysical – that nothing, not even the title of this piece, can escape it. Indeed the situation has reached the point where we grow misty-eyed over the very thought of the discrete charms of yesterday's simplicity. Sometimes we dream that complexity itself, after having given us so much, muses – now that its task is fulfilled – of flying up miraculously into the sky, like the Virgin Mother (the Assumption); or ourselves wish to experience – for those spirits who prefer to keep their feet on the ground(!) – the “dissolution” with which entropy begins. Isn't it true that certain words, marked by the spirit of their age, are themselves in fact carried away by the spirit of the age?
]]>On November 9, 2002, a few hundred people, mostly mental health clinicians, gathered at the New York University Medical Center for two days of discussions on the theme, September 11th: Psychoanalytic Reflections in the Second Year. The conference was sponsored by the five New York Societies of the International Psychoanalytical Association. The presentations described various bits of learning that seemed to be emerging from the crisis clinical work with so many traumatized people since the attack on the World Trade Center. This paper discusses three of those presentations in the context of the author's reflections based on his psychotherapeutic work with very troubled patients in a therapeutic community setting. He emphasizes the effect of trauma, not only on individuals, but on the holding environments and symbolic order on which human beings depend for their psychic survival.
]]>Three authigenic muscovite morphologies are associated with Norphlet Formation stylolitization observed in the Texaco Mobile Area Block 872 #1 well: l)large crystals of 1M muscovite, which grew in the stylolites with their c-axes parallel to the plane of maximum compressive stress; 2) fine-grained bundles of muscovite that occur as pore-fillings near stylolites; and 3) pods of fine-grained muscovite that exist within stylolite insoluble residue and that were precipitated as pore-filling muscovite before the host sandstone pressolved.
The population of large crystals of 1M muscovite grew at 51 ± 9 Ma, pore-filling muscovites precipitated at 77 ± 22 Ma, and muscovite pods have ages of 86 ± 16 Ma, as indicated by 40Ar/39Ar laser fusion. Apparent ages indicate that stylolitization was coincident with the beginning of organic maturation Zone 5 and could be the product of reservoir fluid pressure fluctuations induced by gas leakage. The lower Smackover Formation source/seal rock, acting as a pressure relief valve, could have been compromised by microfractures occurring during hydrocarbon generation and expulsion. Decreases in reservoir fluid pressure would have acted upon the sandstone framework by increasing the effective overburden pressure, thus making the rock more susceptible to pressure solution.
Stylolite frequency and quartz cement volume increase in the finer grained portion of the conventional core. Quartz cement volume correlates inversely to percent sandstone porosity. Apparent muscovite ages indicate that stylolitization occurred after hydrocarbon migration. Silica mobility was limited because pressure solution mineral products were precipitated from within grain films of irreducible water within the sandstone.
Stylolitization of quartz grains accounts for a minimum of 34% of the quartz cement in the upper cored section of the Norphlet Formation and minimum of 17% of the quartz cement in the lower cored Norphlet Formation. Quartz cement volumes are based on stylolite insoluble residue thickness and weight measurements of pyrobitumen within and nearby the insoluble residue seams. Stylolitization of K-feldspar and precipitation of muscovite can release additional silica which may have precipitated as quartz cement.
]]>The overuse of water resources in the upper reaches of the Tarim (Xinjiang, China) jeopardizes the ecosystem of the huyang (Populus diversifolia) in the middle reaches of the river, which has led the authorities to displace the population of Caohu (Luntai-xian) in the name of environmental security. This paper discusses the ethical basis of such operations by comparing different approaches, and concludes that establishing a genuine environmental ethics implies an ontological revolution: one that will replace the ‘being towards death’ (Sein zum Tode) of the modern ontological topos of ‘individual body: individual person’, with the ‘being towards life’ (sei e no sonzai) of what Watsuji defined as ‘the structural moment of human existence’, in which being cannot be dissociated from context and history. This ontological revolution, which links human subjecthood with the environment itself, is by the same token the condition of sustainability, which is the most basic human security of all.
]]>Lower Wham Brake is a cypress, rim-swamp artificially enclosed in 1950 as a 22 km2 industrial reservoir by the International Paper Company (IPC)-Bastrop Mill, for regulating downstream water quality. Sediment cores were examined by XRD to differentiate paper-mill effluent deposition from the underlying detrital sediments and by 210Pb decay spectroscopy to determine sediment accretion rates.
Anatase and kaolin from the IPC paper-mill effluent delineated a well-defined, anthropic, silty-clay, A horizon above a clay, 2Ag horizon. Anatase concentrations were no greater than 1.7% in the A horizon and was absent in the underlying 2Agl horizon. Kaolin deposition was significantly correlated to the A horizon by an average increase of 84% above the kaolinite detrital background. Pyrite was detected in the A horizon as a transformation mineral following sulfur reduction of the paper-mill effluent.
Five of the six sediment cores showed an inflection in the excess 210Pb activity profile consistent with a present-day reduction in sediment supply. The average modern sedimentation rate was 0.05 cm yr−1. Average sedimentation observed during historic accretion was 0.22 cm yr−1, about 4.4 times greater than the modern rate of accretion. Reduction in sediment accretion can be attributed to upstream levees completed in 1934 and loss of organic accumulation following the 1950 reservoir impoundment. However, radiometric dating could not precisely correlate the geochronology of kaolin/anatase introduction due to complex oxidation/reduction cycles concurrent with the modern accretion regime.
]]>Forty years ago, Roger Caillois approached the International Council for Philosophy and Humanistic Sciences and proposed that the Council establish a most unusual journal. At the request of UNESCO, the council had brought together a number of learned organizations in the realm of the humanities; Jacques Rueff had just assumed the presidency. In Caillois's mind, the objective was to put an end to the isolation enjoyed by most disciplines, which jealously guarded their prestige and authority and cared little to have their neighbors meddle in their affairs. For Caillois, the musicologist needed the classicist, the prehistorian the philosopher and, of course, the religious historian the linguist and the economist. The interdisciplinarian, at that time, attracted a fair amount of attention. But Caillois was not satisfied. Too often, it seemed to him, the interdisciplinarian was content with arbitrary and superficial juxtapositions. Caillois wanted to raise the transdisciplinary to the level of a methodology, and he wanted to try to draw together the different scholarly sectors reluctant to step beyond historical boundaries all too often frozen by time. Haunted by the theme of the chess board at least as much as by the medusa or by fulgora lantern flies, he coined a term of his own for all this, a term destined to a brilliant future: the lateral sciences.
]]>Scholars from different disciplines are seeking to construct the new field of post-communism, which has been created by the implosion of the communist regime. They explore the most important dimensions of the differences between various types of space and geographical territories: the spaces of identity and the social, political and geopolitical spaces in certain countries of Central Europe (Poland, Hungary, the Czech Republic, Slovakia), the Balkans (Albania, Bosnia, Bulgaria, Macedonia, Romania, Serbia) and the Russian world and its Eurasian borders (Russia, Mongolia, Buriatia, Kazakhstan, Moldavia and the Baltic states) not to mention the borders of the Middle or Far Eastern communist world (descriptions of China and the Middle East).
]]>A new appraisal of radiation-induced defects (RID) in natural kaolinite, i.e., positive trapped holes on oxygen atoms, has been undertaken using Q-band EPR spectra, recorded at 93 K, of irradiated annealed and oriented kaolinite samples originating from various environments. Three different centers were identified. Two of the centers, A- and A’-centers, are trapped holes on oxygen from Si-O bonds. They have a distinct signature and orthogonal orientation, i.e., perpendicular and parallel to the (ab) plane, respectively. The third center, the B-center, is a hole trapped on the oxygen bonding Al in adjacent octahedral positions (AlVI-O−-AlVI bridge). This confirmed some previous assignments from the literature, some others are no longer considered as valid.
A least squares fitting procedure is proposed to assess the RID concentration in any kaolinite. It allows a quantitative approach of the thermal stability of RID. Isochronal annealing shows that the thermal stability of the centers decreases in the order A, A′, B over the temperature range 0–450°C: (1) B-center is completely annealed above 300°C; (2) A′-center can be annealed by heating at 400°C for more than two hours; (3) A-center is stable up to 450°C. The activation energy and the magnitude of the mean half-life for A-center is evaluated through isothermal annealing at 350, 375 and 400°C, with Ea = 2.0 eV ± 0.2, and t½ > 1012 years at 300 K. The stability of A-center seems to decrease with increasing crystalline disorder. Nevertheless, it is high enough for radiation dosimetry using kaolinites from any environment on the Earth's surface.
]]>Intercalation of naphthalene and anthracene into alkyltrimethylammonium (CnH2n+1(CH3)3N+; n = 8, 12, 14, 16, and 18)-montmorillonites was carried out by novel solid-solid reactions at room temperature. Octyltrimethylammonium(C8)-montmorillonite did not form an intercalation compound with either naphthalene or anthracene. Naphthalene was intercalated into both dodecyltrimethylammonium(C12)- and octadecyltrimethylammonium(C18)-montmorillonites to give intercalation compounds. On the other hand, the solid-solid reaction between dodecyltrimethylammonium(C12)- or tetradecyltrimethylammonium(C14)-montmorillonite and anthracene gave only partly intercalated compounds while hexadecyltrimethylammonium(C16)- and octadecyltrimethylammonium(C18)-montmorillonites gave single phase intercalation compounds. The hydrophobic interactions between alkylammonium-montmorillonites and the aromatic compounds are thought to be the driving force for the solid-state intercalation. The extent of the increase in the basal spacing may also be involved in the different reactivity.
]]>Analytical electron microscopy was used to confirm the location of pillars of zirconia in pillared montmorillonite. Data show that the pillared clay is of “high” quality, with surface areas ranging from 200 to 250 m2/g and (001) spacings in the 17–18 Å range. The zirconia-rich pillars were observed using bright-field imaging, annular dark-field imaging, and energy-filtered imaging. The composition of the pillars was confirmed by performing nano-analysis using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. The pillars apparently have an irregular shape <50 Å in size. The shape and relatively large size of the pillars suggest that zirconia dispersion is not ideally distributed in this sample. This study is apparently the first report of electron microscopy observation of pillaring material in clays.
]]>The thermodynamic cationic exchange process involving divalent (Cu, Zn, Cd, Hg, Pb and Ca) and monovalent (Na) cations in Brazilian red Latosol soil was studied. Using a batchwise method, the exchange was monitored as a function of the added cation concentration and the aqueous suspension of the soil at different temperatures. The isotherm series obtained were adjusted to a modified Langmuir equation, whose results were compared with the proposed Rawat method. The cationic exchange equilibria constants (ln K) vary from 1.97 to 9.80 for the Langmuir equation and 7.06 to 13.50 for the Rawat method. The variation in enthalpies obtained by applying the van't Hoff equation gave, for Langmuir and Rawat procedures, exothermic values for Cu (65.5 and 97.3), Cd (36.9 and 45.6) and Pb (43.0 and 50.7) kJ mol−1, and endothermic values for Zn (40.8 and 30.5), Hg (15.0 and 11.3), Ca (30.4 and 40.0) and Na (32.7 and 42.3) kJ moL−1. The exchanges proceed spontaneously, as indicated by the free energy values: Cu (14.2 and 27.2), Zn (21.6 and 32.0), Cd (16.1 and 23.2), Hg (13.8 and 22.9), Pb (22.6 and 28.3), Ca (17.0 and 25.9) and Na (9.9 and 19.3) kJ mol−1 at 323 K. These results suggest that the interaction occurs by complex formation between the organic matter of the soil matrix and the cations dispersed in aqueous solution.
]]>The relative growth rates of the three joint chains of silica tetrahedra and metal octahedra in the [100], [1̅10] and [1̅1̅0] directions within the mica layer (referring to the 1M unit-cell) seem to control the morphology of mica crystallites. Laths and fibers are the products of relatively fast growth along the [100] direction compared to growth along the [1̅10] and [1̅1̅0] directions. The (010) growth front in 1M micas with trans-octahedral vacancies exposes a pair of reactive OH ions that can form organic or inorganic complexes and ‘poison’ the growth on the (010) face.
Authigenic illite fibers in two sandstones with contrasting lithologies are found to have grown on mica or kaolinite cores. Illite fibers appear in single sets or in multiple sets, 120° apart. This texture seems to be related to the stacking sequence of the layers in mica or kaolinite in the core of these fibers.
]]>In general, the N2-BET surface areas of sepiolite samples range from 95 to 400 m2/g depending on deposits.
The surface areas of five sepiolites, all varying in crystallite size, were measured on heating, and were compared with a model calculation. A sharp decrease in the surface area, due to crystal folding, was observed between 200° and 400°C. Both before and after the folding, each sepiolite sample had peculiar values. Our model sufficiently explains this difference in surface areas among the samples. In the model, which is based on the Brauner-Preisinger structural model, surface area is a function of the crystallite size and the ratios of the coverage for nitrogen adsorption on both the internal and external surfaces. These ratios of the coverage can be inversely estimated from the model. The ratios of the coverage on the internal surface are less than 0.19, and that on the external surface between 0.7 and 1.0.
]]>Retention studies of the cobalt-goethite system were carried out using synthetic, star-shaped and lath-shaped pure, Al-, Cd-, Cu- and Si-associated goethites. Aluminium and Si are commonly occurring foreign elements in natural goethites. The goethites were prepared by coprecipitating Fe and the foreign element under controlled conditions and characterized by X-ray diffraction, transmission electron microscopy, specific surface area determination and 2 M HCl extraction. The foreign-element associated goethites contained ∼3, ∼5 and ∼9 mole % Al, ∼4 mole % Cd and ∼3 mole % Cu incorporated by isomorphous substitution but only ∼0.4 mole % of probably occluded Si. Crystal size and shape but also number of defects and domains, and hence specific surface area, unit-cell dimensions and reactivity towards 2 M HCl, exhibited great variability among the goethites. Accordingly the amounts of Co sorbed from initially 10−7 M Co in 0.1 M Ca(NO3)2 in relation to pH (3–8) and reaction time (2–504 h) were very different for the eight goethites. The affinity of Co is highest for Cd- and lowest for Cu-goethite. These samples also form the extremes regarding time-dependent sorption with Cu-goethite showing the smallest and Cd-goethite the largest increase in sorption with increasing reaction time. The Co uptake was not caused by precipitation Co(III) oxides due to Co(II) oxidation, since oxygen exclusion during sorption had no effect on the amount of Co sorbed. The amounts of sorbed Co extracted by 2 M HCl decreased with increasing sorption time but 40–87% of sorbed Co remained unextracted after 48 h, most in Cu-goethite and least in lath-shaped pure goethite. The strong retention suggests Co uptake by diffusion into micropores and fissures resulting from structural defects and intergrowths. The diffusion coefficients range from 3·10−19 to 6·10−17 cm2/s with the highest values for Al- and Si-associated goethites emphasizing the importance for Co immobilization, and hence availability, of foreign-element associations in goethite.
]]>In a previous paper, we used powder X-ray diffraction and changes in magnetic susceptibility to argue the importance of pedogenic maghemite to soils and the efficacy of the chemical extractant citrate-bicarbonate-dithionite (CBD) to preferentially remove pedogenic maghemite from soil samples while not removing coarse-grained magnetite. Although X-ray diffraction provides strong support for this contention, Mössbauer spectroscopy is the method of choice for determining the oxidation state of iron in minerals and for inferring mineralogy of the iron oxide phases. Our objective in this work was to seek confirming evidence of the importance of maghemite as a pedogenic mineral and the usefulness of the CBD procedure in separating pedogenic maghemite from lithogenic magnetite. We present Mössbauer data on magnetic fractions from pre- and post-CBD treated soil samples. Six of the 10 samples had only maghemite as the sextet component and after CBD treatment, four lost between 96 and 100% of the magnetic susceptibility. Two samples were interpreted as highly oxidized magnetite or a mixture of magnetite and maghemite. We cannot distinguish between these with Mössbauer spectroscopy. In the remaining two samples, iron existed as hematite, ilmenite, magnetite and minor (<10%) amounts of maghemite. Our results provide additional support for pedogenic maghemite in soils and for the preferential removal of maghemite by the CBD procedure.
]]>Like any other part of the world, Africa is not immune to the intermingling of cultures and civilizations, heritages and horizons, the endogenous and the exogenous, knowledge and imagery. The effects of new communication and information technologies, which still remain the privilege of a minority of political and intellectual elites, cannot conceal the far more profound transformations and reconfigurations that characterize its societies and cultures.
]]>Is ‘knowledge society’ yet another empty slogan? More than ever, ‘knowledge is power’. But we can hardly affirm that the society we live in is based on the vigour of knowledge. The market price placed on knowledge fails to provide it with the needed qualitative impetus. Inequities remain the blind spot of technological systems. To be sure, we are living in an information society at higher scales of exchange, with ‘a great deal of information, but little knowledge’. We may indeed be restoring a sort of enlightened despotism of a technologically neo-positivistic type, a realm of experts whose ‘know-how’ is but another term for ‘doing without knowing’. In a truly democratic sense, the knowledge society is a basic human right. Knowledge is nourished in society. Conversely, societies find in knowledge a compass for their peaceful co-existence.
]]>On our planet only the American continent has had the privilege, or the unhappiness perhaps, of being subjected to a sort of accounting of “anniversaries” or, let us say, “centennials.” But this does not mean, for all that, that these anniversaries serve to commemorate its birth. Geologists tell us the continents were formed hundreds of millions of years ago, making the commemoration of the American continent relatively recent. Moreover, the origins of this custom are foreign to it and are imbued, it must be said, with perspectives that are by all evidence “Eurocentric.” Curiously, no one took any notice of the first or the second centennial of the American continent.
]]>Porto-Novo (Benin), 19-21 September 2002. A conference on ‘The encounter between rationalities’, jointly organized by the Centre Africain des Hautes Etudes, the UNESCO network ‘Paths of Thought’ and the International Council for Philosophy and Humanistic Studies (ICPHS), took place there on the occasion of its 26th General Meeting. Seventy-two delegates from 33 countries. An ambitious academic programme, which, like all such programmes, we knew quite well we would never be able to cover, had been drawn up in four sections:
]]>The sorption properties of carbon-composite materials based on montmorillonite and hydrotalcite matrices have been studied using nitrogen adsorption isotherms and inverse gas chromatography. Carbon composite materials derived from both types of inorganic precursors contain pore structure accessible for adsorbate molecules. Adsorption capacity per unit mass of these composite adsorbents is larger in the case of hydrotalcite than in montmorillonite-based materials. Exposing these materials to ambient conditions results in their hydration. Subsequent water removal by heating under vacuum increases nitrogen adsorption capacity, which is explained by the opening of the adsorption space. The water content of hydrated samples and its effect on adsorption capacity is greater for the case of hydrotalcite-based materials. No direct relationship between carbon content and adsorption properties of the materials studied is observed.
]]>The interactions of the following three kinds of racemic and enantiomeric cobalt(III) chelates with montmorillonite and saponite are studied: [Co(en)3]3+ (en = ethylenediamine), [Co(diNOsar)]3+ (diNOsar = (1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6,6,6]-eicosane)cobalt(III))and [Co(diAMsar)]3+ (diAMsar = (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo-[6,6,6]eicosane)-cobalt(III)). At neutral pH, these complexes are adsorbed as a trivalent cation up to 90%–100% of the cation exchange capacity of a clay. No difference is observed in the maximum adsorption amount between the racemic and enantiomeric isomers. The basal spacings of the clay-chelate adducts are determined by the X-ray diffraction measurements of non-oriented powder samples: 14.3 Å for [Co(en)3]3+ montmorillonite, 16.5 Å for [Co(diNOsar)]3+ montmorillonite, and 16.9 Å for [Co(diAMsar)]3+ montmorillonite. The results imply that the chelates form a monolayer in the interlayer space. From the one-dimensional Fourier analyses of the diffraction pattern of [Co(diNOsar)]3+ montmorillonite, the chelate is concluded to be adsorbed with its three-fold symmetry axis in parallel with the layer surface. This is in contrast with the previous results of [Ru(phen)3]2+ and [Ru(bpy)3]2+, which are adsorbed with their three-fold symmetry axes perpendicular to the surface. The conclusion is consistent with the angular dependence of the infrared absorption spectrum of the film of the adduct.
]]>The dissolution of two Ca2+-exchanged nontronite samples has been studied in 10% HCl. Early acid-dissolution studies (Osthaus, 1954) have indicated that after two hours of dissolution most of the octahedral Fe3+ (VIFe3+) would be removed leaving mainly tetrahedral Fe3+ (IVFe3+) in the nontronite structure. In the present study, 57Fe Mössbauer spectra of acid-treated samples were recorded and fitted with two octahedral Fe3+ (2 × VIFe3+) and two octahedral and one tetrahedral (2 × VIFe3+, 1 × IVFe3+) doublet models. The Mössbauer spectra of acid-treated Garfield nontronite samples could be adequately fitted with two-doublet models but acid-treated Hohen Hagen nontronite samples could not. Isomer shift and quadrupole splitting values obtained from the two-doublet models corresponded to VIFe3+ and not IVFe3+, as was suggested by the Osthaus (1954) experiment. When an IVFe3+ doublet was included in the model used to fit the Mössbauer spectra of acid-treated Garfield nontronite samples, a slight increase in the intensity of the IVFe3+ doublet occurred with increasing dissolution, but this was much lower than indicated by Osthaus (1954). No trend in the intensity of the IVFe3+ doublet was observed for acid-treated Hohen Hagen nontronite. Therefore, acid treatment appears to remove VIFe3+ and IVFe3+ from the nontronite structure at about the same rate. Mössbauer spectroscopy, infrared spectroscopy and X-ray powder diffraction data indicate that the nontronite that remains undissolved following acid treatment is structurally similar to the untreated nontronite.
]]>The “Formation Rouge” from the Jbel Rhassoul in Morocco is composed of detrital sediments which have a lacustrine origin. The clays contained in the less than 2 µm fraction of the sediments are detrital phengites and illites, illite/smectites or smectites, and palygorskite. Due to the presence of well preserved long fibers, the palygorskite could not have been transported. They are authigenic and must have formed directly by precipitation from solutions rich in Mg and Al. The detrital illites are impoverished in K and tetrahedral Al. The illite/smectites or smectites, on the contrary, are K-rich but have a low tetrahedral charge. They are also richer in Mg and Fe and have a different crystal size, composition, and crystallinity from the illites. They most probably formed by crystallization, similar to the palygorskites, directly from the solution. The Al could have been provided by the detrital illite, which may have been unstable in an alkaline environment and released K and Al to the solutions.
]]>The level of Fe impurities in 2 well-crystallized kaolinites was modified (by addition or chemical removal treatment) to analyze the Fe influence in the aluminosilicate zeolite synthesis.
The original and modified clays were heat-treated in order to change their reactivity for zeolite A synthesis, and their thermal transformations were studied by X-ray diffraction (XRD), determination of point of zero charge (PZC) and infrared (IR) techniques. It was established that many structural changes took place, regardless of the Fe clay content. Furthermore, the presence of Fe species in alkaline solution or in the solid phase did not seem to greatly influence the zeolite crystallization, because only small differences in the conversion values among samples with different Fe contents were registered. The crystallization process seemed to be related mainly to AI coordination changes produced by the thermal and Fe removal treatments used.
]]>The clay mineralogy of an oxisol-saprolite overlying serpentinite and underlying basalt was studied with different techniques to evaluate the clay mineral transformation that occurred and to understand the origin of Fe3+-rich smectite. The saprolite zone of the oxisol, up to 30 m thick, contains smectites of the montmorillonite-beidellite and montmorillonite-nontronite series, as well as illite, chlorite, talc, and goethite or amorphous oxyhydrates. Illite is mainly concentrated in the upper 50 cm thick zone underlying the basalt layer and chlorite-content increases toward altered serpentinite at the base. Minor amounts of nontronite formed mostly toward westward exposures where the hot contact layer between serpentinite and basalt is only 20 cm thick. Greene-Kelly Li-tests revealed that all samples contain montmorillonite, but one sample shows the presence of a minor amount of beidellite.
Parent rocks are a mixture of mainly mica schist (the source of beidellite), and minor serpentinite in different percentages and laterally distributed. These rocks were intensely weathered under humid climatic conditions. Silica was concentrated as amorphous transparent (pure silica) cobbles and milky quartz pebbles, and originated from geothermal solutions rising through the Ovaclk thrust fault. The Mg partly formed chlorite. Ferrian smectites in serpentinites were derived obviously from the Mg-rich minerals but Mg is lost much more rapidly than Si during the formation of the clay deposit. The structural formula of the most Fe-rich smectite samples from the study area is (Si6.60−7.10Al1.40−0.90)(Al2.54−1.22Mg0.32−0.92Fe3+1.18−1.68−Ti0.06−0.04)(Ca0.16−0.10Na0.02K0.02−0.12)O20(OH)4. This composition is within the range recorded for the ferrian montmorillonite-beidellite series, with very little vermiculite forming the oxisol-vertisol horizon.
]]>Transmission X-ray diffraction (XRD) of C6–16 alkylammonium ion-exchanged montmorillonite SAz-1 with Ag-behenate as an internal standard provided accurate estimates of d(001) values of the alkylammonium ion-exchanged montmorillonite. Inspection of d(001) values were made to assess the possible formation of gauche conformers (alternate arrangements of the molecules) in the interlayer and to determine the critical carbon chain length, nC. Using conventional constraints for nC(I′) and nC(II) equal to 1.36 and 1.77 nm, respectively, provided ambiguous nC(I′) and nC(II) values. The dependence of full-width at half-maximum values on nC allowed better estimates of nC(I′) and nC(II) because “integral” and “non-integral” peak characteristics relating to interstratification could be included in the assessment.
The effect of inaccurate estimates of nC(I′) and nC(II) values on calculated interlayer cation exchange capacity (Ci) using two conventional concepts of calculation were compared. It was found that a procedure based on the summation of fractions of the layer charge gave relative errors of Ci <2%, even where the number of carbon atoms corresponding to both nC(I′) and nC(II) differed by ± 1 nC from the correct values. This method of calculation of Ci is recommended when reliable values of Ci are needed.
]]>A new model is proposed to explain, within the framework of the theory of spiral growth of Frank, the formation on inhomogeneous mica polytypes. This model relates the interaction and cooperative growth of two components (spirals and/or crystals) to produce a new stacking sequence. Depending on the relative orientation between the two components, a mismatch of the interlayer positions occurs, which is compensated through either a growth defect or a crystallographic slip at the octahedral (O) sheet. Both these adjustments transform the Ml layer into the M2 layer. These two types of layers have the same chemical composition but differ in cation distribution in the O sheet. The coalescence and cooperative growth of crystals occurs in fluid-rich environments and is most frequent in druses and volcanic fumaroles. These environments favor the inhomogeneous polytypes, especially those with complex stacking sequenc¬es. In addition, the Ml → M2 transformation is most probable in micas with an oxybiotitic composition, where the removal of the OH dipole strengthens the interlayer bonding and the presence of high-charge cations destabilizes the O sheet. Three examples of inhomogeneous polytypes of titaniferous oxybiotite from Ruiz Peak (a volcanic environment where many inhomogeneous polytypes have been reported) are presented.
]]>In soil environments, the surfaces of clay minerals are often coated with hydrolytic products of Al. However, limited information is available on the effect of hydroxyaluminum coatings on the interlayering of enzymes for montmorillonite. The objective of this study was to compare the adsorption of tyrosinase onto montmorillonite as influenced by levels of hydroxyaluminum coatings. Tyrosinase is one of the strongest catalysts in the transformation of phenolic compounds. Adsorption of tyrosinase onto Ca-montmorillonite (Ca-Mte) and different hydroxyaluminum-montmorillomte complexes (Al(OH)x-Mte), containing 1.0, 2.5 and 5.0 mmol coated Al/g clay, was studied both in the absence and in the presence of a phosphate buffer at pH 6.5 and 25°C. Except for Ca-Mte in the absence of phosphate where the adsorption isotherm was of C type (linear), the adsorption isotherms were of L type (Langmuir). More tyrosinase molecules were adsorbed onto Ca-Mte than onto the Al(OH)x-Mte complexes, both in the absence and in the presence of phosphate. This indicated the easy accessibility of the enzyme to the uncoated Ca-Mte surfaces. The presence of phosphate did not significantly affect the amount of tyrosinase adsorbed onto Ca-Mte, but substantially reduced the adsorption of tyrosinase onto Al(OH)x-Mte complexes. The higher the level of hydroxyaluminum coatings, the lower the amount of tyrosinase was adsorbed. Because of their affinity to the aluminous surfaces, phosphate ions evidently competed strongly with tyrosinase for Al(OH)x-Mte complexes adsorption sites. The intercalation of tyrosinase by Ca-Mte was indicated by the increased d-spacing of the complex as the amount of the enzyme adsorbed increased. The infrared spectra of tyrosinase-Ca-Mte complex showed that the amide II band of tyrosinase at 1540 cm-1 was practically unaffected by adsorption. The amide I band at 1654 cm-1 was shifted toward a higher frequency, indicating a slight perturbation in the protein conformation. This perturbation became more noticeable in the presence of Al(OH)x-Mte complexes. The data indicated that hydroxyaluminum coatings play an important role in retarding the adsorption of tyrosinase by montmorillonite, and phosphate effectively competes with tyrosinase for the adsorption sites on Al(OH)x-Mte complexes.
]]>In the search for new applications of natural silicates, various F− treatments have been applied to sepiolite to increase its acidic properties and for use as a catalyst in reactions occurring via carbonium ions. Two types of treatments including hydrofluoric acid (HF) at different concentrations and 2 N NH4F have been utilized and the physicochemical characteristics of the resulting materials studied using standard techniques. The X-ray diffractogram (XRD) patterns indicate a decrease in crystallinity of the original material as well as the appearance of amorphous silica. SEM micrographs showed a shortening and aggregation of the sepiolitic fibers. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), thermogravimetric analysis/differential thermal analysis (TGA/DTA), N2 adsorption-desorption isotherms and Hg intrusion were used to study the changes occurring in the structure, surface area and pore distribution of samples and acidity was evaluated by IR and thermoprogrammed desorption (TPD) of adsorbed ammonia and pyridine. It was found that acidity increased in most of the samples after anionic and cationic interchange between the activating agents and the surface sites, or extralattice cations. Additionally, structural changes induced by treatments modified the Brönsted and Lewis acidity. Mild treatments with ammonium fluoride are more effective than HF treatments in acidity generation.
]]>On our planet only the American continent has had the privilege, or the unhappiness perhaps, of being subjected to a sort of accounting of “anniversaries” or, let us say, “centennials.” But this does not mean, for all that, that these anniversaries serve to commemorate its birth. Geologists tell us the continents were formed hundreds of millions of years ago, making the commemoration of the American continent relatively recent. Moreover, the origins of this custom are foreign to it and are imbued, it must be said, with perspectives that are by all evidence “Eurocentric.” Curiously, no one took any notice of the first or the second centennial of the American continent.
]]>Porto-Novo (Benin), 19-21 September 2002. A conference on ‘The encounter between rationalities’, jointly organized by the Centre Africain des Hautes Etudes, the UNESCO network ‘Paths of Thought’ and the International Council for Philosophy and Humanistic Studies (ICPHS), took place there on the occasion of its 26th General Meeting. Seventy-two delegates from 33 countries. An ambitious academic programme, which, like all such programmes, we knew quite well we would never be able to cover, had been drawn up in four sections:
]]>The rule of the Caesars, which for 500 years held sway over an empire of 5 million square kilometres of land, today distributed among 30 states, was very different from the monarchies, such as the medieval and modern ones that are more familiar to us. Before the Revolution French kings inherited a kingdom that was their family's property; this fiction concerning family and inheritance was calmly accepted and perpetuated with astonishing ease. Roman emperors, on the other hand, had a high-risk job; they did not occupy the throne as its owner but merely as the appointee of the community, which tasked them with governing the Republic, in the same way, I am informed, as the caliphs were appointees of the community of the devout and with the same bloody conflicts each time the ruler changed.
]]>Is it only yesterday's humanism, whether religious or secular in origin, that is dying - and is it really dying? - or is it more profoundly the very paradigm of humanity? At least it is worth asking the question. Do we not hear on every side today that everything is ‘constructed’ and ‘formated’? No inherited moral standard now seems acceptable, nor any reference to any sort of human nature or naturality. The only idea that henceforth finds acceptance is that of the infinite plasticity of the human, leaving individuals free to shape themselves as they wish beyond any commonly received standard, since only defiance of the norm seems to be the source and proof of freedom.
]]>I hope I will not be accused of mental colonialism by attributing to Europe the role which belongs to it historically: that of the Self, which leaves the position of the Other for us. Consequently, this text ought to begin with the view taken of the Other (the European view of the Brazilians) and continue with the view held by the Other (the Brazilian view of the Europeans).
]]>The topic of this article is the self-less self (selbst-lose Selbst) and more particularly this self in its connection with the problem of language. There exists a movement of the self-less self from itself toward itself. This movement also occurs as the liberation from language toward language; language reaches into the core of being self because our understanding of self and of the world is linguistically constituted. Similarly the fundamental conversion - as the occurence of the breakthrough (by means of the I-am-myself) to the truth of the self - is nothing else than an original word event. The self-less, the true self says at this moment: “I am myself by not being myself (Ich bin, indem ich nicht ich bin, ich).” In order to gain a better understanding we now start from the problem of language.
]]>Today, with the digitisation of texts, sounds and images and their circulation on the Internet, we are deploying new techniques for storing knowledge which will increasingly supplement and even replace older memory recording systems, such as books, vinyl discs, and photographs on celluloid. It looks as if the extent of these changes will be far reaching. And if, as many believe, the practical methods of inscribing thought have an impact on the way it is developed through the writing and reading process, we can understand why the changes now taking place could profoundly affect our ways of thinking. Here we have gathered together specialists in ancient means of recording memory - clay tablets, papyrus rolls and manuscripts - along with experts from the electronic age - originators of man-machine interfaces, enterprise knowledge management systems, hypermedia and intelligent agents - with the purpose of elucidating the present by reference to intellectual technologies of the past.
]]>The epic, one of the oldest forms of poetic expression, came into being and evolved in time immemorial, long before the appearance of writing - the advent of which, while helping to fix oral traditions since the dawn of history, has at the same time sapped these traditions of their freshness. Not until methods of recording and reproduction were perfected was the oral epic restored to its full compass as a work of enduring dimensions.
]]>Is anthropology a science? To put the question today amounts to a reply in the negative. The representatives of the ‘true’ sciences are not alone in suggesting a conjunctural or crippling lacuna which would preclude membership by right of the prestigious world, which, however, the name ‘humanistic sciences’ seems to demand. We should remember that some years ago Claude Lévi-Strauss caused a shudder to run through his discipline by describing it as a ‘flattering imposture’. Since then denigration has spread constantly, and it no longer consists of deploring a slowness, an equivocation or a handicap which we would have the hope of remedying: it is definitely a fatality which we are from now on invited to confirm.
]]>In the passage from the Enneads devoted to discussing and defining the nature of time, it is written that first one must experience eternity, which, as everyone knows, is the model and archetype of time. This initial warning, which is especially serious because we trust in its sincerity, appears to wipe out all hope of finding common ground with its author.
Jorge Luis Borges, History of Eternity
So let us leave the Platonists to wander off down a blind alley. Poor simpletons, they think they will find the secret of discourse about time in the link with eternity. Whereas I, who am powerless in the face of eternity, would prefer to ask: what link can be retained, in discourse about time, between past, present, and future? If there is some link, can the three kinds of time break free of their mutual bonds? Can predicting the future, a time that will be but has never existed before, be disconnected from what determines the future as a product of what already exists and what has already existed? Can the past be what it once was or will it always be what each age decides it should have been?
]]>The question of whether there are cultural borders between East and West is thrown up by the clear awareness of a process exacerbating worldwide contradictions which politicians call the Clash of Civilizations. However, UNESCO proposes that this opposition should be transformed into a more peaceful Dialogue of Civilizations. It is obvious that in both cases we need to disentangle the causes of differences that undoubtedly have ancient roots.
]]>Brazil, land of miscegenation (métisse). An indisputable fact and an unending process. But how should we understand its genesis and how should we, while respecting the requirements of a historiography worth the name, interpret it in terms of our hopes for the future? This is the horizon binding these reflections, which is to be put in perspective in the studies published in this issue of Diogenes.
Foregrounding miscegenation, and understanding its origins, has been one of the constant themes among the most distinguished practitioners of Brazilian thought since the 1930s, and has been accepted, indeed demanded, since the 1920s by the artistic and literary movement known as ‘modernism’, of which one of the major figures was the São Paulo writer, Mário de Andrade. Gilberto Freyre (1900–1987), who would now have been a hundred years old, comes particularly to mind, as does Sergio Buarque de Holanda (1902–1982). Freyre made history with the publication of his two first works, Casa Grande & senzala [Masters and Slaves] of 1933 and Sobrados e mucambos of 1936. The same year Buarque de Holanda published his Raízes de Brasil [Roots of Brasil]. Motivated by the desire to understand their country, its shaping and – with some kind of concern as to identity – their own origins, both had been led to pave the way for what might be called an ‘open’ sociology, which immediately acquired a strongly anthropological character with Freyre and quickly incorporated increasingly historical aspects with Buarque de Holanda.
]]>Our world has just discovered another world [ … ] I am much afraid
[ ... ] that we will have sold it our opinions and our arts very dear.
Michel de Montaigne, Essays, III, 1588
The year 1992 saw many important cultural commemorations take place, of which the most important, the fifth centenary of the “discovery” of America, seemed to eclipse, at least on the American continent, the four hundredth anniversary of the death of Montaigne (1533-1592). It therefore does not seem inappropriate to question the view of the author of the Essays concerning the theme, “much fussed over” by ideologues on all sides, of the “encounter,” as memorable as it is debatable, between the “New” world and the “Old”.
]]>Suspensions were produced by mixing Na-saturated, Upton montmorillonite with aqueous solutions containing different concentrations of 1,4-dioxane. Each suspension was deposited on a porous ceramic filter in an environmental chamber, and the solution was expressed from it by admitting gaseous helium to the chamber at a slightly elevated pressure. The chamber was fitted 1) with beryllium windows so that X-rays could be transmitted into and out of it and 2) with a drain so that the expressed solution could be conducted to the outside atmosphere. Once a filter cake had formed on the filter, the pressure of the gaseous helium was raised in successive increments and, after each increment, the c-axis layer spacing(s) was determined by X-ray diffraction. Increasing the concentration of 1,4-dioxane caused some of the fully expanded layers to collapse to the partially expanded state (c-axis spacing = 15 Å) and appeared to cause the remaining fully expanded layers to move farther apart, especially at the higher pressures. Alternative explanations were given for these apparently contradictory results.
]]>Being professionally interested in African languages, there is no way in which we could try to hide our rather selfish motive in hoping for the survival of African languages, and as many as possible at that. The disappearance of any African language means to us scholars the final, irrecoverable loss of an important empirical resource, not only for linguistic studies, but also for studies on the history and culture of a people. Not many outside the academic circle, however, will have heartaches over such matters.
]]>Alumina-pillared montmorillonite is prepared by intercalation of polyoxyhydroxy aluminum cations (Al137+) of a natural montmorillonite from Dimitrovgrad, Bulgaria. Transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and surface area (BET) methods are used to study the untreated and pillared forms of the montmorillonite. A structural model involving deformed Al13 pillars is proposed. Four pillar types are derived and these pillars are uniformly distributed over the interlayer-cation positions of montmorillonite. Calculated electron diffraction patterns were simulated using the multi-slice method. The structural model explains the increased ordering along the c axis of the pillared form compared with the untreated montmorillonite. The model explains the structure of a pillared montmorillonite with different distributions of the pillars in the interlayer. The proposed model is consistent with the observed data.
]]>Testing shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).
]]>Infrared spectroscopy is used to distinguish between octahedral and tetrahedral substitutions in an interstratified illite-smectite clay. The Hofmann-Klemen (Li) test suggests that the AlMg□ and FeMg□ octahedral vacancies are preferentially occupied by Li after thermal treatment at 250°C. The ammonium (Chourabi-Fripiat) test reveals the beidellitic character by the formation of two OH stretching modes upon deammonation. The illitic layers are not affected since K is not exchangeable.
]]>Earlier interpretations of the conversion of the virgin smectite of the Ordovician Kinnekulle K-bentonites into the present mixed-layer illite/smectite imply that it took place through charge increase of the smectite with subsequent uptake and fixation of potassium. Recent analyses show that the layer charge of the smectite component of the I/S is in fact low and they suggest that neoformation of a separate illite phase took place. Pytte's kinetic model gives good agreement with the actual conversion rate for an activation energy of about 25–27 kcal/mole, depending on the adopted rate parameters, temperature history and assumed potassium source. In the Kinnekulle case the rate-controlling factor appears to have been the supply of potassium, which is concluded to have required large-scale, heat-induced groundwater convection.
]]>The chemical and the mineralogical composition of a group of pumiceous tuffs associated with recent salic volcanic episodes from Tenerife (Canary Islands) have been studied. The investigation focused on the two main types of pyroclastic deposits of the zone: ash-flows and ash-falls. The samples can be classified chemically as trachytic and phonolitic rocks with an intermediate silica content and a high percentage of alkali cations (Na+ and K+). The mineralogical composition, determined by X-ray diffraction, scanning electron microscopy, and optical microscopy, shows the occurrence of zeolites (mainly phillipsite, with lesser chabazite and analcime), associated with the parent glass. K-feldspar (sanidine) and calcite are accessory minerals. Zeolites are significantly more abundant in the ash-flow deposits. Zeolite formation by hydrothermal weathering in closed-system conditions varies according to the nature and the origin of the pyroclastic deposits. Tenerife phillipsites differ from typical diagenetic, lacustrine, and deep-sea phillipsites, both in chemical and mineralogical features. Alkali cations exceed divalent cations in the unit-cell that, assuming a monoclinic symmetry, has the following parameters: a = 8.46–10.55 Å, b = 14.21–14.40 Å, c = 7.80–8.70 Å, and β = 105°–110°.
]]>Clay minerals in shales from cores at Site 808, Nankai Trough, have been studied using X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and analytical electron microscopy (AEM) to compare the rates and mechanisms of illitization with those of coeval bentonites, which were described previously. Authigenic K-rich smectite having a high Fe content (∼7 wt. %) was observed to form directly as an alteration product of volcanic glass at a depth of ∼500 meters below seafloor (mbsf) with no intermediate precursor. Smectite is then largely replaced by Reichweite, R, (R = 1) illite-smectite (I-S) and minor illite and chlorite over depths from ∼550 to ∼700 mbsf. No further mineralogical changes occur to the maximum depth cored, ∼1300 m. Most smectite and I-S in shales are derived from alteration of glass, rather than being detrital, as is usually assumed. Discrete layer sequences of smectite, I-S, or illite coexist, indicating discontinuities of the transformation from smectite to (R = 1) I-S to illite. Authigenic Fe-rich chlorite forms concomitantly with I-S and illite, with the source of Fe from reactant smectite.
Smectite forms from glass with an intermediate precursor in coeval bentonites at approximately the same depth as in shales, but the smectite remains largely unchanged, with the exception of exchange of interlayer cations (K → Na → Ca) in response to formation of zeolites, to the bottom of the core. Differences in rates of illitization reflect the metastability of the clays. Temperature, structure-state, and composition of reactant smectite are ruled out as determining factors that increase reaction rates here, whereas differences in water/rock ratio (porosity/permeability), Si and K activities, and organic acid content are likely candidates.
]]>A synthetic octahedral-site-vacancy-free annite sample and its progressive oxidation, induced by heating in air, were studied by powder X-ray diffraction (pXRD), Mössbauer spectroscopy, nuclear reaction analysis (NRA), Raman spectroscopy, X-ray fluorescence (XRF) spectroscopy, gas chromatography (GC), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM), and size-fraction separation methods. For a set heating time and as temperature is increased, the sample first evolves along an annite-oxyannite join, until all H is lost via the oxybiotite reaction (Fe2+ + OH− ⇌ Fe3+ + O2− + H↑). It then evolves along an oxyannite-ferrioxyannite join, where ideal ferrioxyannite, KFe3+8/3□1/3AlSi3O12, is defined as the product resulting from complete oxidation of ideal oxyannite, KFe3+2Fe2+AlSi3O12, via the vacancy mechanism (3 Fe2+ ⇌ 2 Fe3+ + [6]□ + Fe↑). A pillaring collapse transition is observed as a collapse of c near the point where and all OH groups are predicted and observed to be lost. Quantitative analyses of H, using NRA, GC, and Raman spectroscopy, corroborate this interpretation and, in combination with accurate ferric/ferrous ratios from Mössbauer spectroscopy and lattice parameter determinations, allow a clear distinction to be made between vacancy-free and vacancy-bearing annite. The amount of Fe in ancillary Fe oxide phases produced by the vacancy mechanism is measured by Mössbauer spectroscopy to be 11.3(5)% of total Fe, in agreement with both the theoretical prediction of 1/9 = 11.1% and the observed TGA weight gain. The initiation of Fe oxide formation near the point of completion of the oxybiotite reaction () is corroborated by pXRD, TGA, Raman spectroscopy, and appearance of an Fe oxide hyperfine field sextet in the Mössbauer spectra. The region of Fe oxide formation is shown to coincide with a region of octahedral site vacancy formation, using a new Mössbauer spectral signature of vacancies that consists of a component at 2.2 mm/s in the [6]Fe3+ quadrupole splitting distribution (QSD). The crystal chemical behaviors of annite-oxyannite and of oxyannite-ferrioxyannite are best contrasted and compared to the behaviors of other layer-silicate series in terms of b vs. [D] (average octahedral cation to O bond length). This also leads to a diagnostic test for the presence of octahedral site vacancies in hydrothermally synthesized annite, based on a graph of b vs. Fe2+/Fe. The implications of the observed sequence of thermal oxidation reactions for the thermodynamic relevance of the oxybiotite and vacancy reactions in hydrothermal syntheses are examined and it is concluded that the oxybiotite reaction is the relevant reaction in the single-phase stability field of annite, at high hydrogen fugacity and using ideal starting cation stoichiometry. The vacancy reaction is only relevant in a multi-phase field, at lower hydrogen fugacity, that includes an Fe oxide equilibrium phase (magnetite) that can effectively compete for Fe, or when using non-ideal starting cation stoichiometries.
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