Earthly civilization has now entered a phase of development which requires urgent need of imagination to discern its eventual evolution.

Demographic problems occupy a considerable place in global development. Numerous authors interested in the future of the planet have referred to the important factor of population increase. Nevertheless their attitudes toward demographic problems, the manner in which they conceive their own roles, their forecasts are all diverse and reflect a wide range of ideas from serene optimism to nihilistic pessimism.

A hydrated alumino-phosphate mineral was identified in thin, kaolinitic clay beds of the Cretaceous Dakota Group and the overlying Mowry Shale in the Dakota hogback west of Denver, Colorado. It occurs as 1–3-μm size euhedral crystals and makes up as much as 15% of the rock. Sr is by far the dominent divalent cation present, ranging from 9.4 to 13.1%, confirming the X-ray powder diffraction identification of this mineral as goyazite, the Sr member of the plumbogummite group. The characteristic pseudo-cubic, rhombohedral morphology of this mineral is plainly visible in scanning electron micrographs. On the basis of its euhedral morphology and its occurrence in volcanic ash-derived kaolin beds, the goyazite probably formed during early diagenesis, before or during the alteration of the ash, and before much compaction of the beds.

The adsorption on montmorillonite of two monovalent organic cations, methylene blue (MB) and thioflavin T (TFT), was studied in four different situations: (1) separate adsorption of MB or TFT; (2) competitive adsorption of TFT and Cs; (3) competitive adsorption of the two organic cations from their equimolar solutions; and (4) adsorption of TFT on a clay whose cation-exchange capacity (CEC) had been previously saturated with MB. MB and TFT adsorbed to as much as 120% and 140% of the CEC, respectively. Cs did not appear to compete with TFT for the adsorption sites of the clay. TFT molecules adsorbed more strongly than those of MB and displaced them from the clay surface. A model was developed to evaluate the strength of the clay-organic cation interactions. The specific binding of the cations to the negatively charged surface, determined by solving the electrostatic equations, appears to account for adsorption exceeding the CEC and formation of positively charged complexes, which are due to non-coulombic interactions between the organic ligands.

The charge reversal predicted by the model beyond the CEC of the clay was confirmed by microelec-trophoretic experiments. Particles in a sample of montmorillonite loaded with 50 meq TFT/100 g clay moved to the positive electrode, whereas in samples containing the two dyes, MB and TFT, coadsorbed at a total concentration of 100–120 meq/100 g clay, the particles moved to the negative electrode. Binding coefficients describing the formation of neutral and charged complexes of TFT and the clay were larger than those for MB and the clay, thereby explaining the preferential adsorption of TFT observed experimentally. The binding coefficients for the formation of neutral complexes of either MB and TFT and the clay were more than six orders of magnitude larger than those previously reported for inorganic monovalent cations.

The formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 Å wide and spaced 200 Å apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks < 50 Å in diameter allow Na, Al, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20–50 Å wide and 1–7 layers thick, form bridges 50–100 Å long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 × 100 × 200 Å (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.

Dilute aqueous solutions of quinoline were contacted with Na-montmorillonite to elucidate the sorption process of the neutral and protonated species. Sorption occurs via a combination of ion exchange and molecular adsorption and yields S-type isotherms. Exchange between the quinolinium ion (QH+) and Na can be described by means of Vanselow selectivity coefficients and a thermodynamic exchange constant (Kex). Due to the apparent adsorption of the neutral species at high mole fractions (x) of the solid phase, the thermodynamic standard state was defined as 0.5 mole fraction. The selectivity at pH ~4.95 of the QH+ species over Na (at XQH+ = 0.5) was determined to be Kv = 340. At pH ≥ 5.5 surface mole fractions of 0.5 could not be obtained without adsorption of the neutral species. This study suggests that at dilute solution concentrations quinoline is sorbed preferentially as the cation even at pHs ≫ pKa. A critical surface-solution concentration is apparently necessary for adsorption of the neutral species.

Point defect centers in hydrothermal kaolinite have been investigated using electron paramagnetic resonance (EPR). Kaolinite was sampled in petrographically well-defined materials coming from uranium-rich hydrothermally altered volcanic tuffs (Nopal I uranium deposit, Chihuahua, Mexico), which show extensive kaolinization and an intense redistribution of uranium. Several kaolinite parageneses were defined according to their origin (fissure fillings and feldspar pseudomorphs); their location relative to the U6+ mineralization at the scale of the deposit (mineralized breccia pipe vs. barren surrounding rhyolitic tuffs), and at the scale of mineral assemblages; and their crystal chemistry.

Two types of centers of axial symmetry were identified (A- and A′-centers) and represent positive holes trapped on apical oxygens (Si-O−-centers). A-centers were stable to 400°C, whereas A′-centers annealed at 350°C. A relation between defect-center concentration and U content demonstrates that natural irradiation was responsible for these centers. On the other hand, defect-center concentration was not directly linked to the origin (fissural or feldspar pseudomorph) or the crystal chemistry (structural order and substitutional Fe3+ content) of the kaolinite. According to petrographic data, and with respect to the relative thermal stability of A- and A′-centers, two successive irradiations of kaolinite were evidenced: (1) originally during crystallization of kaolinite from radioactive hydrothermal solutions, and (2) permanently when kaolinite was in contact with secondary U-silicates, which led to the formation of A′-centers.

Because of the short half-life of U, these two radiation-induced centers were created by short-lived elements of the U-decay series. As a consequence, variations of defect-center concentration possibly reflect variations in radioactive disequilibrium during the history of the alteration system. This provides a unique tool for tracing the dynamics of the transfer of radionuclides in the geosphere: kaolinite may be used as a sensitive in situ dosimeter, which may be useful in the fields of weathering petrology and nuclear waste management.

The fall of the nineteenth century abounded in discoveries of natural laws, that is, strict and unequivocal rules of the development of life. These laws stated for example that ontogeny of individuals repeats, or recapitulates, phylogeny of the species; that big and specialized forms originate in evolution from small and unspecialized ones, while the reverse is not true; that endothermic animals are larger-sized and more compact in cool than in warm climates, and so on. Louis Dollo, a Belgian palaeontologist, proposed the so-called law of irreversibility of evolution which stated that an organic structure lost in evolution cannot reappear with all the peculiarities of its design. This law seems indeed to be true but not particularly original. It was Heraclitus who first observed that one could not enter the same river twice. Dollo's law says essentially the same thing. The flow of evolutionary events combines so many processes in so many ways that past evolutionary events cannot recur exactly. “What is done, is done forever”. Time itself introduces asymmetry into the evolutionary process.

A green, Lithic Torriorthent soil derived from a celadonite-rich, hydrothermally altered basalt immediately north of the Mojave Desert region in southern California was studied to investigate the fate of the celadonite in a pedogenic weathering environment. Celadonite was found to be disseminated in the highly altered rock matrix with cristobalite, chalcedony, and stilbite. X-ray powder diffraction (XRD) showed the soil material to contain celadonite having a d(060) value of 1.510 Å, indicative of its dioctahedral nature. Very little smectite was detected in the parent material, whereas Fe-rich smectite was found to be abundant in the soil. The Fe-smectite and celadonite were identified as the sole components of the green-colored clay fraction (<2 µm) of all soil horizons. The soil clay showed a single d(060) value of 1.507 Å, indicating that the smectite was also dioctahedral and that its b-dimension was the same as that of the celadonite. Mössbauer spectroscopy showed that the chemical environments of Fe in the rock-matrix celadonite and in the smectite-rich soil clay were also nearly identical. These data strongly suggest a simple transformation of the celadonite to an Fe-rich smectite during soil formation.

Supporting evidence for this transformation was obtained by artificial weathering of celadonite, using sodium tetraphenyl boron to extract interlayer K. The intensity of the 001 XRD peak (at 10.1 Å) of celadonite was greatly reduced after the treatment and a peak at 14.4 Å, absent in the pattern of the untreated material, appeared. On glycolation of the sample, this peak expanded to 17.4 Å, similar to the behavior of the soil smectite. The alteration of celadonite to smectite is a simple transformation requiring only the loss of interlayer K. The transformation is apparently possible under present-day conditions, inasmuch as the erosional landscape position, shallow depth, and lack of significant horizonation indicate that the soil is very young.

John Rawls est souvent perçu comme un partisan de politiques redistributives visant à apaiser les conséquences d'une économie capitaliste qu'il ne remettrait pas en cause. Cet article montre qu'il s'agit là d'un préjugé et donne un aperçu de la transformation du paysage des entreprises qu'impliquerait une société juste aux yeux de Rawls. Nous commentons les régimes économiques qu'il esquisse dans son œuvre et rappelons que le libéralisme égalitaire a en vérité des implications profondes et souvent insoupçonnées en ce qui concerne la propriété et la gestion des entreprises. Pour Rawls, la démocratie de propriétaires implique que les citoyens possèdent tout au long de leur vie des parts sociales dans les entreprises tandis que le socialisme libéral suppose la nationalisation des moyens de production et la socialisation de leur gestion.

Low-angle X-ray powder diffraction (XRD) measurements of soil samples, made at controlled relative humidities, showed the presence of major reflections at 20–33, 10–27, and 7–8 Å. The first reflection, which increased in intensity but did not shift in spacing with decreasing relative humidity, represents curved smectite layers. This spacing was also observed by high-resolution transmission electron microscopy. The value of 10–27 Å for the second reflection, the 001 reflection of smetite, is unusually high, probably due to poorly stacked, irregularly curved layers. The 7–8-Å reflection originates from kaolinite or dehydrated halloysite, which also contain curved layers. The more curved the layer structure of the smectite, the more difficult it is to detect this phase; therefore the XRD relative peak heights are not directly proportional to the percentages of the smectite.

Sulfate adsorption on kaolinite was followed at 0.7 μeq/ml to 99 μeq/ml solution concentrations at 30°C and at pH 6.0, and the amount of OH~ ions released and the change in surface charge were determined. Sulfate was adsorbed at positive and neutral sites by displacing OH2 and OH− groups, respectively. Adsorption of sulfate occurred predominantly at positive sites at low (0.7 μeq/ml to 0.9 /μeq/ml) solution concentrations, whereas at higher solution concentrations, the proportion of the sulfate adsorbed at the neutral sites increased, varying from 51% at 4.9 μeq/ml to 68% at 99 μeq/ml. The form of sulfate bonding was apparently governed by the level of the positive charge on the clay surface. Higher positive charge at low and intermediate levels of sulfate saturation resulted in the adsorption of sulfate as a divalent anion by forming a 6-member ring with surface Al. With a decrease in positive charge at higher levels of adsorption, the sulfate ion formed both monodentate and bidentate complexes.

The lacustrine Sucker Creek Formation (Miocene) of eastern Oregon includes unaltered vitric tuffs as well as tuffs altered to the following diagenetic fades: (1) bentonite, (2) interbedded bentonite and opal-CT, (3) K-clinoptilolite, and (4) Ca-clinoptilolite. Bentonite beds contain Fe-rich smectite (8–10 wt. % Fe2O3), quartz, plagioclase, and Ca-clinoptilolite. Opal-CT-rich layers contain inorganic silica (opal-CT), Fe-rich smectite, and minor diatoms. K-clinoptilolite beds typically contain clinoptilolite that can be extremely K-rich (≤7.6 wt. % K2O), opal-CT, smectite, plagioclase, and K-feldspar. This diagenetic facies also includes smectitic tuff and unaltered tuff. Ca-clinoptilolite beds contain Ca-clinoptilolite, quartz, K-feldspar, smectite, and illite.

Based on its chemistry and mineralogy, the bentonite appears to have been derived from dacitic volcanic ash. Chemical considerations and the close spatial relationship between beds of bentonite and opal-CT suggest that the diagenetic alteration of glass to smectite provided silica to the adjacent opal-CT beds. Based on the presence of late-stage Ca-clinoptilolite, alteration appears to have proceeded in a relatively closed chemical system.

Based on the composition of preserved vitric tuff, the zeolitic tuffs appear to be derived from rhyolitic ash, which diagenetically altered in an open hydrologic system and produced vertical zonations in mineralogy. In this model, bentonite horizons at the top of the K-clinoptilolite diagenetic fades formed by reaction of volcanic glass with dilute fluids that had a relatively low (Na+ + K+ + Ca2+)/H+ activity ratio and ${\mathrm{a}}_{{\mathrm{H}}_4{\mathrm{S}\mathrm{i}\mathrm{O}}_4}$, whereas the underlying K-clinoptilolite beds formed from reactions between glass and dilute fluids having a higher (Na+ + K+ + Ca2+)/H+ activity ratio and ${\mathrm{a}}_{{\mathrm{H}}_4{\mathrm{S}\mathrm{i}\mathrm{O}}_4}$. Unaltered vitric ash between these beds may represent zones of higher permeability that inhibited secondary mineral alteration. Ca-clinoptilo-lite-rich beds appear to have undergone alteration similar to K-clinoptilolite-rich beds as well as to have been subjected to later, low-temperature (perhaps 75°–150°C) hydrothermal alteration which enhanced cation exchange in the zeolite and formed quartz from opal-CT.

The purpose of this article is to attempt to discern better the situation of art in contemporary society. To do this we will examine essentially the exterior forces which influence it. These multiple and diverse evolutionary forces are in a certain manner centripetal, and ultimately they modify our concepts of art as such. Without going so far as to state that contemporary society has completely overturned our ideas on this question, signs of change are nevertheless visible which challenge fundamental characteristics up until now attributed to art.

Kuhn's theory of scientific change is founded on the idea that there are minimal defensible grounds for the claim that the history of science is characterized by the cumulative growth of knowledge. According to Kuhn, revolutionary theories in the history of science cannot be perceived as logical and empirical derivations from their predecessors since, quite often, the research methods, theoretical assumptions and the empirical findings of the former are incompatible with the latter. Thus, the analysis of each novel scientific theory must begin with a recognition of the epistemological and ontological independence of that theory's paradigm.

The occurrence of palygorskite in some Tertiary sediments in eastern Saudi Arabia was studied. Mineralogical and chemical analyses were made of samples from two sections several meters thick from the Umm er Radhuma and Dammam Formations of Paleocene and Eocene periods, respectively. Layers of shales were observed within the sections of the dolomitic-calcitic limestone of the Umm er Radhuma Formation and of the dolomitic limestone of the Dammam Formation. After treatment for carbonate removal the shales consisted of more than 95% clay-size particles, most of which were <0.2-μm in size. Palygorskite was the main constituent of some of the shales, with minor amounts of gypsum, soluble salts, and carbonates. The association of gypsum and other salts with palygorskite in the shale suggests that palygorskite formed in closed-basin environments. The presence of palygorskite and the absence of other minerals in the clay fraction of the limestones also suggests that the palygorskite formed under marine conditions.

Scanning, transmission, and analytical electron microscopy studies of shales from the Salton Sea geothermal field revealed that phyllosilicates progress through zones of illite-muscovite (115°−220°C), chlorite (220°−310°C), and biotite (310°C). These phyllosilicates occur principally as discrete, euhedral to subhedral crystals which partly fill pore space. The structural and chemical heterogeneity, which is typical of phyllosilicates in shales subject to diagenesis, is generally absent. Textures and microstructures indicate that the mineral progression involves dissolution of detrital phases, mass transport through interconnecting pore space, and direct crystallization of phyllosilicates from solution.

Phyllosilicate stability relations indicate that either increase in temperature or changing ion concentrations in solutions with depth are capable of explaining the observed mineral zoning. Textural and compositional data suggest that the observed mineral assemblages and the interstitial fluids approach equilibrium relative to the original detrital suites. The alteration process may have occurred in a single, short-lived, episodic hydrothermal event in which the original detrital phases (smectite, etc.) reacted directly to precipitate illite, chlorite, or biotite at different temperatures (depths) without producing intermediate phases.

On principle, there are no language classifications which are right or wrong, but only classifications which are more or less useful or useless. This statement at the beginning of my paper is intended to indicate the teleological perspective in which I want to view the more general problems involved in the classification of African languages. I shall discuss these within a framework which I derive from the four main components of any language classification, namely:

1. 1. the aims and objectives of language classification,

2. 2. the basic units to be classified,

3. 3. the criteria of classification,

4. 4. the models of language classification.

At its birth, a new scientific discipline is baptized with the names of the two parent disciplines, Science X and Science Y. Subsequently, usage tends to shorten this compound name by giving preference to one or the other of the constituting terms so that the new term is less disconcerting and novel. Take biophysics, for example. Is it more closely related to physics than to biology, or the other way round? Today this question seems naive but it did not appear so a scarce thirty years ago, that is, at the beginning of the creative activity of the most, eminent scientists in the field of biophysics: it was then the subject of intense discussion.

Three montmorillonite samples, from Wyoming (particle size <0.2 µm, 4.6 wt. % Fe2O3), Greece (<14 µm, 6.5 wt. % Fe2O3), and Poland (0.5 wt. % Fe2O3, two fractions <2 µm and 2–10 µm) were intercalated with hydroxy-Al species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 wt. % Al2O3 for 0.2 µm in size to 22.6 wt. % for >2 µm. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80°C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 Å. The diffusion of the Al cations therefore limited the cation-exchange process. The addition of NH4+ to the pillaring solution decreased the amount of Al fixed by the clay from 31 (no NH4+ to 26 wt. % (NH4+/Al = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4+ and Al-hydroxy cations for ion-exchange sites forced the Al species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Al exchanged was then reduced. After calcination in air at 700°C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4+ was added, compared with 0.11 ml/g for a NH4+/Al ratio of 10. The Fe content of the clay affected the thermal stability of pillared clays at 800°C: for two samples prepared by competitive ion exchange (NH4+/Al = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe2O3 to 0.08 ml/g for 0.5 wt. % Fe2O3. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150°C, on samples calcined at 500°C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.