Mixed-layer compounds from the tetradymite group, in the range Bi2Te3-Bi8Te3, were studied by HRTEM. The formula S′(Bi2kX3)·L′[Bi2(k+1)X3] (X = chalcogen; S′, L′ = number of short and long modules, respectively) was introduced as a working model. Diffraction patterns show that all phases are N-fold (N = layers in the stacking sequence) superstructures of a rhombohedral subcell with c/3 = d1 ~ 0.2 nm. The patterns, with two brightest reflections about the middle of d1*, are described by monotonic decrease of two modulations with increase in Bi: (1) q = γcsub* (q ~ homoatomic interval; γ = 1.8-1.64 for analytical range; csub ~ 3d1), based on displacive modulation between chalcogen and Bi atoms; and (2) qF = γFcsub*; qF = (i/N)d1* = idN*, i = S′ + L′, relating changes in module size and number to displacements in a basic substructure.
Slurries formed by the neutralization of tailings from acid-extracted ground rock contain sulphates. As the slurries dry out, sulphate precipitates, and the solid sulphates present dehydrate. The dehydration of pure calcium and magnesium sulphates was determined over a range of relative humidities at 20°C and after oven-drying. The results were used to help determine the amounts and forms of sulphates present in two samples of tailings after air-drying and oven-drying. One sample had been neutralized with lime and the other with calcined magnesite. The forms were similar to those of the pure salts under the same drying conditions. Expressions were then developed for calculating bulk properties of tailings from experimental measurements. The properties were the pore and specific volumes of slurries, derived from gravimetric water content, and the density of solids in oven-dried tailings from water displacement. Using the two samples of tailings, it was shown that values of solids density agreed with values calculated in the usual way from measurements on sulphate-free samples. It was also calculated that the correction for solids density would be negligible if sodium chloride were the only salt present. Les boues liquides obtenues par neutralisation des résidus par extraction d'acide des roches moulues contiennent des sulfates. Lorsque les boues liquides sèchent, le sulfate précipite et les sulfates solides présents se déshydratent. La déshydratation des sulfates purs de calcium et de magnésium a été mesurée pour différentes humidités relatives, sous une température de 20°C ou après passage à l'étuve. Le résultats ont été utilisés pour déterminer la quantité et la forme des sulfates présents dans deux échantillons de résidu, après séchage à l'air et séchage à l'étuve. L'un des échantillons a été neutralisé par de la chaux, l'autre par de la magnésite calcinée. Les formes sont similaires à celles des sels purs pour les mêmes conditions de séchage. Des relations ont alors été proposées pour évaluer les propriétés des résidus à partir de mesures expérimentales. Ces propriétés sont les volumes poreux et spécifiques des boues et la densité des solides dans les résidus sèches à l'étuve. Les volumes ont été évalués à partir de la teneur en eau gravimé-trique, la densité à partir d'un déplacement d'eau. Pour les deux échantillons de résidu, il apparaît que la densité des solides évaluée est en bon accord avec les valeurs calculées par les méthodes habituelles de mesure sur des échantillons sans sulfate. Il apparaît également que les corrections de densité des solides sont négligeables si le chlorure de sodium est le seul sel présent.
We show that Hnrr,lr is useful for distinguishing the one-layer polytypes of chlorite and for characterizing layer stacking sequences. HRTEM images were computed for all onelayer chlorite polytypes. These computations how that the features in Hnreu images can be used to determine the projected shift vectors across the T layers and B sheets. These vectors can, in turn, be used to distinguish among the several possible chlorite polytypes. Five distinct projections result from viewing all possible one-layer chlorite polytypes down their (100) or (l l0) zone axes (assigning [T00] parallel to the talc-stagger direction). Complete specification of polytypes requires either HnrEu combined with X-ray diffraction analysis or HRTEM images from more than one major zone of the same crystal. A clinochlore sample from West Chester, Pennsylvania, was used as an example of the use of HRTEM to study chlorite polytypism. Single-crystal X-ray analysis showed the sample to be an ordered one-layer IIb-2 polytype. Electron diffraction patterns from a much smaller volume of crystal than was used for the X-ray measurements how streaking parallel to c* in the k I 3n reciprocal lattice rows, indicating b/3 shifts of the chlorite layers. High-resolution imaging of this crystal i l lustrates the regular alternation of the T layers and B sheets. In addition, semi-random stacking sequences are the dominant type of disorder whereas layer rotations occur less frequently.
The origin of the variety of body colors exhibited by South Sea Pearls is in part due to a newly recognized structure of the nacre, the edge-band structure, which gives rise to interference colors characteristic of its width. With the pearl oyster, Pinctada maxima, the colors include a range of silver tones, creams, yellows, and gold in various degrees of color saturation. We establish here that the primary body color of P. maxima pearls arises from the interference of light within the binding regions of the aragonite tiles. The tile faces terminate in a fi ssured nano-composite structure containing organic matrix within the margin of the aragonite tiles. This edge-band structure gives rise to an optical film formed of organic matrix in aragonite. The TEM images show that the edge-band structure width increases progressively from 74(4) nm in a silver pearl, to 80(4) nm in a cream pearl, and to 90(4) nm in a gold pearl. These colors are the first-order Newton's colors, which, when mixed with the specular reflection of the nacre and modified by any pigmentation present, give rise to the body color of pearls. The non-metallic whiter pearls more commonly seen can be accounted for by disorder of this structure leading to unsaturation of the color.
Before regulation, the White Nile contributed 83% of the low water flow to the main Nile and was responsible for maintaining the Nile as a perennial river during times of drought in Ethiopia. Two key unresolved questions relating to the White Nile are: (a) When did the White Nile first join the main Nile? (b) What type of sediment did the White Nile contribute to the main Nile? The answer to the first question has important implications for our understanding of hydro–climatic and tectonic events in the Ugandan Lake Plateau. The answer to the second question is essential for correctly interpreting the sedimentary record preserved in the Nile deep sea fan in the eastern Mediterranean. Our work has shown for the first time that the White Nile has been transporting smectite–rich sediments from the time of its probable inception over 240 ka ago and possibly since about 400 ka. Our analysis of the heavy mineral assemblages in White Nile alluvial sediments provides strong support for a source in the Lake Plateau region of Uganda. The White Nile was flowing from Uganda by at least 240 ka and very likely from about 400 ka.
Abstract Meurigite is a new hydrated potassium iron phosphate related to kidwellite and with structural similarities to other late-stage fibrous ferric phosphate species. It has been found at four localities so far — the Santa Rita mine, New Mexico, U.S.A.; the Hagendorf-Sud pegmatite in Bavaria, Germany; granite pegmatite veins at Wycheproof, Victoria, Australia; and at the Gold Quarry Mine, Nevada, U.S.A. The Santa Rita mine is the designated type locality. Meurigite occurs as tabular, elongated crystals forming spherical and hemispherical clusters and drusy coatings. The colour ranges from creamy white to pale yellow and yellowish brown. At the type locality, the hemispheres may reach 2 mm across, but the maximum diameter reached in the other occurrences is usually less than 0.5 mm. A wide variety of secondary phosphate minerals accompanies meurigite at each locality, with dufrenite, cyrilovite, beraunite, rockbridgeite and leucophosphite amongst the most common. Vanadates and uranates occur with meurigite at the Gold Quarry mine. Electron microprobe analysis and separate determination of H 2 O and CO 2 on meurigite from the type locality gave a composition for which several empirical formulae could be calculated. The preferred formula, obtained on the basis of 35 oxygen atoms, is which simplies Qualitative analyses only were obtained for meurigite from the other localities, due to the softness and openness of the aggregates. Because of the fibrous nature of meurigite, it was not possible to determine the crystal structure, hence the exact stoichiometry remains uncertain. The lustre of meurigite varies from vitreous to waxy for the Santa Rita mine mineral, to silky for the more open sprays and internal surfaces elsewhere. The streak is very pale yellow to cream and the estimated Mohs hardness is about 3. Cleavage is perfect on {001} and fragments from the type material have a mean specific gravity of 2.96. The strongest lines in the X-ray powder pattern for the type material are ( d obs , I obs , hkl ) 3.216(100)404; 4.84(90)111; 3.116(80)205; 4.32(70)112; 9.41(60)201; 3.470(60)800. The X-ray data were indexed on the basis of a monoclinic unit cell determined from electron diffraction patterns. The cell parameters, refined by least squares methods, are a = 29.52(4), b = 5.249(6), c = 18.26(1) Å, β = 109.27(7)°, V = 2672(3) Å 3 , and Z = 4. The calculated density is 2.89 gcm −3 . The space group is either C 2, Cm or C 2/ m . X-ray powder data for meurigite are closely similar to those for kidwellite and phosphofibrite, but meurigite appears to be characterised by a strong 14 Å reflection. The relationship between these three minerals remains uncertain in the absence of structural data. On the available evidence, meurigite and kidwellite are not the respective K and Na-endmembers of a solid solution series. The meurigite cell parameters suggest it belongs to a structural family of fibrous ferric phosphates, such as rockbridgeite, dufrenite and beraunite, which have a discrete 5 Å fibre axis. Meurigite occurs in widely varying environments, its formation probably favoured by late-stage solutions rich in K rather than Na.
We employed x‐ray computed microtomography (X‐ray CT) to observe differences in moisture around fertilizer P granules (monoammonium phosphate, MAP) versus injection zones of fluid P fertilizer (technical grade monoammonium phosphate, TG MAP) in a calcareous soil over time. X‐ray CT allows nondestructive visualization of small columns containing soils and fertilizers. We were able to visualize the increase in density around the highly hygroscopic fertilizer granule over time. It appeared that both water flow toward the granule and precipitation of P could be responsible for the development of about 1 mm thick high density zone immediately adjacent to the granule. The mass flow of water toward the granule may have slowed or restricted the diffusion of fertilizer P from the granule, thus increasing the chances for P fixation through precipitation reactions. Also, the granule became less dense with time indicating the progress of granule dissolution. In contrast, injection of fluid fertilizer (TG‐MAP) in soil did not result in moisture changes over time as evidenced by a lack of X‐ray CT detectable density differences in the soil column. These data support previous findings that, when P is supplied in granular form, P diffusion and isotopic lability in calcareous soils are reduced compared with equivalent liquid fertilizer formulations, probably due to precipitation reactions induced by osmotically induced flow of soil moisture into the fertilizer granule.
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