bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mg-Smectite Authigenesis in a Marine Evaporative Environment, Salina Ometepec, Baja California
Authors: Hover Victoria C. , Walter Lynn M. , Peacor Donald R. , Martini Anna M. 
Published: August 2006

AbstractFormation of authigenic trioctahedral Mg-rich smectite is common in evaporative lake sediments, but was not described previously in modern marine evaporative environments. This study documents formation of authigenic K-rich, Mg-smectite during very early diagenesis in the dominantly siliciclastic Salina Ometepec (Baja California), a large supratidal evaporative sabkha complex near the mouth of the Colorado River. Here, sediment pore waters are exceptionally Mg2+-rich relative to other marine evaporative environments due to suppressed sulfate reduction which limits production of carbonate alkalinity and, hence, carbonate (particularly dolomite) precipitation. Sediment cores were obtained along a five km transect seaward across the hypersaline mud flat to evaluate how these atypical geochemical conditions would affect the clay mineral compositions.Scanning transmission electron microscopy (STEM) observations show that the smectite from the marine Inlet, near the sediment source, consists of grains of irregular shape that give selected area diffraction (SAED) patterns reflecting dominant turbostratic stacking. Analytical electron microscopy (AEM) analyses indicate that K+ is the dominant interlayer cation; the mean composition is approximately K0.7(Al3.3Fe(III)0.3Mg0.5)(Al0.5Si7.5)O20(OH)4. Such smectite is implied to be detrital in part because it is similar to smectite known to be deposited by the Colorado River.Smectite from the hypersaline mud flat occurs as aggregates of small subhedral pseudohexagonal plate or lath-shaped crystals ≤250 nm in diameter, with thicknesses varying between three and ten layers. The SAED patterns reflect substantial turbostratic stacking, but with a greater frequency of interlayer coherency as compared with detrital smectite. Crystals from greater sediment depths are larger and more nearly euhedral. This smectite is dominantly trioctahedral, with mean composition approximately K0.7(Al0.7Fe(III)0.5Mg4.45)(Al1.2Si6.8)O20(OH)4 (saponitic). This smectite is inferred to be dominantly authigenic in origin.The X-ray diffraction (XRD) and STEM/AEM data collectively imply that detrital aluminous dioctahedral smectite reacts to form authigenic Mg-rich trioctahedral smectite, driven in part by the high Mg2+/ Ca2+ ratio of pore waters. Such early-formed Mg-rich smectite may be the precursor for the trioctahedral mixed-layer smectite, corrensite, and chlorite assemblages found in ancient marine evaporative sequences. These results also add to the accumulating evidence that interlayer K+ in marine smectite is fixed during the earliest stages of marine diagenesis near the sediment water interface.
The Kinetics of the Smectite to Illite Transformation in Cretaceous Bentonites, Cerro Negro, New Mexico
Authors: Elliott W. Crawford , Edenfield Andrea M. , Wampler J. Marion , Matisoff Gerald , Long Philip E. 
Published: August 2006

AbstractThe thermal effects, as well as the survivability and origins of microorganisms in Cretaceous rocks, are evaluated from the timing and extent of the smectite to illite transformation in Cretaceous bentonites collected from cores outside the thermal aureole of the Pliocene Cerro Negro volcanic neck. Overall, randomly ordered mixed-layered illite-smectite (I-S) is the predominant clay mineral in these bentonites, and the K-Ar ages of I-S range from 36 to 48 Ma (21 analyses, two additional analyses were outside this range). Increased temperature from burial is thought to be the primary factor forming I-S in these bentonites. Kinetic model calculations of the smectite to illite transformation are also consistent with I-S formed by burial without any appreciable thermal effects due to the emplacement of Cerro Negro. In a core angled toward Cerro Negro, the percentages of illite layers in I-S from the bentonite closest to Cerro Negro are slightly higher (32-37%) than in most other bentonites in this study. The K-Ar ages of the closest I-S are slightly younger as a group (38-43 Ma; Average = 41 Ma; N = 4) than those of I-S further from Cerro Negro in the same core (41-48 Ma; Average = 44 Ma; N = 6). A small amount of illite in this I-S may have formed by heat from the emplacement of Cerro Negro, but most illite formed from burial. Vitrinite reflectance, however, appears to record the effects of heating from Cerro Negro better than I-S. Tentatively, the temperature of this heat pulse, based on vitrinite data alone, ranged from 100 to 125°C and this is most evident in the CNAR core. The upper temperature, 125°C, approximates the sterilization temperatures for most microorganisms, and these temperatures probably reduced a significant portion of the microbial population. Thermophiles may have survived the increased temperatures from the combined effects of burial and the intrusion of Cerro Negro.
New Techniques for Studying the Intercalation of Kaolinites from Georgia with Formamide
Authors: Frost Ray L. , Lack Daniel A. , Paroz Gina N. , Tran Thu Ha T. 
Published: August 2006

AbstractA new technique utilizing Raman microscopy and Fourier transform infrared (FTIR) microsacopy is described. This technique uses thin films of oriented clay aggregates on glass slides suitable also for X-ray diffraction (XRD). Raman microscopy proved the most useful technique providing both better resolution of the OH-stretching bands and greater spectral resolution. Kaolinites from Washington County, Georgia, with varying defect structures involving layer stacking were intercalated with formamide and additional Raman bands were observed at 3610 and 3627 cm−1. A concomitant decrease in the inner-surface OH band intensities at 3695 and 3685 cm−1 occurred. These bands are attributed to the inner-surface OH hydrogen bonded to the formamide molecule through the C=O group. The 3627 cm−1 band is sharp with a half width of 7.5 cm−1 and comprises 11% of the total normalized band area. When two additional OH bands are observed at 3610 and 3627 cm−1 two C=O bands at 1674 and 1658 cm−1 are observed also. The two additional Raman inner-surface OH bands were not observed in the IR spectra. However, a band of low intensity was observed at 3590 cm−1. Models for the intercalation of formamide in kaolinites are proposed.
Interaction of Synthetic Sulphate “Green Rust” with Phosphate and the Crystallization of Vivianite
Authors: Hansen Hans Christian Bruun , Poulsen Inge Fiil 
Published: August 2006

AbstractBecause layered Fe(II)Fe(III)-hydroxides (Green rusts, GRs) are anion exchangers, they represent potential orthophosphate sorbents in anoxic soils and sediments. To evaluate this possibility, two types of experiments with synthetic sulphate-interlayered GRs (GRSO4 = Fe2+4Fe3+2(OH)12SO4 ×H2O) were studied. First, sorption of phosphate in GRSO4 was followed by reacting suspensions of pure GRSO4 synthesized by oxidation of Fe(II) with an excess of Na2HPO4 (pH 9.3). Second the possible incorporation of phosphate in GR during formation by Fe(II)-induced reductive dissolution of phosphate-containing ferrihydrites was examined in systems containing an excess of Fe(II) (pH 7). With excess phosphate in solution, GRSO4 initially sorbed phosphate in the interlayer producing a basal layer spacing of 1.04 nm, but only ~50% of the interlayer sulphate was exchanged with phosphate. This GR slowly transformed to vivianite within months. In the Fe(II)-rich systems, reaction with synthetic ferrihydrites produced GRSO4 similar to that produced by air oxidation. Reaction of Fe(II) with phosphate-containing ferrihydrites initially produced amorphous greenish phosphate containing precipitates which, after 3–4 h, crystallized to GRSO4 and vivianite. In these solutions, stable phosphate-free GRSO4 can form since precipitation of vivianite produced low phosphate activity. Consequently, in both systems GR or amorphous greenish precipitates act as reactive intermediates, but vivianite is the stable end-product limiting phosphate concentration in solution. It is also inferred that Fe(OH)2 is an unlikely phosphate sorbent in mixed Fe(II)-Fe(III) systems because GR phases are more stable (less soluble) than Fe(OH)2.
Occurrence of Clinoptilolite and Mordenite in Tertiary Calc-Alkaline Pyroclastites from Sardinia (Italy)
Authors: Ghiara Maria R. , Petti Carmela , Franco Enrico , Lonis Roberto , Luxoro Santina , Gnazzo Lucio 
Published: August 2006

AbstractClinoptilolite and mordenite occur as diagenetic products of medium-grained, moderately welded and poorly sorted pyroclastic flows belonging to the Tertiary calc-alkaline volcanism of Sardinia. Both clinoptilolite and mordenite occur within pyroclastic flows of the same stratigraphic unit. Mordenite frequently occurs in the late volcanic sequences from Anglona area (northern Sardinia). Textural features indicate that zeolites are products of glass alteration. Thin sections show either complete alteration of glassy shards by clinoptilolite and mordenite or unaltered shards with clinoptilolite or mordenite confined to the cineritic matrix. During the zeolitization process, interacting fluids were important in the mobilization and distribution of alkali elements. The compositional variations of clinoptilolite and mordenite within a single sample showed trends that suggest steps in a continuous process probably evolving towards equilibrium conditions.
Distinguishing Between Surface and Bulk Dehydration-Dehydroxylation Reactions in Synthetic Goethites by High-Resolution Thermogravimetric Analysis
Authors: Ford Robert G. , Bertsch Paul M. 
Published: August 2006

AbstractSynthetic goethites studied by high-resolution thermogravimetry (HRTGA) show variability in surface characteristics and structural stability as a function of aging conditions. Goethites were synthesized at either pH 6 or 11, at temperatures of 40 or 70°C, and in the presence or absence of sorbed Mn or Pb. Data from HRTGA analysis revealed at least four distinct weight-loss events near goethite dehydroxylation that relate to 1) three events involving the evolution of water associated with surface Fe-O functional groups and 2) bulk dehydroxylation of goethite during transformation to hematite. The relative mass of evolved surface and bulk structural water was related to the predominant particle morphology as determined by transmission electron microscopy (TEM). Differentiation of surface and bulk decomposition reactions allowed the identification of bulk structural dehydroxylation. Goethite crystallin-ity, estimated by the bulk dehydroxylation temperature, appeared to depend on the kinetics of crystallization. This trend was most evident for systems aged at pH 11 and 40°C. Greater concentrations of coprecipitated Mn or Pb dramatically improved goethite crystallinity as indicated by higher dehydroxylation temperatures and smaller widths of the (110) Bragg reflection. Comparison of bulk dehydroxylation temperatures for these samples to other preparations suggests that structural defects predominated over the effects of particle size and Mn/Pb substitution in determining goethite thermal stability. A conceptual model is proposed to account for the disparate dehydroxylation profiles displayed by goethites of varying crystallinity.
A New Approach to Compositional Limits for Sepiolite and Palygorskite
Authors: Galan Emilio , Carretero Ma Isabel 
Published: August 2006

AbstractMost bulk chemical analyses of sepiolite and palygorskite available in the literature are erroneous because samples analyzed are admixtures of minerals that are difficult to separate or identify by other techniques. Some chemical analyses performed on selected individual particles by energy dispersive X-ray analysis (EDX) are also influenced by the same problem. Chemical analyses are summarized for sepiolite and palygorskite reported in the literature (bulk and EDX analyses). The analyses are evaluated by comparison to three sepiolite and three palygorskite pure samples analyzed by EDX techniques. Results indicate that sepiolite is a true trioctahedral mineral, very pure (near end-member) with negligible structural substitution and with eight octahedral positions filled with magnesium, close to the theoretical formula Mg8Si12O30(OH)4(OH2)4(H2O)8. Palygorskite is intermediate between di- and trioctahedral phyllosilicates. The octahedral sheet contains mainly Mg, Al, and Fe with a R2/R3 ratio close to 1, and with four of the five structural positions occupied. The theoretical formula is close to (Mg2R23+?1)(Si8-xAlx)O20(OH)3(OH2)4·R2+x/2(H2O)4, where x = 0–0.5. Sepiolite and palygorskite are thus more compositionally limited than previously reported.
A Synthetic Na-Rich Mica: Synthesis and Characterization by 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
Authors: Komarneni Sridhar , Pidugu Rajyalakshmi , Hoffbauer W. , Schneider Hartmut 
Published: August 2006

AbstractA swelling mica, Na2Mg3(Al2Si2)O10F2·xH2O, (hereafter “Na-4 mica”) was synthesized from metakaolinite + MgO and Mg aluminosilicate gels at different temperatures and durations using NaF flux. The various samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and 27A1 and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The results showed that phase-pure Na-4 mica was obtained from metakaolinite which serves as a cost-effective aluminosilicate source. 27Al MAS NMR spectra showed that all or nearly all Al is in tetrahedral coordination whereas 29Si MAS NMR spectra showed that the nearest neighbor environment of Si is mainly Si(3Al), as expected based on the Si:Al ratio.
The Effect of Dry Grinding on Antigorite from Mulhacen, Spain
Authors: Drief A. , Nieto F. 
Published: August 2006

AbstractAlteration of the crystal structure of Mulhacén antigorite caused by dry, vibration grinding was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analyses (TG), grain-size distribution, and transmission and analytical electron microscopy (TEM, AEM). Grinding for 1 min reduces particles to a size ideal for IR and TG. With prolonged grinding, XRD and electron diffraction patterns showed that the crystal structure was affected mainly along the c axis, causing a partial loss of crystallinity. TG analyses revealed that vibration grinding modified mineral dehydration, accelerating the dehydroxylation process and transforming the structural OH to adsorbed water in the resulting matrix. IR spectra and AEM showed that grinding affected the tetrahedral sheet to a lesser extent than the octahedral sheet. Partial release of Mg by preferential destruction of the octahedral sheet after 10 min grinding produced an increase in the Si/Mg ratio in semi-crystalline particles, whereas the amorphous material product after 120 min showed the same composition as the initial antigorite. TEM and grain-size distribution results revealed that grinding led to a general decrease in particle size at the beginning of the experiment followed by the agglomeration of ultrafine particles as grinding proceeded.
Ambient-Temperature Synthesis, Evolution, and Characterization of Cobalt-Aluminum Hydrotalcite-Like Solids
Authors: Thompson Hillary A. , Parks George A. , Brown Gordon E. 
Published: August 2006

AbstractDouble hydroxide solids precipitated homogeneously from three laboratory-synthesized aqueous solutions that simulated mildly contaminated surface or groundwater. Over a limited pH range, precipitates formed rapidly from dissolved ions, and more slowly by incorporating ions dissolving from other solids, including highly soluble aluminous solids. The precipitates were characterized by size and shape via transmission electron microscopy (TEM), by composition via inductively coupled plasma-mass spectrometry (ICP-MS) of mother solutions and analytical electron microscopy (AEM) of precipitates, and by structure via powder X-ray diffraction (XRD), TEM, and extended X-ray absorption fine structure (EXAFS) spectroscopy. They were identified as nanocrystalline cobalt hydrotalcite (CoHT) of the form [Co(II)1-xAl(III)x(OH)2]x+(An−x/n)·mH2O, with x = 0.17–0.25, A = CO32−, NO3−, or H3SiO4−n = anion charge and m undetermined. Complete solid solution may exist at the macroscopic level for the range of stoichiometrics reported, but clustering of Co atoms within hydroxide layers indicates a degree of immiscibility at the molecular scale. Composition evolved toward the Co-rich endmember with time for at least one precipitate. The small layer charge in the x = 0.17 precipitate caused anionic interlayers to be incomplete, producing interstratification of hydrotalcite and brucite-like layers. Solubility products estimated from solution measurements for the observed final CoHT stoichiometries suggest that CoHT is less soluble than the inactive forms of Co(OH)2 and CoCO3 near neutral pH. Low solubility and rapid formation suggest that CoHT solids may be important sinks for Co in contact with near neutral pH waters. Because hydrotalcite can incorporate a range of transition metals, precipitation of hydrotalcite may be similarly effective for removing other trace metals from natural waters.
Partial Stabilization of Fe(II) in Reduced Ferruginous Smectite by Li Fixation
Authors: Komadel Peter , Madejová Jana , Stucki Joseph W. 
Published: August 2006

AbstractPartial stabilization of Fe(II) in chemically reduced smectite, which normally readily undergoes reoxidation in air, was achieved. The purpose of this study was to determine if Fe(II) can be stabilized in reduced smectites by Li fixation upon heating. More than 80% of total Fe in ferruginous smectite SWa-1 was reduced to Fe(II) using the citrate-bicarbonate-dithionite (CBD) method while purging the clay dispersion with N2. The reduced smectite was Li-saturated, washed free of excess ions, freeze-dried, and heated in N2 atmosphere at 260°C for 24 h to produce Li-fixation. This treatment caused partial stabilization of Fe(II) in the clay structure. Chemical analysis, Mössbauer spectroscopy, and Fourier transform infrared (FTIR) spectroscopy proved that <20% of total Fe was Fe(II) after reoxidation with oxygen in a water dispersion, a treatment which causes complete reoxidation of Fe(II) in reduced Na-smectites. Decomposition of the OH-stretching band evident in the IR spectra indicated migration of Li into the vacant octahedra. Some of the OH groups in the reoxidized smectite were found in local trioctahedral configurations, associated with the AlFe(II)Li or Fe(III)Fe(II)Li groupings of central atoms in the octahedral sheet.
Effect of Acid Activation on the De-Tert-Butylation Activity of Some Jordanian Clays
Authors: Mahmoud Sabri , Saleh Sadiq 
Published: August 2006

AbstractJordanian natural kaolin and bentonite show good catalytic activity towards debutylating 2-tert-butylphenol, and varying debutylation vs. isomerization selectivity after acid activation. The resulting catalytic activity of these samples is dependent on the acid employed for activation; the samples treated with acetic acid showed relatively low conversions, whereas those treated with hydrochloric or phosphoric acid were found to be very active. Treatments with strong acids such as HCl have various effects on the activity of the samples depending on the concentration of the acid. For example, treatment with 1 M HCl gives the highest activity, whereas a treatment using 12 M HCl produced the lowest activity. The debutylation selectivity of the acid-activated samples is affected by the acid type and/or concentration. This selectivity ranges from 20 to 60%, whereas that of water-treated samples is between 46–82%.
Preferred Orientation of Phyllosilicates in Gulf Coast Mudstones and Relation to the Smectite-Illite Transition
Authors: Ho Nei-Che , Peacor Donald R. , van der Pluijm Ben A. 
Published: August 2006

AbstractDevelopment of preferred orientations of illite-smectite (I-S) has been studied using X-ray diffraction (XRD) texture goniometry to produce pole figures for clay minerals of a suite of 16 mudstone samples from a core from the Gulf Coast. Samples represent a compaction-loading environment in which the smectite-to-illite (S-I) transition occurs. In five shallow, pre-transition samples, there is no significant preferred orientation for smectite-rich I-S. Development of preferred orientation of I-S, although weak, was first detected at depths slightly less than that of the S-I transition. The degree of preferred orientation, which is always bedding-parallel, increases rather abruptly, but continuously, over a narrow interval corresponding to the onset of the S-I transition, then continues to strengthen only slightly with increasing depth. The degree of post-transition preferred orientation is also dependent on lithology, where the preferred orientation is less well-defined for quartz-rich samples.Previously obtained transmission electron microscope (TEM) data define textures consistent with the change in orientation over many crystallites. The smectite in pre-transition rocks consists largely of anastomosing, “wavy” layers with variable orientation and whose mean orientation is parallel to bedding, but which deviate continuously from that orientation. This results in broad, poorly defined peaks in pole figures. Post-transition illite, by contrast, consists of thin, straight packets, with most individual crystallites being parallel or nearly parallel to bedding. This results in pole figures with sharply defined maxima. By analogy with development of slaty cleavage in response to tectonic stress during metamorphism, the S-I transition is marked by dissolution of smectite and neocrystallization of illite or I-S locally within the continuous “megacrystals” of smectite. The transition is inferred to have some component of mechanical rotation of coherent illite crystals within a pliant matrix of smectite. The data suggest that change in orientation and coalescence of clay packets plays an important role in the formation of the hydraulic seal required for overpressure generation.
Pedogenic Formation of Kaolinite-Smectite Mixed Layers in a Soil Toposequence Developed from Basaltic Parent Material in Sardinia (Italy)
Authors: Righi Dominique , Terribile Fabio , Petit Sabine 
Published: August 2006

AbstractFormation of kaolinite-smectite (K-S) mixed layers in a soil toposequence developed from basaltic parent material was examined. The soil formed in a temperate climate with alternating dry and wet seasons in Sardinia (Italy). Chemical composition and charge characteristics of the smectite component in the K-S mixed layers were analyzed to help determine a mechanism for formation. Soils were sampled at the top, intermediate, and base of a steep (35%) slope. As indicated by X-ray diffraction data, the fine clay fraction (>0.1 μm) in the soils is dominated by K-S with a decreasing proportion of kaolinite from the top (70%) to the base (30%). Rapid internal drainage induced by the slope is probably the major factor responsible for the formation of K-S. Chemical composition and charge characteristics of the smectite component in the K-S were analyzed by X-ray diffraction (intercalation with alkylammonium ions), cation exchanged capacity (CEC) and surface area measurements, and infrared spectroscopy. Results indicate that the smectite component is nearly identical over the soil toposequence. The smectite component is the same with respect to charge magnitude and chemical composition, independent of the proportion of kaolinite and smectite components. This suggests the pedogenic formation of K-S by transformation of smectite through dissolution of some smectite layers and subsequent crystallization of kaolinite between the layers of the remaining smectite crystallites.