Interstratified Illite Smectite Research Articles

Transmission Electron Microscopy Study of Smectite Illitization During Hydrothermal Alteration of a Rhyolitic Hyaloclastite From Ponza, Italy

AbstractDioctahedral phyllosilicates from an altered rhyolitic hyaloclastite located at Ponza Island, Italy, were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The samples are from a sequence previously characterized by X-ray diffraction (XRD) methods, indicating that a complete range of illitization accompanies alteration. Backscattered electron (BSE) images, obtained from ion-milled samples, show that samples partly retain the original textures since clay minerals pseudomorph lapilli fragments and preserve vesicular texture. The lowest-grade sample studied contains obsidian clasts partially replaced by smectite. As the alteration grade increases, illitization proceeds with formation of interstratified illite-smectite (I-S), zeolites, illitic phases, feldspars and quartz. The most altered sample contains illite, mica and quartz. Lattice-fringe images show that following the formation of smectite, illitization takes place through the formation of (R=1) I-S, highly illitic I-S and illite with mica; (R=1) I-S is the only ordered interstratified I-S. The BSE and TEM images of Ponza samples show irregular cavities filled with euhedral dioctahedral clay minerals and the zeolite mordenite, providing direct evidence for neocrystallization from a fluid. Chemical compositions by analytical electron microscopy (AEM) support the sequence described. Selected area electron diffraction (SAED) patterns indicate the predominance of 1 Md polytypism both in I-S and illitic phases, and the coexistence in the more altered samples of 1Md illite and a 2-layer mica polytype (probably 2M1), without the intermediate 1M polytype generally assumed to exist in prograde sequences. Previous XRD studies indicated progressive change from cis-vacant, turbostratically stacked smectite, to interstratified cis- and trans-vacant, 1Md I-S, to trans-vacant, 1M illite, and then to 2M1 illite in Ponza Island samples. We observed a clear correlation between the chemical compositions as determined by AEM and the proportion of cis-vacant determined by XRD, suggesting that the octahedral cation distributions change in the studied samples with increasing degree of illitization.

Æolian dust contributions to soil of the Namoi Valley, northern NSW, Australia

Æolian processes have been regarded as having little relevance to pedogenesis in the subhumid regions of eastern Australia, due perhaps to a perceived paucity of clear evidence of dust deposition and to difficulties of measuring an æolian dust component within soils. Contrary to earlier opinions, an æolian soil component may occur in eastern Australia, as appreciable amounts of dust are deposited annually. We report dust deposition rates and some dust characteristics at Gunnedah, and measured granulometric, mineralogical and geochemical attributes of four soil profiles found in different physiographic areas of the Namoi Valley. Estimates of dust deposition rates indicate that a deposit at least 20 cm thick could have formed over the last 13,000 years. The soil profile which most clearly indicates the presence of dust overlies basalt at Bald Hill. Here, the topsoil contains a conspicuous population of particles with a modal diameter of 40–50 μm and has been enriched in Si by the addition of quartz, which cannot have originated from the basalt or from colluvial or alluvial processes. A clayey floodplain soil profile (Boonawa) also contained a large dust-particle population and also illite and moderate concentrations of K of possible æolian origin. Two sandy profiles at Round Swamp displayed the same conspicuous dust-particle populations, and one exhibited an interstratified illite–smectite component, suggesting dust additions. Local æolian processes were also indicated by the well-sorted, coarse sand-sized particles of the Round Swamp East profile, located on a low lunette adjacent to the swamp. These fine-grained, quartz-rich, æolian dust deposits differ considerably from the benchmark Australian æolian dust mantles, which form the clay-aggregated, calcareous parna soils of southern New South Wales.

A MS, SEM-EDX and XRD study of Ti or Cu-doped zinc ferrites as regenerable sorbents for hot coal gas desulfurization

The minerals in a range of Colombian coal samples, selected to represent the principal coal-mining regions, have been investigated using low-temperature ashing and quantitative X-ray diffraction techniques, and the results compared to information from chemical analysis and Mössbauer spectroscopy studies. Kaolinite, illite, interstratified illite–smectite and quartz are the dominant mineral matter components in almost all of the coal samples, with small but significant proportions of pyrite (up to around 15% of the mineral matter) being present in around half of the samples studied. Other minerals present in particular samples include chlorite, muscovite, paragonite, ankerite, dolomite, calcite and siderite, along with phosphate minerals apatite and goyazite. Jarosite and coquimbite are also noted in some of the pyrite-bearing coals, probably representing oxidation products of the pyrite developed with exposure or storage. Bassanite is present in the low-temperature ash of some coals, and in one sample occurs along with significant concentrations of hexahydrite, alunogen, tschermigite and paraluminite, all of which were probably derived from interaction of inorganic elements in the organic matter with organic sulphur during maceral oxidation.Quantitative analysis of the minerals in the low-temperature ash of the coal samples using Rietveld-based X-ray diffraction techniques provides results that are consistent, at least for the most abundant elements, with the chemical composition of the coal ash as determined by standard analysis procedures. The evaluation of mineral-rich concentrates by Mössbauer spectroscopy also provides results consistent with the XRD data, especially as regards pyrite and some of the sulphate components. Optical microscopy indicates that much of the pyrite, and in some cases also the carbonates, occurs as anhedral crystals, finely disseminated in the maceral components, as aggregates of crystals (including pyrite framboids), as fine-grained crystals replacing liptinite, and as fracture fillings. Some sub-angular to rounded quartz grains are also present, possibly of detrital origin, but most other minerals, including the clay minerals, occur mainly as aggregates of intimately admixed mineral and maceral constituents.

Diagenesis of Dioctahedral and Trioctahedral Smectites from Alternating Beds in Miocene to Pleistocene Rocks of the Niigata Basin, Japan

AbstractClay mineral diagenesis in the Niigata basin is documented by mineralogical and chemical analysis of clay minerals from cuttings from the Shinkumoide SK-1D (SSK-1D) well which is characterized by alternating beds containing dioctahedral and trioctahedral smectite minerals with increasing depth. Dioctahedral smectite shows a progressive increase in illite interstratification with increasing depth. The transition of dioctahedral smectite to interstratified illite-smectite (I-S) is supported chemically by an increase in K and Al and a decrease in Si with increasing depth. In contrast, trioctahedral smectite (saponite) reacts to form a 1:1 interstratified chlorite-smectite (C-S) with increasing burial depth and temperature. Considering the geology and the occurrence of smectite, the SSK-1D smectites probably altered diagenetically from two different parent materials: dioctahedral smectite is derived from clastic sediments and transforms to interstratified illite-smectite, whereas trioctahedral smectite is derived from andesitic pyroclastic rocks and transforms to interstratified chlorite-smectite.The C-S occurs at the same depth of ~3200 m as the conversion of randomly interstratified (R = 0) I-S to (R = 1) I-S. Furthermore, the depth is compatible with a Tmax temperature of 430-435°C, which indicates the starting temperature for oil generation from organic matter. The temperature of the conversion of (R = 0) I-S to (R = 1) I-S and the start of corrensite formation is estimated at 110-120°C based on the time-temperature model suggested by others. The clay-mineral diagenesis in the SSK-1D further suggests that I-S and C-S can act as geothermometers in clastic and pyroclastic sediments provided that the effect of time is considered.

Relationships between clay mineralogy, hydrothermal metamorphism, and topography in a Western Cascades watershed, Oregon, USA

This study investigates variation in clay mineralogy and its relation to hydrothermal metamorphism, hillslope processes, and topography in the western Cascade Mountains. The study area is the drainage basin of Dorena Lake, a medium-sized (686 km 2) watershed located near Cottage Grove, OR. The Bohemia Mining District is on the southeastern rim of the watershed in a hydrothermally metamorphosed region associated with a set of granodiorite plutons. To characterize large-scale patterns of clay mineral distribution within the watershed, suspended sediments were collected from 43 stream locations. Samples of several metamorphosed and unaffected volcanic and volcaniclastic rocks were collected to help clarify metamorphic reaction processes. One active earthflow was also sampled. X-ray diffraction methods were used to determine the mineralogy of the clay-sized (<2 μm) fraction of the samples. Clay mineralogy varies systematically across the watershed, and the three major stream tributaries carry sediment with distinct mineralogical signatures. Discrete minerals include kaolinite, smectite, chlorite, and illite. Interstratified kaolinite–smectite and chlorite-vermiculite (CV) are also present. The active earthflow and unmetamorphosed rock samples primarily contain smectite. In contrast, metamorphosed rock samples are composed of some combination of illite, interstratified illite–smectite, CV, and chlorite. Examination of clay mineral distribution reveals the effects of hydrothermal metamorphism in the mining district on clay mineralogy, hillslope processes, and landscape development. Compared with most of the watershed, the mining district has steeper slopes and higher elevations and lacks smectite almost entirely. Analyses of metamorphosed bedrock units indicate that smectite originally present in the rocks was converted to nonexpandable clay minerals during metamorphism. Induration of bedrock and loss of expandable clays resulted in thin soils and steep topography. Debris slides and flows are the dominant mass movement processes in this area; earthflows are noticeably absent, probably because thick, smectitic soils are lacking. Elsewhere in the watershed where smectite is abundant, slopes are more gentle; and both shallow and deep-seated mass movements are common. The clay mineralogy of bedrock and soils is thus integrally tied to the hillslope processes operating within the watershed and therefore affects the geomorphology of the landscape. High-relief, hydrothermally metamorphosed volcanic centers surrounded by weaker rocks in adjacent lowlands are common features in the western Cascade Mountains. These massifs were likely formed by differential erosion processes similar to those operating in the Dorena Lake watershed.

Reaction Mechanisms of Smectite Illitization Associated with Hydrothermal Alteration from Ponza Island, Italy

AbstractA hydrothermally altered rhyolitic hyaloclastite from Ponza island, Italy, has four alteration zones with unique clay assemblages: (1) a non-pervasive argillic zone characterized by smectite; (2) a propylitic zone with interstratified illite-smectite (I-S) containing 10–85% illite (I); (3) a silicic zone composed of I-S with ≥90% I and pure illite; and (4) a sericitic zone with I-S ranging from 66% I to pure illite. Atomic force microscopy reveals abrupt changes in particle morphology with illitization, including initial changes from anhedral plates to laths and then to euhedral plates and hexagonal plates. I-S particles progressively thicken with illitization and mean particle area (basal plane) remains constant from pure smectite to I-S with 80% I. However, particle area increases from 90 to 100% illite. Computer modeling of I-S structural forms indicates octahedral cation ordering progressively changes from cis- vacant smectite to interstratified cis- and tnuis-vacant I-S, and then to trans-vacant illite. In addition, polytypes progressively change from 1 Md to 1M, and then to 2M, illite. Electron-microprobe and X-ray fluoresence analyses show that I-S chemistry progressively changes during illitization, evolving toward a phengitic composition with ∼0.89 fixed interlayer K+ per O10(OH)2. Octahedral Mg2+ shows little change with illitization, varying from 0.3 to 0.5 cations per O,10(OH)2. The layer charge of smectite is ~0.38 equivalents per O10(OH)2.On the basis of abrupt changes in morphology and progressive changes in polytype and chemistry, smectite illitization on Ponza involved a dissolution and recrystallization mechanism with multiple stages of nucléation and crystal growth. In this multi-step model, temperature of alteration provided the major control for the layer composition, polytype, and morphology of I-S crystallites. Other factors that may play a secondary role include: K+ availability, water-rock ratio, and permeability. Alternatively, the mechanism of I-S and illite formation at Ponza and other hydrothermal environments may occur by direct precipitation of I-S crystallites from rhyolite glass and may not involve progressive reactions of smectite precursors.

Clay-Mineral Authigenesis in the Late Permian Coal Measures, Bowen Basin, Queensland, Australia

AbstractMineralogical studies were performed on authigenic clay minerals of mudrocks, sandstones, and bentonites from 38 boreholes in the Late Permian coal measures of the Bowen Basin. Clay-mineral separations of samples from the northern Bowen Basin consist mainly of (Reichweite, R) R = 1 and R ≥ 3 interstratified illite-smectite (I-S), chlorite, and kaolinite. In the southern Bowen Basin, samples from higher stratigraphie sections are characterized by randomly ordered (R = 0) I-S mixed layers, and kaolinite and chlorite in smaller amounts. Samples from the lower sections consist of (R ≥ 3) I-S, chlorite, chlorite-rich chlorite-smectite (C-S), and laumontite.Examination of the mineralogy and distribution of authigenic clay minerals from the Late Permian coal measures in the northern part of the Bowen Basin indicated that the presence of clay minerals is not systematically related to depth and clay occurrences do not occur regularly. These mineralogical variations of clay in volcaniclastic sediments are incompatible with thermal control. Variations in the rate of fluid flow and potassium supply owing to permeability exert major influences on clay-mineral paragenesis and the reaction of illitization. In more permeable zones (possibly faults or fracture zones), highly illitic clays with lath-shaped morphologies may have precipitated directly from potassium-rich fluids migrating from deeper parts of the basin. In addition, abundant chlorite precipitated contemporaneously with illitic clays, which may have resulted from sufficient magnesium and iron occurring in the fluids as a result of dissolution of intermediate or mafic-rock fragments. At the same time, clay paragenesis with less illitic I-S, kaolinite, and minor chlorite occurs outside the channelized zones of high fluid flow, where a diffusive-flow regime may have predominated with lower ratios of the activities of K+ and H+ (i.e., αK+/αH+) in the solutions.In the southern Bowen Basin, depth-related changes in the distribution of clay minerals are evident and may be indicative of thermal control on clay-mineral reactions. Zeolites are present locally in the Late Permian volcaniclastic rocks in the southern Bowen Basin, but not in the north. This is attributed to a low ratio of αCO2/αH2O (where α = activity) and/or more saline and alkaline solutions.

Transmission Electron Microscopy Study of Illitization in Pelites from the Iberian Range, Spain: Layer-by-Layer Replacement?

AbstractA sequence of interstratified illite-smectite (I-S) and illite in Paleozoic pelites and metapelites from the Iberian Range, Spain, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The fine-grained matrix of diagenetic pelites is composed of I-S with sequences of illite- and smectite-like layers in a given sample. The Reichweite (R) values as determined by XRD and averaged over heterogenous I-S layer sequences increase with increasing grade, apparently continuously, in sharp contrast with TEM observations of other published sequences. Changes in I-S sequences along layers are rarely observed. In the higher-grade diagenetic pelites, I-S coexists with illite. Each I-S phase has a composition similar to that of illite, implying unique Al-Si distributions in contrast to smectite and muscovite. Selected area electron diffraction (SAED) patterns of I-S and illite are diagnostic of 1Md polytypism. Anchizonal metapelites consist of larger packets of well-crystallized muscovite, with SAED patterns corresponding to a two-layer polytype.The continuous sequence of changes studied by TEM in I-S sequences and lateral transitions among these units is consistent with illitization by layer-by-layer replacement, although other processes are possible also. Replacement of individual layers probably occurs via fluids at reaction interfaces, in contrast to solid-state reactions, sensu strictu. The transition from the diagenetic to anchizonal rocks (transition in textures and formation of muscovite-2M1) occurred via dissolution/crystallization, however, presumably by tectonic stress. XRD and TEM data imply a consistent prograde trend in the sequence, the XRD data denning the average, long-range Reichweite ordering sequence, whereas the TEM data define the short-range layer sequences.

Preparation of Na-P1 and sodalite octahydrate zeolites from interstratified illite–smectite

The clay of Aidoudi (South Tunisia) which is an interstratified illite–smectite corresponding to the following analysis: SiO 2: 54.0%; Al 2O 3: 19.4%; Fe 2O 3: 6.7%; CaO: 0.2%; MgO: 1.5%; Na 2O: 2.3%; K 2O: 1.1% and a fire loss of 14.6% has been treated with 1 to 5 M NaOH solutions. Reaction has been performed on reflux during 2 to 24 h. The zeolitic products have been characterized by X-ray diffraction (XRD), infrared (IR) absorption, chemical analysis and SEM observations. For 1 and 1.5 M NaOH solutions zeolite Na-P1 was formed. It represents 47 and 58%, respectively, of the final solid corresponding to a reaction time of 24 h. For 2 to 5 M alkaline solutions sodalite octahydrate zeolite was obtained with yields up to 76% of the final solid. Cation exchange capacities towards ammonium cations have been determined. The final sodalite octahydrate zeolite has a CEC which increases from 167 to 367 mEq/100 g when temperature rises from 25 to 75°C whereas the Na-P1 zeolite presents a constant CEC equal to 270 mEq/100 g.

Some Comments on the Chemistry and Stability of Interstratified Illite-Smectite and the Role of Ostwald-Type Processes

AbstractMuch emphasis has been placed recently on the role of Ostwald-type processes (both ripening and the step rule) in the formation of interstratified illite-smectite clay minerals during diagenesis. Closer investigation of the relationships between illite particle thickness (as defined in terms of the fundamental particle theory) and particle chemistry show that simple Ostwald ripening is too simplistic a mechanism to describe observed changes in illite thickness and composition. In addition, available thermodynamic data on clay minerals suggest that the conventional notion of metastability associated with Ostwald's step rule is an inaccurate description of the relationship between illitic clay minerals and their macroscopic 2 : 1 phyllosilicate analogues.

Smectite to Illite Conversion in Bentonites and Shales of the East Slovak Basin

AbstractThe conversion of smectite to illite has been studied in buried bentonites and shales of the East Slovak Neogene Basin, using X-ray diffraction analysis and transmission electron microscopy. A good correlation was observed in both rock types between the content of expandable layers in interstratified illite-smectite (I-S) minerals and burial depth (temperature), with shales from a given depth being markedly more illitic than bentonties. This difference disappeared at a depth of ~3 km, which represents a temperature of ~150°C The diameter of fundamental illite particles increased with decreasing expandability. Potassium fixation together with neoformation appear to be the mechanisms of conversion of smectite to illite.

Least-squares profile of randomly interstratified clay mineral structures

A profile refinement method is described for the analysis of randomly interstratified clay mineral structures from their basal 00l reflections. The basis of the technique is similar to that of Rietveld refinement, allowing least-squares estimation of the variable parameters in the model, but a more elaborate calculation of the diffraction pattern is used including explicitly the effects of disorder and small particle size, via the analytical approximation of Wright [Clays Clay Miner. (1975), 23, 278–288] for random interstratification. The method allows the determination of the spacing and relative amount of each interlayer type, together with other information such as atomic z coordinates, site occupancies and the coherently diffracting domain size. Two examples are used as illustrations, a hydrated calcium montmorillonite and an interstratified illite–smectite soil clay. In both cases the results are shown to be an improvement on those previously obtained from the same diffraction patterns by more conventional methods. Although designed primarily for use in clay mineralogy, the method may also have applications in studies of other disordered systems such as graphite intercalation compounds and liquid crystals.

Clay mineral variation in Tertiary sediments from the eastern flank of the Niger Delta

AbstractDetailed clay mineralogical and chemical analyses of well cuttings of Tertiary sediments from two wells, Uruan-1 and Uda-1, on the eastern flank of the Niger delta, have been made in an attempt to investigate clay mineral burial diagenesis. The clay mineralogy indicates a transformation of smectite to an interstratified illite-smectite (I/S) phase. The relationship between ordered and random interlayering, however, is nonsystematic. The chemistry of the &lt;0·1 µm size fraction shows some tendency towards a net gain in K2O and Al2O3 and a net loss in SiO2 with depth, but the relationship does not correlate well with the thermal gradient. The distribution of kaolinite and chlorite in both wells appears to be unrelated in any regular way to smectite transformation and these two minerals are considered to be either the products of other diagenetic reactions affecting various stratigraphic levels, or the result of primary sediment deposition. In well Uda-1, kaolinite decreases in relative abundance with depth. This trend has been interpreted elsewhere as indicative of a transition from nonmarine to marine facies. The results of this study indicate that lack of ion mobility, rather than availability, is a significant factor in retarding the formation of ordered I/S with depth, and that lithology, overpressuring, carbonate cement, and original smectite layer charge may be controlling factors in the smectite → illite transformation.

Interstratified XRD characteristics of physical mixtures of elementary clay particles

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