Platy Particles Research Articles

Preparation and Porous Properties of Materials Prepared by Selective Leaching of Phlogopite

AbstractPorous silica products obtained by selective leaching of phlogopite using an acid solution were investigated by XRD, MAS NMR, SEM, TEM, DTA/TG, and N2 and Ar gas adsorptions. The phlogopite powder was leached by a nitric acid solution at various concentrations (0.01–10 M) at 5–150°C for 10 min–480 h. Selective leaching of the phlogopite powder became extensive when the concentration of nitric acid was >1 M. Only SiO2 remained after the treatment, the other components (MgO, Al2O3, K2O and Fe2O3) being selectively leached from the product. At higher leaching temperatures, the leaching rate became faster and the resulting maximum specific surface area of the porous silica product became larger at each leaching temperature. The porous silica products were found by SEM and TEM, to maintain their original platy particle shape even after the selective leaching. The 29Si MAS NMR spectra of the products, however, revealed that the linkage structure of SiO4 tetrahedra converted to a framework type from a layered type in the original phlogopite. The porous silica product with the maximum specific surface area (532 m2/g) was obtained by leaching in a nitric acid solution with concentration of 5 M at 90°C for 15 min. The pore-size distribution of the porous silica product was bimodal with micropores of ∼0.7 nm and mesopores of ∼4 nm. The pore size of the products changed from 0.7 nm to 4 nm and further to 6 nm with increased leaching time. The present results are discussed in relation to those reported for phlogopite by other workers.

Atomic Force Microscopy Study of Hydrothermal Illite in Izumiyama Pottery Stone from Arita, Saga Prefecture, Japan

AbstractThe surface microtopographic observations and analyses of Izumiyama hydrothermal illite particles were made by utilizing tapping-mode atomic force microscopy (TMAFM). The Izumiyama illite particles showed platy to lath shapes. Platy particles exhibited various spiral growth patterns, i.e. circular, malformed circular, or polygonal single unit-cell layer spirals, polygonal parallel step spiral, or interlaced spiral patterns. The polygonal parallel step spiral and interlaced spiral patterns are formed by two single unit-cell layers rotated by 180° and 120° arising from a single screw dislocation point, respectively. The spiral patterns indicate that the illite particles have 1M, 2O and 2M1 polytypes. Lath-shaped particles show only interlacing patterns supporting the formation of 2M1 structures.Particles showing circular or malformed circular spirals were found to be thinner and to have narrower step separations than particles showing polygonal spirals. Polygonal platy and lath-shaped particles showing interlaced patterns tended to be thicker and to have wider step separations than the other polygonal platy particles.These results suggest that the Izumiyama illites crystallize as the result of a mechanism involving solution-mediated polytypes and spiral-type transformations of illite. The mechanism involves the Ostwald ripening process, i.e. a transformation of the polytype and spiral shape. The sequence of crystallization of the Izumiyama illite is: 1M circular spirals → 1M, 2O polygonal spirals → 2M1 polygonal spirals occurring during crystal growth and sequentially overgrowing on the initial particle surfaces. The super-saturation of the hydrothermal solution probably decreases gradually during the transformation, and this decrease may cause not only the transformation from a circular to a polygonal crystal morphology but also the development of a lath habit due to the inhibition of the growth rate in the [010] direction of the particle.

The Relationships between Kaolinite Crystal Properties and the Origin of Materials for a Brazilian Kaolin Deposit

AbstractThe clay particles in a kaolin deposit from Brazil were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), analytical transmission electron microscopy (ATEM), and electron paramagnetic resonance (EPR) to examine the relationships between morphological and chemical properties of the crystals and to relate these properties to formation conditions. The XRD patterns show the dominant presence of kaolinite with minor amounts of gibbsite, illite, quartz, goethite, hematite, and anatase. ATEM observations show two discontinuities in the deposit as indicated by changes in morphology and size of the kaolinite crystals. At the base of the deposit, hexagonal platy and lath-shaped particles (mean area of 001 face = 0.26 μm2) maintain the original fabric of the parent rock which characterizes an in situ evolution. In the middle of the deposit a bimodal population of large (mean area of 001 face > 0.05 μm2) and small (mean area of 001 face < 0.05 μm2) sub-hexagonal platy kaolinite crystals occurs. This zone defines the boundary between the saprolitic kaolinite and the pedogenic kaolinite. Near the top of the profile, laths and irregular plates of kaolinite, together with sub-hexagonal particles, define two different depositional sources in the history of formation of the deposit. Crystal thickness as derived from the width of basal reflections and the Hinckley index are compatible with the morphological results, but show only one discontinuity. At the base of the deposit, kaolinite has a low- defect density whereas in the middle and at the top of the profile, kaolinite has a high-defect density. Likewise, EPR spectroscopy shows typical spectra of low-defect kaolinite for the bottom of the deposit and typical spectra of high-defect kaolinite for the other portions of the deposit. Despite the morphological changes observed through the profile, the elemental composition of individual kaolinite crystals did not show systematic variations. These results are consistent with the deposit consisting of a transported pedogenic kaolinite over saprolite consisting of in situ kaolinized phyllite.

Diagenesis of silica minerals from clay minerals in volcanic soils of Mexico

AbstractIndurated volcanic soils (tepetates) of the Mexican Altiplano display thick columnar horizons, hard laminar horizons, and grey mottles at depth. X-ray diffraction (XRD) studies show a relative enrichment in cristobalite vs. halloysite in the indurated plates of the laminar horizons and in the clay fraction of the mottles. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies of these two soil components have shown that they are composed of small tubes of halloysite in which numerous globular grains ∼1 μm in diameter are embedded. Based on the relative abundance of cristobalite in pedological features and on the spatial relations between successive mineral phases, we interpret the cristobalite as a transformation of halloysite with a transitional amorphous phase. In the globular grains, large platy 1:1 clay minerals undergo a progressive transformation into platy particles of opal-A and opal-C. These are in turn transformed into cristobalite without further major change in their shape and appearance, except for a higher electron density than opal and clay.

Fabrication of Ag-sheathed Bi–Sr–Ca–Cu–O thick films by a novel a.c.-electric field assisted electrophoretic deposition method

Ag-sheathed Bi 2Sr 2CaCu 2O δ (BSCCO) tapes with improved microstructural and superconducting properties have been fabricated using a novel electrophoretic deposition technique which involves an application of an alternating current (a.c.) field parallel to the substrate surface in addition to a direct current (d.c.) field during the film deposition. Due to the presence of the additional a.c. field stronger than d.c. field, the angular vibration of BSCCO platy particles along the field direction decreases within the framework of the model of suspended particles. This results in the higher probability of orientation, and hence, deposition of particles with major faces parallel to the a.c. field causing an improvement in the c-axis texturing in green BSCCO films which is key to the fabrication of final BSCCO tapes with predominantly c-axis textured grains. The critical current density ( J c) measured using maximum magnetization data indicates that J c's of a.c. field assisted electrophoretically deposited BSCCO tapes (10 6–10 5 A/cm 2 at 5 K) are 1–2 orders of magnitude higher than that of electrophoretically deposited BSCCO tapes (8×10 4–7×10 2 A/cm 2 at 5 K) without a.c. field.

Gas adsorption properties of mesoporous γ-alumina prepared by a selective leaching method

Gas adsorption properties of mesoporous γ-Al 2 O 3 prepared by the selective leaching method were investigated using various adsorbate gases. The mesoporous γ-Al 2 O 3 was prepared by calcining kaolinite to form a microtexture of fine γ-Al 2 O 3 grains dispersed in a matrix of amorphous SiO 2 followed by selective leaching of amorphous SiO 2 from the microtexture. The mesopores were formed inside the pseudomorphic hexagonal platy particles of kaolinite. The specific surface area, total pore volume and pore size measured at 77 K using N 2 gas were ca. 240 m 2 g –1 , 0.7 ml g –1 and 6 nm, respectively. The gas adsorption isotherms of polar molecules such as water, methanol and butan-1-ol showed type IV isotherms (IUPAC classification) while those of non-polar molecules such as cyclohexane showed type V isotherms. The γ-Al 2 O 3 was therefore recognized as having hydrophilic surface characteristics. The onset of adsorption of these gases in the low relative pressure (P/P 0 ) region was methanol>water>butan-1-ol>cyclohexane, this order corresponding to the affinity between the adsorbate gas and surface of the γ-Al 2 O 3 and also reflecting the steric effect of adsorbate gas. The fractal dimension obtained from the BET monolayer adsorption capacity plot was 2.1, indicating a smooth surface. The gas adsorption properties of the γ-Al 2 O 3 are discussed and compared with commercial γ-Al 2 O 3 and Al 2 O 3 -SiO 2 gel.

Surface microtopography of rectorite (allevardite) from Allevard, France

AbstractBy means of transmission electron microscopy (TEM) and the gold decoration technique, the surface microtopography of rectorite (allevardite) crystals collected from Allevard, France was investigated. On the crystal surfaces, gold decoration successfully revealed growth steps of ∼20 Å in height. Only closed polygonal steps 20 Å high occur on the 001 surface of a thick platy crystal, although spiral growth patterns were not observed. Thick platy particles were easily split into thinner plates 20 Å thick in distilled water by means of ultrasonic vibration. No step patterns were observed on the surfaces of these thin plates which correspond to the cleavage plane. The growth of this rectorite, therefore, seems to be controlled by a layer nucleation mechanism.

Effects of Grinding Aids on the Surface Properties of Flaky Graphite

Dry grinding of raw flaky graphite was carried out using a planetary mill in the presence of additives such as tri-sec-butylaluminate, 1H, 1H, 5H-octafluoropentanol and 1-pentanol. Each of the additives proved effective in accelerating the size reduction of the graphite, along with in making thin platy particles. The agglomeration of powders and the ball coating were not observed during the grinding, indicating that the additives spread over on all surfaces including the newly born surface of the particles resulting in a decrease in surface energy. Fluoropentanol having a high acidity showed a relatively higher effectiveness of grinding aids than 1-pentanol. The function of the aids for thinning particles has been explained; i.e., the chemisorption of the additive molecules on the broken bond plane of the graphite probably facilitates the fracture of particles along the cleavage planes.

Formation of Mica During Experimental Alteration of K-Feldspar

AbstractExperimental alterations of K-feldspar in distilled-deionized water at 150°, 175°, 200°, and 225°C were performed. The alteration products and dissolution mechanism of K-feldspar were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). SEM, TEM, and EDX clearly showed formation of fibrous boehmite less than 1.0 μm in length at the early alteration stages. The boehmite fibers decreased in abundance and rounded platy 1 M mica was produced as alteration proceeded. The mica exhibited initially angular shaped small flakes of 0.69 μm in average size, which developed to rounded platy particles of 1.97 μm. The main chemical reactions occurring in this experimental system can be expressed by: $$\begin{array}{l} \mathop {KAlS{i_3}{O_3}}\limits_{\left[ {K - feldspar} \right]} + 6{H_2}O + {H^ + } \to \mathop {AlO\left( {OH} \right)}\limits_{\left[ {boehmite} \right]} + 3{H_4}Si{O_4} + {K^ + }, \\ \mathop {3KAlS{i_3}{O_8}}\limits_{\left[ {K - feldspar} \right]} + 12{H_2}O \to \mathop {KA{l_3}S{i_3}{O_{10}}{{\left( {OH} \right)}_2}}\limits_{\left[ {mica} \right]} + 2{K^ + } + 6{H_4}Si{O_4} + 22{H^ + }. \\ \end{array}$$ XPS showed no significant changes in intensities of photoelectron lines excited from K, Si, and Al in the K-feldspar surface before and after alteration, however the K/Si molar ratios in the solutions were considerably smaller than that of the original K-feldspar. The results of XPS strongly indicate that no dealkalized layer was produced on the surface, and that dissolution of K-feldspar in aqueous solution proceeded congruently by a surface-reaction mechanism. The discrepancy of mass balance in the solutions may be mainly caused by adsorption of K on the surface of boehmite.

電気的検知帯法およびレーザー回折法による粒度分布測定に及ぼす粒子形状の影響

There are many types of particle size analyzers, but the size of the measured particle varies depending on the analyzer used. In this study, the effects of particle shape on the results of various particle size data were examined for three types of particle size analyzers, i. e. an optical microscope, a Coulter counter and the laser diffraction method. In a Coulter counter, mean particle size from spherical, blocky and cubical particles agreed when using the microscopic method, but prismoidal and platy particles measured smaller with that method. When the laser diffraction method was used the mean particle size from spherical, blocky and platy particles agreed with the results of the microscopic method, but cubical particles measured larger and prismoidal particles measured smaller.Because of this, a technique was proposed for estimating the mean particle size using an optical microscope from mean particle size obtained a Coulter conter or the laser diffraction method. This technique can be used to compare the measured mean particle size using a Coulter counter in combination with a laser diffraction method without the influence of particle shape.

Mineralogy of Rhizospheric and Non-Rhizospheric Soils in Corn Fields

AbstractTechnical limitations have restricted investigations of rhizosphere mineralogy. Various analytical techniques were applied to assess root-mineral associations and dynamics in natural soils under corn production. Soil samples were collected between four and five weeks after planting and included rhizospheric and non-rhizospheric soils, and undisturbed block samples containing corn root systems. Analytical techniques were applied and included; X-ray diffraction, optical microscope, SEM, EDXRA with SEM, transmission electron microscope (TEM), electron energy loss spectra with TEM, high-resolution transmission electron microscope (HRTEM) and microanalysis with HRTEM. The mineralogy of the rhizosphere differed from that of the bulk soil. Within the rhizosphere, minute platy particles which were mostly vermiculitic minerals, were particularly concentrated near or on root surfaces. These platy mineral particles were not attached to the entire area, but only to certain areas of root surfaces. Therefore, we report quantitative evidence for mineralogical changes in the rhizosphere in soil environments.

Double-Layer Repulsive Force between Two Inclined Platy Particles According to the Gouy-Chapman Theory

Using the Gouy-Chapman theory of electrical double layer, the nature of repulsive force between two nonparallel platy particles of finite length immersed in 1:1 electrolytes is examined, The potential distribution around the plates are computed by solving the Poisson-Boltzmann equation with the aid of a finite difference numerical technique. The magnitude and location of the net repulsive force between the plates are then computed for a range of values of geometrical parameters and surface potential. The results indicate that as the angle between particles increases, the magnitude of repulsive force decreases very quickly, and the location shifts toward the closest ends. It is also shown that the force computed by a simplified method based on Derjaguin's approximation compares reasonably well with that computed by the finite difference numerical method. The simplified method should provide a reasonable and fast means of computing repulsive force in semiquantitative analyses of colloidal systems consisting of platy particles.

Sedimentary structures on the Bengal shelf: a multi-scale approach to sedimentary fabric interpretation

Sedimentary structures on the Bengal shelf are examined using X-radiographic, thin-section, and scanning-electron-microscopic (SEM) techniques, which reveal contrasting depositional processes for the inner and middle shelf as well as for either side of a major submarine canyon indenting the western shelf margin. The inner shelf is characterized by tidally produced interlaminated silts and muds that reveal a neap-spring cyclicity. The cyclicity is more pronounced for the winter season, when high-discharge/monsoon conditions do not obscure the tidal signature. On the middle shelf, alternating beds of silts and muds probably represent high-discharge and low-discharge conditions, respectively. Silty beds on the western margin of the submarine canyon are thinner than those found on the eastern margin. The western margin receives predominantly fine-grained Ganges sediments, in contrast to the eastern area which receives both Ganges and coarser Brahmaputra sediments; these observations indicate that the submarine canyon presently intercepts westward along-shelf sediment transport. Muddy beds and laminae that appear internally homogeneous in the X-radiographs and exhibit faint bedding in thin sections often are composed of resistant (protruding) and less-resistant (recessed) microlaminae as observed with the SEM. On the inner shelf, resistant microlaminae are composed of fine-grained polymineralic, equant particles. The less-resistant microlaminae are composed of large, platy illite grains rimmed by smaller platy or lath-like illite particles. Resistant and less-resistant microlaminae within middle-shelf muddy sediments have the same textural characteristics observed on the inner shelf; however, both types essentially are monomineralic. On the middle shelf the smallest particles within the less-resistant microlaminae exhibit an open flocculated structure that may result from higher salinity, and/or decreased bottom shear stress associated with tidal currents. Biological structures predominantly occur on the western inner and middle shelf, particularly in intervals of high smectite concentrations. This relationship may exist because of a preferential organic affinity for expandable minerals, providing a favorable substrate for benthic organisms.

The significance of oil shale fabric in primary hydrocarbon migration

Scanning electron microscopy (SEM) and thin-section analysis of the fabrics (particle orientation) of some well known ‘oil shales’ reveal they all share two common characteristics: (1) even though preferred platy particles dominate, there is present an open network of numerous interconnecting pores; and (2) fine lamination of alternating silt and organic clay-rich zones is common. Shales selected for analysis include the Woodford Shale, Sunbury Shale, torbanite, Rundle Shale and Ohio Shale (Huron Member), West Falls Formation (Rhinestreet Member), New Albany Shale (Clegg Creek Member) and the Exshaw Formation. A model is proposed, based upon fabric information, for the migration of hydrocarbons from source rocks. Hydrocarbons generated in organic-rich zones migrate through the micropores until reaching adjacent silt laminae, which act as ‘pipelines’ to facilitate further migration out of the source rock.

Preparation of Magnesium Nitride Powder by Low‐Pressure Chemical Vapor Deposition

Submcrometer‐scale magnesium nitride (Mg3N2) powder was prepared by low‐pressure chemical vapor deposition, i.e., the reaction of Mg vapor with mixed NH3–N2 gases at 800°C under a pressure of ∼1 kPa. The mixing ratios of NH3–N2 gases were 0% NH3–100% N2 (pure N2), 20% NH3–80% N2, 40% NH3–60% N2, 60% NH3–40% N2, 80% NH3–20% N2, and 100% NH3–0% N2 (pure NH3). The reactions between Mg vapor and NH3–N2 gases produced platy Mg3N2 particles <0.2 μm and acicular particles with long‐axis length of ∼0.2 μm, whereas the reaction of Mg vapor with pure NH3 gas produced spherical Mg3N2 particles with diameters of ∼0.1 μm.

The manganese oxide mineral, lithiophorite, in an oxisol From Hawaii

The mineralogical composition of the surface soil horizon (0-15 cm) of Wahiawa soil (Tropeptic Eutrustox) was investigated by X-ray diffraction (XRD), high gradient magnetic separation (HGMS), transmission electron microscopy (TEM), and infrared methods. The concentration of lithiophorite decreased with particle size and none was present in the clay fraction as indicated by XRD. Lithiophorite was further concentrated from the crushed sand-sized fraction by HGMS. Hexagonal, electron-dense, often twinned lithiophorite particles were identified by electron diffraction. Differential infrared (DIR) spectra obtained by dissolving Mn oxides in acidified hydroxylamine hydrochloride (HAHC) indicated lithiophorite as the HAHC-soluble Mn-phase. Lithiophorite compositiion, as revealed by chemical analysis of the HAHC extracts, consisted of appreciable amounts of Mn, Al, Zn, Co and Mg, and less than stoichiometric amounts of Li. Sodium hydroxide treatment apparently altered the lithiophorite, as revealed by the DIR spectrum of the hydroxylamine-soluble fraction of the NaOH-treated sample compared with the untreated sample. The high crystallinity of the lithiophorite was suggested by its resistance to chemical dissolution and narrow X-ray diffraction lines. No evidence for the presence of todorokite or birnessite was found, contrary to earlier reports. Examination of sand-sized nodules by scanning electron microscopy indicated large (2-5 �m) platy lithiophorite crystals at the surface of these nodules. Electron microprobe analysis of these platy particles indicated iron enrichment near the surface. The freshly fractured nodule surface revealed numerous unaltered platy crystals of lithiophorite filling the veins of the nodule.

Internal structure and occurrence of accretionary lapilli ? a case study at Laacher See Volcano

Accretionary lapilli are common in fine-grained pyroclastic flow and surge deposits and related co-ignimbrite/co-surge ash layers of Laacher See volcano. Two morphologically different types are distin-guished: (1) Rim-type lapilli are composed of a coarse-grained core surrounded by a fine-grained rim. Rims are internally graded or made up of several layers of alternating fine and very-fine grained ash. (2) Core-type lapilli lack fine-grained rims. Field relationships, internal, and grain-size characteristics are specific to accretionary lapilli from different types of tephra deposits. Accretionary lapilli may therefore be a helpful tool to infer the origin of tephra of different origin. In co-ignimbrite ashfall, accretionary lapilli are generally concentrated at the base, whereas pyroclastic flow and surge deposits contain lapilli in the upper parts of individual, thin-bedded layers. Rim-type lapilli are found in pyroclastic flow and surge deposits up to 4 km from the source. Core-type lapilli occur at greater distances or are associated with vesiculated tuffs where they are within 1 km from the vent. Accretionary lapilli from co-ignimbrite/co-surge ash show open framework textures and edge-to-face contacts of individual ash particles. Vesicularity is generally low but the overall porosity of 40% to 50% results in an average density of 1200 kg/m3. Accretionary lapilli in pyroclastic flow and surge deposits are more densely packed and platy particles are often in face-to-face contacts. Vesicularity of those from pyroclastic flow deposits is significantly higher; the overall porosity is about 30% to 40% and the average density 1600 kg/m3. Grain-size analyses show that the accretionary lapilli in co-ignimbrite/co-surge ashfall deposits are the most fine-grained with a median (Md) of 20 to 30 μm and a maximum grain size of 250 to 350 μm. Accretionary lapilli from pyroclastic flow deposits have intermediate Md-values of 30 to 50 μm and a maximum grain size of 350 to 500 μm. Those of surge deposits are the coarsest grained with Md-values of 30 to >63 μm and a maximum grain size up to 2 mm.

Sintering of Platelike Iron(III) Oxide Powders

Packing and sintering of platelike hematite powders were studied with a special emphasis on pore behavior, and the results were compared with those for acicular powders. Platy particles gave a relatively high green density of 65% of the theoretical value, but did not achieve high fired densities. This is in strong contrast to acicular powders, in which high fired densities were reached from a relatively low green density under the same firing conditions. Features observed with platy particles have been interpreted as being due to the wedgelike pores which tend to close at the early stages of densification.

Stress, shear deformation and micromorphological clay orientation: A synthesis of various concepts

Microscopic oriented clay bodies known as plasma separations to soil micromorphologists show various degrees of symmetry and regularity in their patterns. They could be regarded as sensitive and reliable indicators of stress-strain regime of a soil. Empirical and experimental evidence signifies the importance of stress, specifically that generated by in situ swelling, in the genesis of plasmic fabrics. Hitherto, most work in this field is confined to geometric characterization, with limited attempts to dynamic interpretations of their origin. This paper enlists appropriate concepts in soil mechanics, structural geology and agricultural engineering to interpret the possible stress-strain components that rearrange fabric units into plasma separations. Some pertinent concepts, including physico-chemical behaviour of the clay-water system, shrink-swell phenomenon, stress-strain, deformation and failure of soil, are employed to explain the origin of plasmic fabrics by mechanical principles. A conceptual model is suggested to synthesize the conditions, changes and consequences related to the formation of plasmic fabrics. Strongly developed plasma separations in natural soils are attributed to the establishment of an anisotropic state of stress generated by in situ swelling, in conjunction with the passive pressure of lateral confinement and vertical overburden. The difference between the maximum and minimum principal stresses produces a deviatoric stress that can, at certain stages of a shrink-swell cycle, exceed the shear strength of the soil. The extra stress is relieved plastically by shear deformation which is manifested as the alignment of platy particles in domain configuration by rotation and translation along the shear planes. Soil mainly fails in compressive (plastic) mode along a large number of small shear planes which form the plasma separations. The formation of different types of sepic plasmic fabrics is discussed in relation to the stress-strain regimes of soils.

S.E.M. study of clastic fabrics preserved in calcareous concretions from the late-Devensian Errol Beds, Tayside

Synopsis S.E.M. studies of the clastic components of calcareous concretions from the late-Devensian, glaciomarine Errol Beds near the type site, east-central Scotland, reveal fabrics indicative of deposition from originally flocculated suspensions. Previously undescribed spherical cavities 30–350 μm in diameter, characteristically fringed by aligned platy particles, are thought to have been former gas bubbles around which the grains adhered by surface tension. It is suggested that the gas was ammonia, believed to have been derived from the decay of proteinaceous organic matter which promoted localised CaCO 3 precipitation through a rise in pH. The delicate, porous fabrics preserved via cementation indicate that the concretions are of early diagenetic origin and formed rapidly, close to the sediment–water interface. In contrast, the fabrics shown by the host clays are consistent with consolidation of originally flocculated materials.