Spheroidal Halloysite Research Articles

Pozzolanic activity of calcined halloysite-rich kaolinitic clays

The aim of this study is to determine the pozzolanic activity of clays with high content of halloysite/kaolinite, and to evaluate the influence of halloysite/kaolinite ratio and halloysite morphology in the development of pozzolanic activity of the calcined clays. For this purpose, three different natural clays from Río Negro Province, Argentine, were selected and completely characterized. After calcined at 700°C and ground to 80% of particle size <45μm, pozzolanic activity was determined using the electrical conductivity test, the Frattini test and the compressive strength index. Results show that all calcined clays are classified as high reactive pozzolana. The presence of kaolinite and spheroidal halloysite exerts great influence at early ages; while tubular halloysite has greater influence in the pozzolanic activity and the compressive strength of mortars at later ages.

A new attraction-detachment model for explaining flow sliding in clay-rich tephras

Abstract Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatalities and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in deposits with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landsliding, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggregates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite.

The origin of spheroidal halloysites: a review of the literature

AbstractTubular halloysite has many applications as a nanomaterial. Spheroidal halloysite (SPH) is the other most common form of halloysite. Its mode of formation has had different explanations, including association with allophane, or more generally, following weathering of volcanic glass. Some SPHs have formed from minerals in crystalline rocks, sometimes as an early stage of evolution into plates and/or tubes of halloysite and ultimately to kaolinite. Spheroidal halloysites can show a range of Fe contents and can occur with other forms of halloysite; they have often formed in confined environments whereas tubular halloysites apparently form in more open spaces. They have also formed on microbes or where there is a significant amount of organic matter. Generally, SPHs have often formed by rapid dissolution of volcanic glass and primary minerals. The SPHs can persist over time. They have fewactive edges, so interparticle interaction is poor, causing low viscosities in clay-water suspensions, poor soil stability and low adsorption capacities.

Spheroidal halloysites from Patagonia, Argentina: Some aspects of their formation and applications

Halloysite deposits in Argentina have been identified in the province of Río Negro (Patagonia). The mineralized area occurs as altered zones in Eocene volcanic–pyroclastic rocks, dacitic to rhyolitic in composition. A comprehensive study of these deposits was carried out by means of mineralogical, geochemical and isotopic analyses.Intense weathering has transformed the whole rock to a white mass composed of 75% –90% halloysite+kaolinite, with cristobalite, tridymite, and quartz, as the main non-clay minerals. Ferruginous beidellite and titanium minerals are also present in minor amounts.The halloysite–kaolinite ratio ranges from 75 to 25 to 100–0. Due to the alteration of very dense rocks, halloysite morphology is predominantly spheroidal. Tubular halloysite is the main constituent in more porous rocks, but the latter are scarce in the area.Because of the predominance of the spheroidal type, the use of halloysite as HNT (halloysite nanotube) is not feasible. Nonetheless, this mineral can be modified by different organic molecules, and used to remove pollutants such as emulsified hydrocarbons and heavy metals. A special product made with this halloysite is used as sunscreen when sprayed on fruits in areas of intense solar radiation. The whiteness of this mineral is not very high due to the amount of titanium oxide present in its composition (about 1%). Nevertheless, titanium oxide is present as individual particles, so it could be removed by a mechanical process.New applications for spheroidal halloysite are currently being investigated. Moreover, depending on the price and demand, the tubular halloysite of low grade deposits could be exploited.

Mineralogy of volcanically derived alluvial soils at Moshi, Tanzania

Despite intensive commercial agriculture in the rift zone of Tanzania, mineralogical studies on the soils influenced by volcanic parent materials are scarce. A mineralogical investigation of the soils and two buried ash layers from an irrigated sugar estate was undertaken using X-ray diffraction, transmission electron microscopy and measurements of extractable iron, aluminium and silicon and the specific surface area (SSA) of the clay fraction. The dominant mineral in the sand and silt fractions was sanidine. The clay fractions contained mainly high-defect kaolin, illite and K-feldspar, with small amounts of calcite, talc and gibbsite in some samples. Electron microscopy revealed the presence of tubular and spheroidal halloysite and &lt;0.5µm kaolinite crystals, as well as nanocrystalline material, probably allophane, and volcanic glass. The amounts of ferrihydrite (0.34–1.84%) and allophane (0.52–6.84%) were low in the soils but higher in the buried ash layers. The surface areas of the clay fractions were high (up to 145m2g–1) and it was calculated that 5% allophane constituted 22% of the total SSA. Although all soils were dominated by halloysite and small kaolinite particles, it is likely that the small amounts of allophane with high SSA has a strong effect on their physical and chemical properties.

Native Morphology of Hydrated Spheroidal Halloysite Observed by Environmental Transmission Electron Microscopy

AbstractNatural mineral materials such as tabular and spheroidal halloysites have recently been suggested as candidates for intercalating metal ions or organic molecules. Their potential use as nanoadsorbents is related to their porous structure and water content. Although the two morphologies can coexist in natural deposits, spheroidal halloysites remain poorly characterized whereas much literature exists on tubular halloysites. The present study investigates the native morphology, internal porous structure, and behavior upon dehydration of spheroidal halloysite from Opotiki (New Zealand). This mineral was characterized in its natural hydrated state using a transmission electron microscope equipped with an environmental cell (EC-TEM). The sample was placed in a sealed block in which water vapor-saturated air circulated at a pressure of 30 Torr. The observed particles consisted of almost complete spheroids displaying polyhedral external surfaces. 1:1 layers stack concentrically as a pore-free, onion-like structure. The dynamic processes of dehydration created by slow depressurization of the cell resulted in a decrease in the layer-to-layer distance (d001) from ~10 Å to ~7 Å due to the loss of interlayer water molecules. Irreversible formation of spurious ‘internal pores’ was recorded during this process. These pores were not indigenous to the hydrated 10 Å halloysite and resulted from the collapse of the native layers. They cannot account for the physical chemical properties of spheroidal halloysite. Spheroidal halloysites would have a lower propensity for intercalating ions or molecules than tubular halloysites. Isolated facets were also observed in high-resolution-TEM and displayed a pseudo-hexagonal morphology. The three-dimensional microstructure of the spheroid appeared bent along the three pseudo equivalent yi directions of the kaolinite-like single layers. An analogy with polyhedral serpentine has allowed the proposal of a formation process of hydrated spheroidal halloysite triggered by enrichment in divalent ions in the growth system.

Halloysite in Argentinian deposits: origin and textural constraints

AbstractIn Argentina, the only halloysite deposits found so far are located in the southwest of the province of Rio Negro. The areas are named Mamil Choique and Buitrera, separated by 50 km in a W–E direction. The deposits are located in pyroclastic rocks, rhyolitic tuffs and ignimbrites.The aim of this paper is to determine the origin of the alteration, any relationship between the processes in Mamil Choique and Buitrera, and the factors which controlled the halloysite formation. The work was based on field work, mineralogical and geochemical studies, form and distribution of the alteration. Fresh as well as altered rocks were collected. The first were studied by petrographic and chemical methods. In altered samples, the clay mineralogy was determined by XRD and textures by SEM and TEM. Chemical analyses on fresh and altered samples were used to characterize the alteration process and the rock composition.It was concluded that halloysite has been formed by weathering in a time range from Middle Eocene to Middle Oligocene and extended along 50 km in a W-E direction, independent of the source rock. Particle morphology depends on the original texture of the rock. Spheroidal halloysite is related to rocks with low porosity and tubular particles are related to rocks with open spaces.

Progressive Stages in the Formation of Kaolin Minerals of Different Morphologies in the Weathering of Plagioclase

AbstractHalloysite and kaolinite occur in gneissic weathering profiles developed under a temperate climate in the Leucogia area of NE Greece. X-ray diffraction analyses of samples from three profiles of partially weathered gneisses have revealed that kaolinite becomes more abundant than halloysite with increasing intensity of the decomposition processes. To resolve the genetic relationship between halloysite and kaolinite, microtextures were examined by scanning electron microscopy using polished thin-sections and freshly exposed fracture surfaces, and their chemical compositions were determined using an analytical scanning electron microscope fitted with energy dispersive and wavelength dispersive spectrometers. Different morphological forms of halloysite and kaolinite were detected within the same rock mass. In the earliest stage of weathering, spheroidal aggregates consisting of microcrystalline halloysite are formed on the plagioclase surface. With progressive weathering, spheroidal halloysite converts to tubular halloysite. As weathering advances, tubular halloysite converts to platy halloysite, which in turn converts to kaolinite. Halloysite and kaolinite may coexist in the upper parts of the profiles. Electron microprobe analyses of spheroidal, tubular and platy halloysite and kaolinite show that the chemical composition of the various forms indicate a progressive Fe enrichment and Al depletion with advancing kaolinization, from VIFe0.08VIAl3.70 a.p.f.u. in spheroidal halloysite through VIFe0.29VIAl3.50 in platy halloysite to VIFe0.53VIAl3.32 in newly formed kaolinite. Final-stage, book-type kaolinite approaches its ideal chemical composition (VIFe0.04VIAl3.95). The mineralogy and composition of the kaolin minerals and the development of the various morphological forms of halloysite and kaolinite in different parts of the profiles are attributed to the chemistry of the ambient solutions. However, other physical and microenvironmental conditions (e.g. time and space available) also seem to have strong influence on the precipitation processes producing the morphological variations.

Phyllosilicate‐poor palagonitic dust from Mauna Kea Volcano (Hawaii): A mineralogical analogue for magnetic Martian dust?

The mineralogical and elemental composition of dust size fractions (&lt;2 and &lt;5 μm) of eight samples of phyllosilicate‐poor palagonitic tephra from the upper slopes of Mauna Kea Volcano (Hawaii) were studied by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), visible and near‐IR reflectance spectroscopy, Mössbauer spectroscopy, magnetic properties methods, and transmission electron microscopy (TEM). The palagonitic dust samples are spectral analogues of Martian bright regions at visible and near‐IR wavelengths. The crystalline phases in the palagonitic dust are, in variable proportions, plagioclase feldspar, Ti‐containing magnetite, minor pyroxene, and trace hematite. No basal reflections resulting from crystalline phyllosilicates were detected in XRD data. Weak, broad XRD peaks corresponding to X‐ray amorphous phases (allophane, nanophase ferric oxide (possibly ferrihydrite), and, for two samples, hisingerite) were detected as oxidative alteration products of the glass; residual unaltered glass was also present. Mössbauer spectroscopy showed that the iron‐bearing phases are nanophase ferric oxide, magnetite/titanomagnetite, hematite, and minor glass and ferrous silicates. Direct observation by TEM showed that the crystalline and X‐ray amorphous phases observed by XRD and Mössbauer are normally present together in composite particles and not normally present as discrete single‐phase particles. Ti‐bearing magnetite occurs predominantly as 5–150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass. Rare spheroidal halloysite was observed in the two samples that also had XRD evidence for hisingerite. The saturation magnetization Js and low‐field magnetic susceptibility for bulk dust range from 0.19 to 0.68 Am2/kg and 3.4×10−6 to 15.5×10−6 m3/kg at 293 K, respectively. Simulation of the Mars Pathfinder Magnet Array (MA) experiment was performed on Mauna Kea Volcano in areas with phyllosilicate‐poor palagonitic dust and with copies of the Pathfinder MA. On the basis of the magnetic properties of dust collected by all five MA magnets and the observation that the Pathfinder MAs collected dust on the four strongest magnets, the value for the saturation magnetization of Martian dust collected in the MA experiments is revised downward from 4±2 Am2/kg to 2.5±1.5 Am2/kg. The revised value corresponds to 2.7±1.6 wt % magnetite if the magnetic mineral is magnetite (using Js = 92 Am2/kg for pure magnetite, Fe3O4) or to 5.0±3.0 to 3.4±2.0 wt % maghemite if the magnetic mineral is pure maghemite (using Js = 50 to 74 Am2/kg for pure maghemite, γ‐Fe2O3). Comparison of the magnetic properties of bulk Mauna Kea palagonitic dust to those for dust collected by MA magnets shows that the MA magnets extracted (culled) a subset (25–34 wt %) of composite magnetic particles from bulk dust. The extent of culling of Martian dust is not well constrained. Because the Mauna Kea palagonitic dust satisfies the essential constraints of the Pathfinder magnetic properties experiment (composite and magnetic particles capable of being collected by five MA magnets), a working hypothesis for the strongly magnetic mineral present in Martian dust and soil is magnetite (possibly Ti‐bearing) formed by rapid crystallization from silicate liquids having volcanic and/or impact origins. Subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of Martian bright regions at visible and near‐IR wavelengths. Magnetic and phyllosilicate‐poor palagonitic dust from Mauna Kea Volcano is thus a spectral and magnetic analogue for magnetic Martian dust.

Tubular and spheroidal halloysite in pyroclastic deposits in the area of the Roccamonfina volcano (Southern Italy)

Halloysite-bearing weathered pyroclastic deposits of the Roccamonfina volcanic area (Southern Italy), consisting generally of light grey clay masses richer in slightly weathered pumice grains, mottled patches of whitish clayey material and yellowish-brown veins along vertical root channels, were characterised by chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (FT-IR), optical (OM), scanning (SEM) and transmission (TEM) microscopy, electron diffraction (ED) and energy dispersive X-ray analysis (EDXRA). Both tubular and spheroidal forms of halloysite were observed, different parts of the deposits being characterised by a particular morphology. No consistent differences in terms of the chemical and mineralogical composition of the deposit materials were found. However, the chemical composition of the different particle-size clay fractions indicated that less silica, with concomitant relative enrichment in aluminium, and loss of bases characterised the <0.5 μm compared with the 0.5–2.0 μm fraction reflecting their differences in the content of primary minerals. The amounts of Fe, Al and Si extracted by dithionite–citrate–bicarbonate (DCB) and oxalate reagents suggested the presence of short-range-order aluminosilicates but this could not be proved by other physical techniques. X-ray analysis revealed the presence of hydrated (1 nm) and dehydrated (0.7 nm) halloysite, mica, sanidine and plagioclase minerals. TEM/EDXRA analysis of the <0.5 μm clay fraction revealed an amorphous Si-rich phase in the sample containing spheroidal halloysite. The differential X-ray diffraction analysis (DXRD) from untreated and DCB treated yellowish-brown material along with the electron diffraction (ED) of the <0.5 μm clay fraction showed the presence of goethite and ferrihydrite. The various weathered pyroclastic materials showed a major difference in terms of their physical characteristics, particularly in terms of their compactness and porosity/permeability as revealed by microscopic and sub microscopic observations. It is suggested that the different morphological forms of halloysite may result from conditions of growth in the different microenvironments related to variability in physical conditions.

Weathered pumice influence on selected alluvial soil properties in west Nayarit, Mexico

Parent material and pumiceous alluvial soils, located in a tropical region of Mexico, were studied to supply information on soil suitability for agricultural production in the context of sustainable agriculture. In recent alluvial soils, an understanding of how soil characteristics vary with parent material and topography provides a basis for determining land utilization type, land suitability as well as land quality. The main objective of this study was to establish the relationship of soil properties to parent material in west Nayarit, Mexico. Field studies were initiated in 1993 by a request for technical assistance from the Comision Federal de Electricidad. The studied soils were derived from pumice that has been reworked and mixed with detrital material from other sources. We found that such soils have unique physical, chemical and mineralogical characteristics that are rarely found in soils derived from other parent materials. Data for two selected alluvial soil profiles are presented. These soils were developed on Holocene volcanogenic pumiceous alluvial river terraces and river floodplains, under current udic-isohyperthermic soil-climate conditions. The agronomic properties, tillage influences and fertilizer requirements of these soils have been studied extensively. To maximize their productivity and minimize deterioration, proper management must be based on an understanding of the unique physical, chemical and mineralogical properties. Results indicate that such soils have physical properties that provide a good environment for deep rooting and can supply the water necessary for vigorous plant growth. In both soils, water retention at 33 and 1500 kPa, particle surface area, calculated clay, cation exchange capacity, Al exchangeable percentage and P retention, and the occurrence of isotropic coatings on rock fragments and peds tend to increase in the presence of the large amounts of hydrolyzed pumice that are found in the 0.02–2.0 mm fraction. Scanning electron microscope–energy dispersive X-ray analyses demonstrate that the coatings dominantly consist of noncrystalline material, probably allophanic-like material as suggested by the Si/Al molar ratio of 1.0. Selective dissolution analysis reveals that these abundant noncrystalline materials consist of ferrihydrite and allophane with an atomic ratio (Al o−Al p)/Si o of approximately 1.4. Both ferrihydrite and allophane have very large specific surface area and absorptive capacity that make a significant contribution to the overall properties of these soils. X-ray diffraction analysis and transmission electron microscope observation show that the major group of crystalline clay minerals in the upper section of studied soils are tubular and spheroidal halloysite. These soils were classified as Vitrandic Udifluvents according to Soil Taxonomy.

種々のカオリン鉱物の分析電子顕微鏡による化学組成の分析

Chemical compositions of kaolin group minerals, i.e. two kinds of dickite, three kinds of kaolinite and two kinds of halloysite, having various stacking orders and particle shapes, were examined by analytical transmission electron microscope (AEM). Analysed data using the spot mode in probe size of approximately 10 nm were apparently richer in SiO2 than the ideal value of SiO2 obtained by wet chemical analysis except for spheroidal halloysite. On the other hand, analysed chemical data by picture mode for 0.2μm×0.2μm region were in good agreement with ideal value, although those of disordered type kaolinite showed a little SiO2 rich composition. The most probable interpretation for the difference observed between the spot mode and picture mode data was the channeling effect which occurs in the specific orientation between an incident electron beam and a crystal lattice. Furthermore, this effect results in the enhancement of an X-ray intensity for a specific element, although, probability due to the contamination and/or beam damage was also considered. Contents of Fe2O3 in kaolin minerals varied fairly widely among the specimens : Takabatake dickite (poorly ordered) < Red Mountain dickite (well ordered) < Oguni kaolinite (well ordered) < Georgia kaolinite (poorly ordered) < Indonesia halloysite (short tubular) < Motoyama Kibushi clay (disordered) < Ina hallysite (spheroidal).

Towards a general model of quick clay development

Torrance (1983) has recently reviewed factors producing high sensitivity in clayey sediments and proposed a general model for quick clay development. He suggested that the mineralogical requirement for quick clay behaviour to develop is that low activity minerals must predominate in the sediment. This is also the essential mineralogical requirement of the inactive‐particle, short‐range‐bond hypothesis of high sensitivity (Smalley, 1971, 1972a, 1976; Cabrera &amp; Smalley 1973; Smalley, Ross &amp; Whitton, 1980). The predominance of low activity minerals causes most of the interparticle bonds to be of the short‐range variety which allow/promote the‘quick’ behaviour—the transition from solid to liquid. In Canadian or Scandinavian quick clays the short‐range bond requirement is largely met by the abundance of finegrained primary mineral particles. The very sensitive clays involved in the Tauranga landslide in New Zealand (Smalley et al., 1980) owed their sensitivities to their content of inactive spheroidal halloysite particles. By many definitions the Tauranga material is a quick clay and its existence provides us with another window through which to view the quick clay problem. Torrance observed that for a quick clay to develop the sediment must have an open structure with a high void ratio. In a classic Canadian quick clay this structure is obtained by the slow sedimentation of fine particles in the salty Champlain Sea; in the Tauranga soil an open structure is obtained by air‐fall sedimentation of the initial volcanic particles.

Surface Properties of Allophane, Halloysite, and Imogolite

AbstractThe adsorption of sodium, chloride, and phosphate ions by allophane, imogolite, and halloysite has been studied in relation to the surface structure of the mineral samples. The high adsorption of phosphate (&gt;200 μmole/g) and chloride (10–30 meq/100 g at pH 4) by allophane is ascribed to the small particle size of allophane, its high surface area (∼800 m2/g), and the presence at the surface of Al-OH-Al groups and defect sites. In contrast, halloysite has a relatively large particle size and a Si-O-Si surface. Accordingly, the adsorption of phosphate (5–10 μmole/g) and chloride (1 meq/100 g) by halloysite is very much lower as compared with allophane. Phosphate adsorption by halloysite is also related to particle morphology and the number of edge sites. Thus, a sample consisting entirely of spheroidal particles adsorbed only 5 μmole/g at a solution concentration of 1 × 10−4 M, whereas the tubular types of comparable surface area adsorbed 7–10 μmole/g at the same concentration. This is because spheroidal halloysite particles have few, if any, edge sites at which phosphate can adsorb. The relative degree of order and hydration of halloysite, as indicated by infrared spectroscopy, also affects phosphate adsorption. However, this factor is apparently less important than particle morphology and surface structure. Although imogolite also has an Al-OH-Al surface, it contains relatively few defect sites where phosphate can adsorb. Consequently, much less phosphate (120 μmole/g) was adsorbed as compared with allophane.

Origin and nature of halloysite in Ando soils from Towada tephra, Japan

The origin and nature of halloysite in Ando soils from Towada tephra were investigated. These soils were formed from five tephras: Towada-a (1,000 years old), Towada-b (2,000 years old), Chuseri (4,000 years old), Nanbu (8,600 years old) and Ninokura (10,000 years old). Formation of halloysite took place only in the buried soils from Nanbu and Ninokura tephras occurring in an “accumulating zone”, where thicknesses of overburden tephra deposits were mostly 2.5 m or greater and silica enrichment of the clay fractions could occur. The amounts of halloysite were greater in (1) the soils from Ninokura tephra than in those from Nanbu tephra, and greater in (2) the humus horizons as compared to the nonhumus horizons of these same soils. The mean sizes of spheroidal halloysite particles and the ratios of numbers of tubular to spheroidal forms differed with differences in soil horizons and age. High-resolution electron micrographs of glycerol-solvated spheroidal halloysite particles had lattice images of 11 Å due to (001) from the exterior to the interior and had no indications of layer separation. Moreover, the central core of spheroidal halloysite with a diameter of 150 Å showed neither layer structure nor allophane spherules. Results obtained in this study thus indicate that spheroidal and tubular forms of halloysite were formed concurrently in these Ando soils.

Clay Formation from Basic Volcanic Rocks in a Humid Mediterranean Climate

AbstractClay minerals from soils formed on a variety of basic volcanic rocks in the northern Golan Heights, under humid Mediterranean conditions, have been examined mineralogically. The clay from basalt derived soils, mainly Rhodoxeralfs and Haploxeralfs (Red and Brown Mediterranean Soils) contains kaolinite and dioctahedral vermiculite partially interlayered with Al and Fe hydroxy layers. The presence of some illite and quartz in the upper soil horizons is explained by aeolian accretion. A scoria‐derived Rhodoxeralf contains, in addition, some hematite.The clay fraction from Rhodoxeralfs and Haploxeralfs formed on partly palagonitised tuff‐lapilli is composed primarily of b‐axis disordered kaolinite and a poorly crystalline, partly expanding, 2:1 clay mineral, presumed to represent a smectite randomly interlayered with chloritic layers. In the lower horizons of these soils the kaolinite is replaced by a hydrated, spheroidal halloysite. No distinctly amorphous clay minerals were identified. A scheme of an alteration sequence of basic pyroclastics under humid Mediterranean conditions is suggested.

Internal and External Morphology of Tubular and Spheroidal Halloysite Particles

AbstractTubular halloysite from Wagon Wheel Gap, Colorado and spheroidal halloysite from Redwood County, Minnesota were examined by transmission electron microscopy. Clay samples were prepared by the following techniques: drop-mounted suspension on carbon support films; thin sections of clay in Araldite epoxy resin; and carbon-platinum-palladium single-stage replicas.Both types of dehydrated halloysite have interlayer separations between packets of layers. Halloysite tubes are composed of packets as thin as five layers which sometimes reveal a rolled interior configuration in cross-sectional view. Thicker tubes are composed of many layers per packet. Some large tubes appear in cross section as folded packets of layers. The interior morphology of spheroidal halloysite particles is more irregular and the layer structure is more discontinuous than in most tubes. The spheroidal halloysite of this study is characterized by external tangential plates with hexagonal shape suggestive of kaolinite.

Spheroidal Halloysite in a Guatemalan Soil

AbstractMineralogical analyses of clays from two Alotenango soil horizons were made by utilizing transmission and scanning electron microscopy, infrared, X‐ray diffraction, and chemical methods. This report of spheroidal halloysite demonstrates the presence of this mineral form in an area of important volcanic ash‐derived soils where it has not been previously identified. The presence of spheroidal halloysite in Central American volcanic soil and its presence in volcanic soils of Hawaii, Japan, and New Zealand indicate its wide geographic occurrence in soils of volcanic origin. Oblate halloysite spheroids tend to settle preferentially, offering an end‐view along the axis of some particles and correspondingly, reduced 00l X‐ray reflections from portions of layers not parallel to the plane of the powder mount. Halloysite spheroids appear to be composed of roughly concentric layers with occasional interlayer separations. The interior structure suggests inclusion of amorphous cores and interlayers which appear to be removed by 0.5N NaOH. The exterior layers often retain a shell‐like appearance after NaOH treatment. The apparent association of spheroidal halloysite and allophane interlayers suggests that the crystalline component forms alternately with the amorphous one. The crystalline exterior may protect amorphous interior material from rapid alteration and cause allophane to persist in a soil where minerals representing more advanced stages of weathering have accumulated.