Types Of Clay Minerals Research Articles

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

A Review of Empirical Models of Sorption Isotherms of Hydrophobic Contaminants

Renewed focus on empirical models of sorption isotherms of hydrophobic organic contaminants (HOCs) onto mineral surfaces and soil components is required because of the importance attached to numerous pollutants released into the environment. This examines the various models and isotherms with their assumptions by different scholars on the contribution of sorption of contaminants onto clay mineral sorbents and soil organic matter with the possible ways of prevention of environmental contamination by HOCs. Literature indicated that empirical models and isotherms have been used to ascertain several surfaces that can be sorbed by hydrophobic organic contaminants. These models also show that soils can retain HOCs even at low soil organic levels and the extent depends on the structure of the pollutant type and concentration of clay minerals in the sorbent. It also revealed the important role played by soil organic carbon in the sorption of contaminants onto soils and how it is strongly affected by the nature and structure of the organic soil matter. Contamination by different pollutants required a renewed approach in the context of the sorption of organic pollutants onto clay minerals from aqueous and non-aqueous solutions.

Soil water repellency characteristic curve of Spolic Technosols from the region of Maritsa-Iztok coal mine in Bulgaria

Soil water repellency is phenomenon which is caused by compounds of organic origin, type of clay minerals and wetting/drying cycles. Hydrophobicity is usually characterized by a great spatial and temporal variability, especially in mine spoils where different types of overburden materials are mixed with coal particles and other waste products. The aim of this study was to investigate the changes of hydrophobicity with soil moisture content of Heavy Clay textured Spolic Technosols in the region of Maritsa-Iztok open cast coal mine. The sampling was done in a stubble field at 8 points from two soil depths 10–15 cm and 30–35 cm. The samples were analyzed for particle size distribution, total organic carbon content, soil bulk density, soil moisture content at field sampling, soil particle density, soil moisture content and water-drop-penetration-time (WDPT) at different matric potentials (SWRCC). The irregular presence of coal particles and different overburden sediments lead to spatial variability of studied properties, especially of total organic carbon content. In depth the average clay content, organic carbon content, water retention properties and soil water repellency (SWR) increased and correspondingly the density properties decreased. The distribution of SWR classes of the studied samples at the applied suctions during the drying process showed that the hydrophilicity of all samples at saturation persisted at suction pF 1.0 in 73% of the samples Most of the samples at suctions pF 1.7 and pF 2.0 were with slight and strong water repellency, but still there were hydrophilic samples 27% and 18%, correspondingly. At pF 2.5, which is often accepted as field capacity of fine textured soils, all samples were water repellent. The further drainage of the samples at pF >3.3 led to domination of extreme SWR and above pF3.7 all samples were extremely water repellent. Besides the unfavorable consequences of water repellency, the dry hydrophobic topsoil at the time of sampling formed a capillary barrier that reduced the evaporation and led to nearly 3 times higher water content stored in the subsoil.

STUDY OF THE MUTUAL EFFECT OF PHOSPHORUS-CONTAINING FERTILIZERS AND CLAY MINERALS OF ALUMINOSILICATE TYPE ON THE PRODUCTIVITY OF AGRICULTURAL PRODUCTS AND THE ECOLOGICAL CONDITION OF BROWN-BROWN SOILS

The input of phosphorus-containing type clay minerals into the fertile soil, on the background of mineral fertilizers of the aluminum-silicate type, significantly improves the water-physical and agrochemical characteristics of the soil and improves its ecological condition. The both presence of clay minerals and mineral fertilizers in the soil creates the prerequisites for improving soil fertility due to the effect on mobile phosphorus

Application of sodium dodecyl sulfate intercalated Co[sbnd]Al LDH composite materials (RGO/PDA/SDS-LDH) in membrane separation

Layered double hydroxides (LDHs) is a typical type of anionic clay minerals. In this study, an SDS-LDH with sodium dodecyl sulfate (SDS) intercalation was prepared by the ion exchange method, and the modified SDS-LDH was successfully combined with graphene oxide (GO). In the presence of dopamine, partial reduction of GO to reduced graphene oxide (RGO). RGO/PDA/SDS-LDH (RPS) composite material was prepared successfully and used in the field of membrane separation. The RPS-2 composite membrane combines the advantages of GO and SDS-LDH, which can increase GO flux while maintaining a high rejection rate. The flux was increased from 10.21 L·m−2h−1bar−1 of GO to 79.24 L·m−2h−1bar−1 of RPS-2, and the rejection rate of various dyes was above 97%. The rejection rate of methylene blue (MB) 97.34% was maintained after 10 cycles, and its flux loss rate is only 45.32%. The composite membrane had good stability under different pH conditions, which provides a basis for the practical application of the membrane.

Inactivation of bacteria using Fe3+-loaded montmorillonite

Water treatment in developing countries must treat pathogenic microorganisms such as Escherichia coli bacteria using locally available materials. In this study, a typical clay mineral, montmorillonite (MT), was loaded with Fe(III), which has bactericidal properties. Then, the Fe3+-loaded montmorillonite (Fe3+-MT) was used to treat pure E. coli cultures, secondary effluents, and wastewater. Experimental data showed that Na+-MT could not eliminate viable bacteria. On the other hand, using the colony count method to evaluate treatment efficiency, Fe3+-MT was found to be effective for treating E. coli, coliforms, and standard place count bacteria. However, the efficiency differed depending on the type of bacteria; Fe3+-MT treated E. coli and coliform bacteria with approximately equal efficiency and had a lesser effect on the overall bacterial assemblage. The effect of Fe3+-MT also depended on the water quality: a greater treatment efficiency was found in wastewater than in secondary effluents. Additionally, this study investigated the treatment mechanism of Fe3+-MT by measuring the number of viable bacteria and total bacteria using a fluorescent staining method. This analysis showed that the number of viable bacteria decreased, unlike the total number of bacteria, demonstrating that there was an increase in the number of dead bacteria. This confirmed that Fe3+-MT effectively treats bacteria through inactivation.

Control of paddy soil redox condition on gross and net ammonium fixation and defixation

Abiotic fixation and defixation of ammonium (NH4+) in silicate interlayers are common processes in paddy soils, owing to their often high levels of 2:1 type clay minerals. Fixed NH4+ hence forms a buffer during the supply and loss of plant-available N. The soil redox potential (Eh) is suspected to influence NH4+ (de)fixation by its impact on the negative charge of Fe3+-containing clay minerals, yet experimental confirmations are scarce. We examined the effect of a fluctuating or generally increased Eh on dynamics of NH4+ (de)fixation in a Bangladeshi paddy soil (total N: 1.9 g kg−1 | CEC: 43 cmol kg−1) during two incubation experiments. In those, we either 15N-labelled the fixed NH4+ pool (with initially 87 mg kg−1 exchangeable versus 393 mg kg−1 fixed NH4+-N) or the exchangeable pool (with initially 141 mg kg−1 exchangeable versus 249 mg kg−1 fixed NH4+-N), and this under three Eh-controlling treatments: continuous flooding (CF), CF with extra MnO2 added (3.5 g kg−1 Mn4+) (CF-MnO2), and alternate wetting and drying (AWD). The CF treatment overall led to somewhat higher net NH4+ fixation than AWD and, less clearly, also compared to the CF-MnO2 treatment, resulting from higher gross NH4+ fixation as well as lower gross defixation. These fluxes always led to a dynamic equilibrium between the exchangeable and fixed NH4+ pool within a few days of incubation, and this equilibrium was the same for both experiments but depended on the Eh treatment. However, by altering other NH4+ transformation processes, Eh treatments also indirectly impacted NH4+ (de)fixation fluxes, for which the equilibrium ratio between exchangeable versus fixed NH4+ turns out to be the determining factor.

Compositional Control on Shale Pore Structure Characteristics across a Maturation Gradient: Insights from the Devonian New Albany Shale and Marcellus Shale in the Eastern United States

The pore structure characteristics of shales are controlled by their mineralogical and organic matter (OM) compositions. However, the contributions by different components in shales at varying thermal maturities remain poorly understood. In this study, Devonian New Albany Shale and Marcellus Shale samples spanning a thermal maturity from marginally mature (vitrinite reflectance Ro 0.55%) to post-mature (Ro 2.41%) were selected to study the control of the composition on the pore structure properties of shales at different stages of thermal maturation. Scanning electron microscopy (SEM) imaging was used to examine the pore types in shales, and low-pressure N2 and CO2 adsorption analyses were used to quantitatively characterize the mesopore and micropore characteristics of bulk shales and major components in shales. The results show that matrix-associated pores including interparticle pores between silt-sized mineral grains, phyllosilicate framework pores, and intraparticle pores within mineral grains exist in all samples but become less common with increasing maturity, which is likely caused by the elevated compaction, cementation, and occlusion with bitumen. Secondary organic pores were not observed by SEM at marginal maturity but were detected in the condensate-wet gas and dry gas windows, with more organic pores in the dry gas window. At marginal maturity, OM has large amounts of mesopores and micropores, as demonstrated by low-pressure N2 and CO2 adsorption analyses of OM isolated from shales, even though no OM-hosted pores were observed by SEM. With increasing thermal maturity, the mesopore and micropore specific surface areas (SSAs) of OM increase and make greater contributions to the pore structure properties of bulk shales. The mesopore and micropore properties of shales are controlled by the OM content and maturity as well as by the clay mineral type and content, and they can be estimated from the contribution of each component at different stages of thermal maturation. Accurate evaluation of the pore volume and SSA of shales will have important implications for assessing gas adsorption and transport in shales.

Mineralogical and Geochemiccal Assessment of Edda Clays for Possible Use in the Ceramics Industry,Afikpo Sub-Basin,Nigeria

Clay samples from selected part of Edda were analyzed to identify the clay mineral types present, their chemical and physical properties with a view to appraising their industrial suitability as ceramic materials. The mineralogical and geochemical analyses were done using the principles of X-Ray diffraction and X-ray fluorescence respectively. A total of seven clay samples were used for the study, other tests such as plasticity, bulk density, shrinkage, loss on ignition (LOI) and water absorption capacity was carried out to determine the amount of water absorbed under specified conditions. The basic industrial properties assessment showed that more than 70% of the clays are fine-grained. The clays exhibited low to moderate plasticity, moderate shrinkage and bulk density, low to moderate values of both loss on ignition and water absorption capacity. The clays are buff to yellowish in colour. The results of x-ray fluorescence revealed that the mean concentration of major oxide in the clays is shown as follows: SiO2 (62.78%), Al2O3 (20.25%), total Fe (6.09%), CaO (0.56%), MgO (3.21%), Na2O (0.47%), K2O, (1.44%) and TiO2 (0.52%). The samples have high silica content, low alumina and low oxide content. The results of x-ray diffraction revealed that kaolinite is the dominant clay mineral with illite and montmorillonite occurring in subordinate amounts, while quartz and feldspar are the non-clay components present. The characteristics of the clays for each parameter were compared with industrial standards. These properties are appropriate for the Afikpo clays to be useful in the manufacturing of ceramics. However, since the silica content of the clays is high further beneficiation is recommended.

Interfacial reaction between organic acids and iron-containing clay minerals: Hydroxyl radical generation and phenolic compounds degradation

Reactive oxygen species, especially hydroxyl radicals (OH), exert a distinguished role in the transformation of contaminants, and their in-situ generation attracts wide attentions in environmental and geochemical areas. The present work explored the potential formation of OH during the interactions between iron-containing clay minerals and environmentally prevalent organic acids in dark environments. The results demonstrated that the accumulative OH concentrations were related to the solution pH, the types of clay minerals, and the nature of organic acid species. At pH 5.5, 1.2– 15.2 times of OH were generated from the reduction of Na-nontronite-2 (Na-NAu-2) compared with other clay minerals in the presence of ascorbic acid (AA) at 144 h. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) analyses indicated that Fe(III) was reduced to Fe(II) by AA during OH formation. Meanwhile, chemical probe tests coupled with quenching experiments confirmed the generation of H2O2 and superoxide radical (O2–), which participated in the formation of OH. The produced OH/O2– can transform 68.4%, 86.4%, and 50.1% of phenol, p-nitrophenol, and 2,4-dichlorophenol within 168 h in AA-Na-NAu-2 suspension, respectively. This work provides valuable insights into OH production in the mutual interaction between organic acids and iron-bearing clays, which is helpful for the development of a new method for removing organic pollutants from contaminated water and soil environments.

Sorption behavior of cesium on silt and clay soil fractions

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 μm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

Adsorption and desorption of Thallium(I) in soils: The predominant contribution by clay minerals

Thallium (Tl) is a highly toxic environmental contaminant. To understand the mechanism controlling the mobility and availability of Tl in soil, the adsorption and desorption of Tl(I) were evaluated for six soils. The maximum Tl adsorption capacities of the soils ranged from 6.9 to 244.5 mmol kg−1. The corresponding Tl LIII-edge X-ray absorption near-edge structure (XANES) data revealed that illite, vermiculite, and smectite are the preferential soil constituents for adsorbing Tl(I). Tl(I) adsorption by the soils was reversible in the low Tl adsorption regime and exhibited various degrees of hysteresis as the amount of absorbed Tl increased. The Tl(I) adsorption and extent of adsorption reversibility were mainly dependent on the type and content of clay minerals and exchangeable cations in different soils. Despite high Tl(I) adsorption by the soils, the reversibility of Tl(I) adsorption may result in relatively high mobility and availability of Tl(I) in soils, leading to high environmental risk. Ignoring the reversibility of Tl adsorption could lead to an erroneous prediction of the mobility and availability of Tl in soils and a significant underestimation of the environmental risk posed by Tl in the environment.

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Impact of Clay mineral type on sandstone permeability based on field investigations: case study on Labuan island, Malaysia

Permeability is a petrophysical parameter that can indicate the economical value of sandstone as a hydrocarbon reservoir. In presence of Clay minerals in sandstone composition, permeability can be affected significantly according to the Clay mineral type. Therefore, understanding the impact of Clay on the permeability of sandstone has a big importance in scientific research and industry as well. Although well-logs can provide very good data quality, it is not cost-effective as a preliminary tool. However, field investigations and observations are basic tools to collect valuable data in a short time at a very low cost. In this paper, 30 intervals from 10 outcrops in Labuan island were selected to be described and investigated in the field using air permeameter and portable gamma-ray spectrometer with no additional lab investigations except 3 thin-sections for validation. Tinyperm II was used to determine the permeability, while gamma-ray spectrometer was used for Clay minerals typing. Results of lithofacies, permeability, and gamma-ray have shown a lack of relation between facies and permeability in the selected outcrops while showing a significant impact of the authigenic Clay minerals on permeability according to their types and morphologies. This paper can provide a good reference for preliminary reservoir field studies.

Morphological and Spectral Diversity of the Clay-Bearing Unit at the ExoMars Landing Site Oxia Planum.

The European Space Agency and Roscosmos' ExoMars rover mission, which is planned to land in the Oxia Planum region, will be dedicated to exobiology studies at the surface and subsurface of Mars. Oxia Planum is a clay-bearing site that has preserved evidence of long-term interaction with water during the Noachian era. Fe/Mg-rich phyllosilicates have previously been shown to occur extensively throughout the landing area. Here, we analyze data from the High Resolution Imaging Science Experiment (HiRISE) and from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments onboard NASA's Mars Reconnaissance Orbiter and the Colour and Stereo Surface Imaging System (CaSSIS) onboard ESA's Trace Gas Orbiter to characterize, at a high spatial resolution, the morphological and spectral variability of Oxia Planum's surface deposits. Two main types of bedrocks are identified within the clay-bearing, fractured unit observed throughout the landing site: (1) an orange type in HiRISE correlated with the strongest detections of secondary minerals (dominated by Fe/Mg-rich clay minerals) with, in some locations, an additional spectral absorption near 2.5 μm, suggesting the mixture with an additional mineral, plausibly carbonate or another type of clay mineral; (2) a more bluish bedrock associated with weaker detections of secondary minerals, which exhibits at certain locations a ∼1 μm broad absorption feature consistent with olivine. Coanalysis of the same terrains with the recently acquired CaSSIS images confirms the variability in the color and spectral properties of the fractured unit. Of interest for the ExoMars mission, both types of bedrocks are extensively outcropping in the Oxia Planum region, and the one corresponding to the most intense spectral signals of clay minerals (the primary scientific target) is well exposed within the landing area, including near its center.

A new model for soil water vapor sorption isotherms considering adsorption and condensation

AbstractA new model, which was based on the Do and Do (2000) model, was developed to describe soil water vapor sorption isotherms (SWSIs) including both adsorption and condensation processes. The model performance was evaluated using measured SWSIs of 33 soil samples with a wide range of clay contents (0.08–0.72 g g−1), clay mineralogy (montmorillonite, kaolinite, and mixed clay samples), and organic C contents (0.001–0.070 g g−1). The new model produced satisfactory fits to measured SWSIs, with the mean relative percentage deviation modulus less than 6.2%. For a given clay mineral type, the adsorption sites and condensation capacity increased with increasing clay content. At a given clay content, the number of adsorption sites was in the order of montmorillonitic samples (ML)&gt;mixed clay samples (MX)&gt;kaolinitic samples (KA), and the condensation capacities of ML and MX were lower than that of KA. For soils with low clay content (&lt;0.12 g g−1) and similar clay mineralogy, the adsorption sites and condensation capacities were positively related to organic C. The model parameter S0 had the potential for deriving cation exchange capacity, specific surface area, and clay content. The C/S0 values could potentially be used as a proxy of the dominant clay mineral type in a sample.

Determination of slope susceptibility in hydrothermally altered rocks region with a case study in wonotirto district, blitar regency, east java province, indonesia

The significance of slope susceptibility study in hydrothermally altered area is to determine which area that geological landslide hazard is potentially occurred. This study is aimed to develop a geological hazard map based on overlaying of slope data and types of hydrothermal alteration, with the case study in Wonotirto district, Blitar regency, East Java province. Wonotirto district lies on a high topographic terrain covered up by hydrothermally altered volcanic rocks. To achieve these aims, this study was performed a suite of research methods, which are conducted through four work stages including geological mapping and slope observation, sampling, laboratory analysis and data interpretation. Slope data measurement is based on DEM data and verified in the field. Laboratory analyses consist of petrography, XRD (X-Ray Diffraction) and geomechanical properties analysis for the representative samples. The hydrothermal alteration occurred in study area consists of 4 (four) alteration types i.e. silicification, advanced argillic, argillic and propylitic alteration. Overlaying of slope data, geomechanical properties of rocks and the provided alteration map by using ArcGIS software leads the determination of slope susceptibility of the area. The area covered by extensive argillic-altered rocks shows highest slope susceptibility. On the map, the high slope susceptibility places on the northernmost sector of the study area. Meanwhile, the moderate slope susceptibility area occupies the central part of the map and the southernmost part has the lower slope susceptibility. Argillic altered rocks contain abundant clay minerals such as smectite and illite. Smectite, particularly, is a clay mineral type which has high swelling potential index. The abundantly presence of the clay minerals in the altered rocks may trigger the formation of geological landslide failure/hazard in the region.

Permeability and porosity modelling for resedimented mudrocks – Applications for compaction dominated mudrock systems

Mudrocks have complex petrophysical properties due, in part, to their very fine grain size and the associated high specific surface area (m2/g) and cation exchange capacity (CEC, meq/g). The role of the cation exchange capacity and its associated bound water must be included to account for mudrock electrical, transport, and mechanical properties. A widely varying set of samples from the deep water Gulf of Mexico Miocene section, the arctic seafloor, the Pierre Shale, and Brazos River sand (used for varying sand content) were resedimented to study the effects of these variations on compaction and permeability. The mudrocks were characterized in terms of CEC, clay mineral content, bulk mineralogy, and particle size distribution. Resedimentation techniques were employed to measure the mudrock properties under controlled conditions i.e. slurries were made with known clay mineral type, bulk mineralogy, particle size distribution, CEC, and pore fluid salinity, and subsequently compacted in an oedometer cell.The measured permeabilities were found to be strongly dependent on the clay mineral CEC and on initial pore fluid salinity. Two models were developed to explain the variation in measured permeability: a modified Carman-Kozeny model and a staged differential effective medium model (SDEM). The Carman-Kozeny model fits the permeability data to within a factor of three but underestimates the stress dependence. The SDEM model includes the effects of both bound water saturation and porosity on fluid flow. The model was also able to estimate permeability for all the different mudrocks to within a factor of three with an improved match to the stress dependence. These two models were also successfully tested using previously published permeability data for both resedimented and intact Boston Blue clay samples.A compaction model for porosity was also developed and applied to published data for artificial mixtures of smectite and kaolinite. The model predicts the stress dependent porosity of the resedimented clays to within four percent error. It is then extended to incorporate the influence of the inclusion of sand sized material and applied to our resedimentation data and previously published Boston Blue Clay data. The required inputs for the model include the weight fraction of non-clay sized material, and the cation exchange capacity (CEC, meq/gram). No consistent salinity dependence was observed for compaction.

Study on Volume Reduction of Cesium Contaminated Soil by High Gradient Magnetic Separation: Design of Magnetic Filters

The superconducting magnetic separation was examined to reduce the volume of cesium contaminated soil by the Fukushima Daiichi nuclear power plant accident. By using superconducting high gradient magnetic separation, silt and clay with high radioactive concentration due to the large particle surface area per unit mass can be further separated into high-dose 2:1 type and low-dose 1:1 type clay minerals selectively. Here, we examined filter conditions to improve the magnetic separation performance in farmland soil that is rich in organic matter. The results of magnetic separation of uncontaminated soil suggested that the separation selectivity of 1:1 and 2:1 type clay minerals was larger with the filters with smaller wire diameter. On the other hand, it was found that it was difficult to magnetically separate 0-20 μm particles even with the filters with small wire diameter and high selectivity. To solve this problem, magnetic separation was performed under the same conditions on actual contaminated soil that was highly classified into 0-20 μm and 20-75 μm particles. As the result, it was found that the radioactivity can be further reduced by removed high-dose 0-20 μm particles and targeting the 20-75 μm particles.

Physical, chemical, and mineralogical attributes and organic fractions of biogenic aggregates of earthworms and toposequence of Inceptisol in semi-arid region

ABSTRACT Earthworms are known to improve soil fertility by altering the physicochemical properties of soil. However, the changes in properties of biogenic aggregates (produced by earthworms) in regions with different vegetation covers and soils of Inceptisol toposequence in the semi-arid region have not been studied. The objective of this work was to determine the variations of the physical, chemical, and mineralogical attributes and organic fractions of biogenic aggregates of earthworms under different vegetation covers and compare them to an Inceptisol toposequence in the semi-arid region of Pernambuco State, Brazil. For this study, four Inceptisol soil profiles were selected. The sampled points were P1-upper; P2-middle third; P3-middle third; and P4-lower slope, and the soils were collected at a depth of 0-0.20 m. The biogenic aggregates were found in the P3 samples collected from three areas with different vegetation covers: an area with mesquite tree vegetation (Prosopis juliflora [Sw] D.C.); an area with neem tree vegetation (Azadirachta indica A. Juss); and an area with forage palm and mesquite tree vegetation (Opuntia sp. and Nopalea sp.). Results indicate that the biogenic aggregates were in the form of irregular blocks with a size greater than 40 mm. As compared to Inceptisol samples, these aggregates tended to select particles of smaller diameter and exhibited higher concentrations of clay minerals. The chemical and organic fraction analysis revealed that the aggregates exhibited higher Ca2+, total organic carbon (TOC), labile and humic substances, regardless of the vegetation cover. The mineralogical analysis revealed that the action of earthworms did not change the quantity or type of clay minerals.