Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. Diversity also characterizes their chemical composition, cation exchange capacity and potassium selectivity. This review summarizes the extensive but scattered literature on halloysite, from its natural occurrence, through its crystal structure, chemical and morphological diversity, to its reactivity toward organic compounds, ions and salts, involving the various methods of differentiating halloysite from kaolinite. No unique test seems to be ideal to distinguish these 1:1 clay minerals, especially in soils. The occurrence of 2:1 phyllosilicate contaminants appears, so far, to provide the best explanation for the high charge and potassium selectivity of halloysite. Yet, hydration properties of the mineral probably play a major role in ion sorption. Clear trends seem to relate particle morphology and structural Fe. However, future work is required to understand the possible mechanisms linking chemical, morphological, hydration and charge properties of halloysite.

Halloysite clay minerals — a review

Clay minerals, recently discovered to be widespread in Mars’s Noachian terrains, indicate long-duration interaction between water and rock over 3.7 billion years ago. Analysis of how they formed should indicate what environmental conditions prevailed on early Mars. If clays formed near the surface by weathering, as is common on Earth, their presence would indicate past surface conditions warmer and wetter than at present. However, available data instead indicate substantial Martian clay formation by hydrothermal groundwater circulation and a Noachian rock record dominated by evidence of subsurface waters. Cold, arid conditions with only transient surface water may have characterized Mars’s surface for over 4 billion years, since the early-Noachian period, and the longest-duration aqueous, potentially habitable environments may have been in the subsurface.

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Subsurface water and clay mineral formation during the early history of Mars

The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Mineralogie, l'Eau, les Glaces, et l'Activite (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near-infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg-rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high-resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low-grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JE003339

Identification of hydrated silicate minerals on Mars using MRO‐CRISM: Geologic context near Nili Fossae and implications for aqueous alteration

Hydration of the <1 μm size fraction of SWy-1 source clay (low-charge montmorillonite) was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Li-, Na-, K-, Mg-, Ca-, and Sr-saturated specimens. The quantitative description of smectite hydration, based on the relative proportions of different layer types derived from the fitting of experimental XRD patterns, was consistent with previous reports of smectite hydration. However, the coexistence of smectite layer types exhibiting contrasting hydration states was systematically observed, and heterogeneity rather than homogeneity seems to be the rule for smectite hydration. This heterogeneity can be characterized qualitatively using the standard deviation of the departure from rationality of the 00 l reflection series (ξ), which is systematically larger than 0.4 A when the prevailing layer type accounts for ~70% or less of the total layers (~25% of XRD patterns examined). In addition, hydration heterogeneities are not distributed randomly within smectite crystallites, and models describing these complex structures involve two distinct contributions, each containing different layer types that are interstratifed randomly. As a result, the different layer types are partially segregated in the sample. However, these two contributions do not imply the actual presence of two populations of particles in the sample.

XRD profile modeling also has allowed the refinement of structural parameters, such as the location of interlayer species and the layer thickness corresponding to the different layer types, for all interlayer cations and RH values. From the observed dependence of the latter parameter on the cation ionic potential ( v / r; v = cation valency and r = ionic radius) and on RH, the following equations were derived:

\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Layer\ thickness\ (1W)\ =\ 12.556\ +\ 0.3525\ {\times}\ ({\nu}/\mathit{r}\ {-}\ 0.241)\ {\times}\ ({\nu}\ {\times}\ RH\ {-}\ 0.979)\] \end{document} 

\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Layer\ thickness\ (2W)\ =\ 15.592\ +\ 0.6472\ {\times}\ ({\nu}/\mathit{r}\ {-}\ 0.839)\ {\times}\ ({\nu}\ {\times}\ RH\ {-}\ 1.412)\] \end{document} 

which allow the quantification of the increase of layer thickness with increasing RH for both 1W (one water) and 2W (two water) layers. In addition, for 2W layers, interlayer H2O molecules are probably distributed as a unique plane on each side of the central interlayer cation. This plane of H2O molecules is located at ~1.20 A from the central interlayer cation along the c* axis.

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Investigation of smectite hydration properties by modeling experimental X-ray diffraction patterns: Part I. Montmorillonite hydration properties

Human societies have, in all ages, modified the original form of metals and metalloids in their living environment for their survival and technical development. In many cases, these anthropogenic activities have resulted in the release into the environment of contaminants that pose a threat to ecosystems and public health. Examples of local and global pollution are legion worldwide, and the reader of the environmental science literature is forever faced with ever more alarming reports on hazards due to toxic metals. For example, extensive mining and associated industrial activities have introduced large amounts of metal contaminants in nature at the local, but also global, scale since anthropogenic metals are detected in remote areas including Greenland ice (Boutron et al. 1991). Industrialized countries have countless polluted sites, and the major consequence in terms of contamination by heavy metals are areas of wasteland and sources of acid and metal-rich runoff from tailings piles and waste-rock heaps, and the subsequent pollution of coastal areas. Water supplies in many areas of many countries are also extensively polluted or threatened by high concentration of metal(loid)s, sometimes from natural sources, but most often from the activities of humans (Smedley and Kinniburgh 2002). Pollution of ground and surface waters, and hence of lands, by arsenic from alluvial aquifers in the Bengal Delta plain and in Vietnam are probably the two most catastrophic actual examples of the second type, where a modification of the chemistry of deep sediment layers by intensive well drillings and pumping of drinking water has led to vast arsenic remobilization and poisoning of ecosystems (Chatterjee et al. 1995; Nickson et al. 1998; Berg et al. 2001).

Soils and sediments, being at the interface between the geosphere, the atmosphere, the biosphere and the hydrosphere, represent the major sinks for anthropogenic metals released to …

Quantitative Speciation of Heavy Metals in Soils and Sediments by Synchrotron X-ray Techniques

The diagenetic evolution of kaolin and illitic minerals in sandstones is described here. The structural characterization of these minerals, the possible reaction pathways leading to their crystallization, and the origin of the fluids involved are discussed specifically.

While early precipitation of kaolinite is in general related to flushing by meteoric waters, subsequent diagenetic kaolinite-to-dickite transformation probably results from invasion by acidic fluids of organic origin. Dickite is the stable polytype in most sandstone formations and the kaolinite-to-dickite conversion is kinetically controlled.

The conventional model of kaolin illitization, assuming a thermodynamic control in a closed system, is discussed and compared to an alternative model in which illitization of kaolin is not coupled to dissolution of K-feldspar (Berger et al. , 1997). In the latter model, illite crystallization at the expense of kaolin implies that an energy barrier is overcome either by an increased K+/H+ activity ratio in solution or by a considerable temperature increase.

Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review

The SEM, XRD, FTIR and DTA analyses of different size-fractions of clay material from sandstone reservoirs which have experienced a large range of burial conditions have been used to examine the different steps of the depth-related kaolinite-dickite reaction. Dickite progressively replaced kaolinite within a range of burial depths estimated between about 2500 m and 5000 m. The kaolinite-to-dickite reaction proceeds by gradual structural changes concomitant to crystal coarsening and change from booklet to blocky morphology. The crystallization of dickite proceeds by two distinct paths: (1) Accretion of new material from either dissolution of smaller unstable kaolinite crystals and/or detrital minerals (chiefly feldspars), on early-formed coarser metastable kaolinite crystals which exert extended morphological control on the growing crystals. (2) Neoformation of ordered dickite which will continue to grow by a dissolution-crystallization process. The kaolinite-to- dickite reaction is kinetically controlled and anomalies in the kaolinite/dickite ratio observed in certain sandstone reservoirs may be used to assess the timing of invasion by hydrocarbons.

Kaolinite-to-dickite reaction in sandstone reservoirs

Low-temperature chlorites formed in diagenetic to low-grade metamorphic environments generally have greater Si contents and larger numbers of octahedral vacancies, and smaller Fe+Mg contents than higher-grade metamorphic chlorites. The compositional variations are characterized approximately by four end-member components: Al-free trioctahedral chlorite, chamosite, corundophilite, and sudoite. The solid solution is considered to be a random mix of cations and vacancies in the octahedral sites. Using the compositions of chlorites from Niger, Rouez, and Saint Martin diagenetic-hydrothermal series, a new, more convenient geothermometer, applicable to low-T chlorites is proposed and comparison made with geothermometers proposed previously. The chlorites studied contain appreciable amounts of Fe(III) (>14% of the total Fe), determined by Mossbauer spectroscopy. The calculations under which all Fe was regarded as ferrous gave considerable overestimates for the formation temperature, irrespective of the geothermometer used. This problem was reduced by taking into account the presence of Fe(III) in the octahedral sites. The geothermometer from this study gave more reasonable estimates than the geothermometers proposed by Walshe (1986) and Vidal et al. (2001), particularly in the case of the Niger chlorites which crystallized in the lowest-temperature conditions. The ordered-site substitution model of solid solution developed by Vidal et al. (2001) predicted satisfactorily the formation temperature of the Rouez chlorites and of some of the Saint Martin chlorites, suggesting that the chlorite compositions are controlled by the ${\rm{Si}}\square R_{ - 2}^{2 + }$
 exchange at low-T conditions while they are controlled by Tschermak exchange at higher temperatures. The decreasing number of vacancies with temperature are poorer in Fe-rich than in Fe-poor chlorites. Furthermore, the ordered-site occupation of cations and vacancies in trioctahedral chlorite occurs concomitantly with the compositional changes ruled by increasing temperature conditions.

Application of chemical geothermometry to low-temperature trioctahedral chlorites

This present study provides an overview of the clay-mineral reactions involved in the chloritization process in a mixed-layer mineral series, and focuses on the properties of the resulting low-temperature chlorites (formed at <220°C) in diagenetic and hydrothermal systems. According to the literature, most chlorite species occurring in low-temperature geological systems are derived from specific clay precursors except for direct precipitates from solution in veins. In addition, three main types of clay-mineral series have been associated with these chloritization processes: saponite-to-chlorite, berthierine-to-chlorite and kaolinite-to-sudoite reactions. The conversion of saponite to chlorite results in the most common sequence of trioctahedral clay minerals related to the occurrence of Mg-Fe trioctahedral chlorite in a wide variety of hydrothermal and diagenetic to very low-grade metamorphism environments. Two models were proposed in the literature to describe the saponite-to-chlorite conversion through corrensite. The first model is a continuous transition model based on solid-state transformation (SST) mechanisms and is valid in rock-dominated systems (closed micro-systems with very low fluid-rock ratios). The second model is a stepwise transition model based on dissolution-crystallization mechanisms (DC) and is efficient in fluid-dominated systems (open systems with high fluid-rock ratio). The berthierine to Fe-chlorite transition results in a sequence of trioctahedral phases which are related to chloritization processes in iron-rich and reducing environments. This transformation is a cell-preserved phase transition dominated by a SST mechanism that operates simultaneously in different domains of the parental mineral and may be considered as a polymorphic mineral reaction. Finally, the conversion of kaolinite to sudoite (Al-Mg di-trioctahedral chlorite) has not been documented like the other two aforementioned conversion series. Despite the scarcity of detailed investigations, the conversion of kaolinite to sudoite through tosudite is considered a stepwise mineral reaction that is dominated by a DC mechanism. From a compilation of literature data, it appears that several parameters of hydrothermal and diagenetic chlorites differ, including the minimal temperature, the textural and structural characteristics and the extents of compositional fields. In hydrothermal systems, discrete chlorite occurs at a minimal temperature near 200°C, regardless of its chemical composition. In diagenetic systems, discrete chlorite occurs at minimal temperatures that vary according to its crystal chemistry (100–120°C for Mg-chlorite as opposed to 40–120°C for Fe chlorite). The strong discrepancy between the lowest temperature at which Mg- and Fe-chlorite form in buried sediments and in geothermal systems should result from drastically different heating rates, heat-flow conditions and tectonism between basins at passive margins and geothermal systems at active margins. The morphology, structure and compositional fields of the diagenetic Fe-rich chlorite may have been inherited from those of the berthierine precursor. All of the chlorite species formed through the DC mechanism have good geothermometry potential. However, the SST mechanism in which berthierine is transformed into chlorite could have unexplored consequences regarding the use of the chemistry (including stable isotope composition) of diagenetic Fe-chlorite for reconstructing the burial history of sediments. Further investigations regarding the formation mechanisms of mixed-layer minerals are required to provide us with insight to understand the chloritization process in low-temperature geological systems.

Chlorite and chloritization processes through mixed-layer mineral series in low-temperature geological systems – a review

This paper describes the diagenetic evolution of clay minerals in the Rotliegend sandstone reservoir under contrasting burial histories in the Broad Fourteens basin (Dutch sector, Southern North Sea). The diagenetic modifications affecting the crystal structure of clay minerals (both kaolin-group and illitic minerals) were studied using X-ray diffraction (XRD). The XRD study includes oriented and random mounts of various size fractions, numerical processing (decomposition) of XRD profiles, and simulation of one-dimensional and three-dimensional XRD patterns. Petrographic observations, differential thermal analysis, K/Ar geochronology, and geochemical considerations complement the XRD study and allow determination of the sequence of mineral crystallization and the morphological evoluti n of clay minerals and place further constraints on the absolute timing of diagenetic events and on the nature of the fluids responsible for clay-mineral crystallization. From deposition time ( 275 Ma) to the Kimmerian orogeny ( 155 Ma), crystallization of kaolinite at the expense of K-feldspars was favored by acid fluids from the underlying Carboniferous Coal Measures source rocks; kaolinite crystallization is followed by a steady kaolinite-to-dickite transformation affecting both the structure and the morphology of kaolin-group minerals. The structural characteristics of kaolin-group minerals are related to the burial history of the sediments prior to the Kimmerian orogeny. During the Kimmerian orogeny, rapid illitization of kaolin-group minerals was favored both by increased heat flow in the sedimentary pile and by widespread presence of faults, which permitted significant fluid flow probably from the Zechstein Formation. The morphological and structural characteristics of illitic minerals, i.e., illite content of illite/smectite mixed layer (I/S), ratio of illite to I/S, and three-dimensional structure of illitic minerals, do not represent the progress of a smectite-to-illite transformation, but these characteristics clearly reflect the temperature during illitization of kaolin.

Illitization of Diagenetic Kaolinite-to-dickite Conversion Series: Late-stage Diagenesis of the Lower Permian Rotliegend Sandstone Reservoir, Offshore of the Netherlands

Daniel Beaufort

Papers

Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review

Kaolinite-to-dickite reaction in sandstone reservoirs

Application of chemical geothermometry to low-temperature trioctahedral chlorites

Chlorite and chloritization processes through mixed-layer mineral series in low-temperature geological systems – a review

Illitization of Diagenetic Kaolinite-to-dickite Conversion Series: Late-stage Diagenesis of the Lower Permian Rotliegend Sandstone Reservoir, Offshore of the Netherlands