Clay Minerals 

About: Clay Minerals is an academic journal published by Cambridge University Press. The journal publishes majorly in the area(s): Clay minerals & Illite. It has an ISSN identifier of 0009-8558. Over the lifetime, 2671 publications have been published receiving 77766 citations. The journal is also known as: Clay minerals.

Halloysite clay minerals — a review

Abstract: 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.

Cation Site occupancy in chlorites and illites as a function of temperature

Abstract: A B S T RA C T : The relationships between the composition and the crystallization temperature of chlorites and illites have been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories, as the main changes in physical and chemical conditions and mineralogy are related to progressively increasing temperature with depth. Temperature was estimated from combined geothermometric approaches, and especially from fluid inclusion studies on quartz coexisting with clays. The Al(lv) content in the tetrahedral site of chlorites, and the K content and total interlayer occupancy of illites increase with temperature. These chemical changes are mainly related to the marked decrease in the molar fraction of the Si(lv)-rich end-members (kaolinite for chlorites, and pyrophyllite for illites) which become negligible at ~ 300~ Other chemical changes, such as the variation in Fe and Mg contents, are partly influenced by temperature, but are strongly dependent on the geological environment, and consequently on the solution composition. The empirical relationships between chemical variables and temperature were calibrated from 150-300~ but extrapolations at lower and higher temperatures seem possible for chlorites. Such geothermometers provide tools for estimating the crystallization temperature of the clays, and are important for the study of diagenetic, hydrothermal and low-T metamorphic processes. Clay minerals are the most abundant minerals in most of the geological environments submitted to temperatures from 50 ~ to 350~ where estimation of the crystallization temperature of the clay minerals may be difficult. Most of the classical geothermometers cannot be applied, fluid inclusions may be absent, and experimental data are scarce. Nevertheless, such temperature estimations are of critical importance for geological studies related to oil field exploration, as well as for diagenetic and low-T metamorphic processes. 1"here are three types of chemical or crystallographic change occurring in the clay fraction of rocks which may indicate temperature of crystallization. (1) The changes in the clay mineral assemblages described in studies of the burial metamorphism of sediments (Weaver, 1959; Dunoyer de Segonzac, 1970; Perry & Hower, 1970; Velde, 1977) and the thermal metamorphism of rocks in geothermal fields (Schoen & White, 1966; Steiner, 1968; Tomason & Kristmannsdottir , 1972; Cathelineau & Izquierdo, 1988). However, only the boundaries between two mineral assemblages may yield a temperature estimate, largely restricting their use.

Properties and applications of palygorskite-sepiolite clays

Abstract: The palygorskite-sepiolite group of clay minerals has a wide range of industrial applications derived mainly from its sorptive, rheological and catalytic properties which are based on the fabric, surface area, porosity, crystal morphology, structure and composition of these minerals. For assessing potential industrial uses, the mineralogical and chemical composition of the clay and its basic physical and physico-chemical parameters must be determined. Then some particular properties of commercial interest can be modified and improved by appropriate thermal, mechanical and acid treatments, surface active agents, organo-mineral derivatives formation, etc. In this paper, a revision of the principal characteristics of commercial palygorskite-sepiolite clays is presented, and potential uses are suggested according to these data. New products and applications are being investigated and those concerning environmental protection in particular, are noted. Finally, possible health effects of these elongate clay minerals are discussed. While commercial deposits of palygorskite and sepiolite are rare, these two clay minerals occur relatively frequently in sediments and soils. Both palygorskite and sepiolite clays are so- called 'special clays'. The annual production in the western world for the former is estimated to be around two million tonnes; production comes mainly from the southeastern USA (Miocene deposits in Florida and Georgia), about 1.8 million tonnes in 1989 (Ampian, 1991), and from Senegal, Spain, Australia, India, Turkey, South Africa and France to a much smaller extent. Sepiolite is less abundant than palygors- kite. The former is a typically Spanish mineral; in fact, over 90% of sepiolitic clays are produced in Spain (also from Miocene deposits). Other small operations are in Nevada (USA), Turkey and China. The annual production of sepiolite in Spain is close to 800,000 tonnes (O'Driscoll,

The Oxides and Hydroxides of Iron and Their Structural Inter-Relationships

Abstract: The transformations ia-x the iron oxide-hydroxide system have been interpreted in a rational crystallochemical manner, some bring characterized as topotactic and some as non-topotacfic. Crystallographic measurements have been made on the more reactive or metastable phases, particularly on the "green rusts." The oxyhydroxides ~-]~eOOFI and ~-FeOOH have been examined more fully, but data on ald the phases have been checked. New data on transformations, such as FeCOa---> FeO and Fe(OH)~-+ FeO are reported.

Stable isotope geochemistry of clay minerals; The story of sloppy, sticky, lumpy and tough, Cairns-Smith (1971)

Abstract: The equilibrium H- and O-isotope fractionations can be approximated by the following equations which are based on experimental, empirical and/or theoretical data: Hydrogen: 1000 In ~kaolinite-water ~" -2.2 x 106 X T -2 - 7.7 Oxygen: 1000 In ~kaolinite-water = 2.76 x 106  _ 6.75 1000 In (~smectite-water = 2.55 x 106x T -2 - 4.05 1000 In ~illite-water = 2.39 X 106  T -2 - 3.76 The equilibrium H-isotope fractionation factors vs. 106  T -2 for kaolinite and probably smectite and illite are monotonic curves between 350-0~ More complex curves, with a minimum fractionation near 200~ are probably influenced by surface effects and/or disequilibrium fractionations among the different hydrogen sites. The H-isotope fractionations between smectite-water increase by 70% from Fe-poor montmorillonite to nontronite at low temperatures. The pore-interlayer water in smectite H-isotope fractionation at low temperatures is ~20__+ 10%. The presence of organic matter can modify both the ~SD value of the clay analysis and its 'water' content. Clays -- kaolinite, illite, smectite and probably halloysite -- tend to retain their D/H and 180/160 ratios unless subjected to more extreme diagenetic or metamorphic conditions or special local processes. Kinetic information is still only qualitative: for comparable grain sizes, hydrogen exchanges more rapidly than oxygen in the absence of recrystallization. Low-temperature diffusion coefficients cannot be calculated with sufficient precision from the higher temperature exchange data. The H- and O-isotope studies of clays can provide useful information about their conditions of formation.