Michel Rautureau

Characterization of overgrowth structures formed around individual clay particles during early diagenesis

The coarse (0.4–2 µm) clay fraction of an Albian black shale collected in the Atlantic Ocean (Deep Sea Drilling Project leg 11) consists chiefly (90–95%) of smectite and 5–10% illite. Both minerals are locally surrounded by overgrowth structures, such as fine laths about 0.05–0.4 µm long and 0.02–0.1 µm wide. Individual laths or assemblages of laths protrude from the center of smectite flakes at angles of about 60° to each other. Laths occur around illite crystals in a similar manner or coalesce into a rim that consists of 0.05–0.1-µm-size particles. On the basis of scanning transmission electron microscopy: (1) the center of individual illite crystals consists of a dioctahedral mineral, but the overgrowth structures are Al-Fe beidellites; and (2) the smectite flakes have highly variable compositions, but correspond chiefly to Fe-Al-beidellite, whereas the overgrowths are compositionally close to montmorillonite.The overgrowth structures seem to have formed during early diagenesis. The chemical composition of overgrowths around illite and smectite tend to be similar in response to the new environment, implying an addition of silica to both materials.RésuméLa fraction argileuse (0,4-2 μm) d’un échantillon de black shale albien de l’Atlantique (Deep Sea Drilling Project leg 11) surtout formée de smectite (90–95%) et d’illite (5–10%) a été étudiée. L’étude morphologique des particules en microscopie électronique montre qu’elles sont souvent entourées de surcroissances généralement formées de lattes très fines longues de 0,05 à 0,4 Mm et larges de 0,02 à 0,1 μm. Autour des flocons de smectite, les lattes peuvent être isolées ou former des assemblages de 4 ou 5 lattes formant fréquemment des angles de 60° entre eux. Des faciès identiques se rencontrent autour des illites mais ces minéraux peuvent aussi être entourés de lattes courtes (0,05 à 0,1 μm) et coalescentes formant une auréole plus ou moins continue autour du cristal.L’analyse de ces argiles par microscopie électronique analytique montre: (1) que la composition du centre des particules d’illite correspond à des minéraux dioctaédriques mais les lattes qui les entourent sont des beidellites Al-Fe; (2) que la composition du centre des smectites, beaucoup plus variable d’une particule à l’autre, correspond à des beidellites Fe-Al et les lattes qui les entourent à des montmorillonites.Ces sur-croissances semblent se former au cours de la diagenèse précoce. Le fait que la composition des lattes poussant autour des illites converge vers celle des lattes entourant les smectites constitue une indication de la réponse des minéraux à un changement de milieu. Du point de vue chimique, ces modifications nécessitent toute deux un apport de silice.

Analysis of zinciferous clays from central Tunisia using a scanning transmission electron microscope (STEM)

Abstract Between Late Cretaceous and Miocene time the central part of Tunisia emerged. During this period a karstic system developed in Senonian limestones of the Ain Khamouda area. It is known that three facies occur in the resulting caves: (1) red mineralised crust containing goethite, hemimorphite and smithsonite; (2) white clay containing 0.1–8.5% ZnO; (3) Miocene sand and sandstone. The white clay has been studied using STEM (scanning transmission electron microscopy) in order to determine with which minerals Zn is associated. Two zinciferous phases were found, the first being a swelling clay of sauconite type, the second a nearly amorphous Zn-hydroxide gel. Halloysite which is the main component of the white clay seems totally devoid of Zn. The difference between Zn minerals contained in the crust and in the clay can be related to pH gradients. Minute particles (3–10 nm) of pure Ag, were found in the clay, indicating that the present mineralisation is probably related to the alteration of sulphides.

Clays and Health

First book in English which describes the pharmaceutical and therapeutic benefits of clays in terms of their physical and physicochemical properties. Provides a concise history of the use of clay in human health practices. Unlike popular texts, this book describes the customary applications of clays and explains the mode of action causing the palliative effect

General Information on Clay Applications for Health and Well-Being

This chapter reports on the ordinary clay applications in the field of health: first, the function of the nature of the pathologies to be treated, second, the function of the clay potentialities to treat certain pathologies, and third, the function of the principal reactivity domains pertaining to clay and living organisms.

Historical Aspects of a Natural Pharmacopeia: Clay in the Corpus of The Medieval Pharmacopeia Written in Arabic

This chapter opens with an historical presentation of some translations of Ancient Greek medical texts. They reached us partly thanks to translations into Arabic carried out during the Middle Ages. These texts were progressively enriched and thereafter evolved autonomously. Stories of conquests and religions, both ancient and medieval, are superimposed on the evolution of this knowledge, without being the exclusive causes. Therapies based on clay and its various daily uses are described in the corpus of profane texts of pharmacy, pharmacopeia, medicine, and rules for healthy living. In this chapter these points, disclosed in chronological order and by topics, are dealt with, concentrated only on some fundamental studies in medicine and pharmacy.

Principal Modes of Clay Use

There is a long tradition of the use of clay for therapeutic purposes. The so-called healing or curative clay can be used either for internal or external applications. The so-called edible clay is a type of healing clay used for internal applications, ingested in the form of clay/potable water dispersions (argillic water), bits/pieces of natural clay, or even manufactured cookies or wafers consisting of a clay–animal fat blend and slowly chewed.

Therapies Based on Clay

The therapies based on clay dealt with in this chapter are classified in two main groups, physical therapies and chemical therapies, involving either physical or chemical exchanges between the clay- bearing material and the human body, respectively. Physical therapies involve energy exchanges that can be induced during a massage by employing mechanical pressure on the previously heated (maximum at 45–50°C) clay pack, and from the pressure and heat being applied; the beneficial effects of improvement of muscular tone and blood circulation through abrasive and gumming action may occur. Chemical therapies involve chemical exchanges that could be promoted and developed by the applied pressure and heat. Beneficial effects could result from the chemical exchanges of the transdermal absorption of eventual bioessential elements and compounds existing in the liquid phase.

Clay Reactivity Depending Upon the Crystallochemical Properties of Clay Minerals

The crystallochemical models of clay mineral structures are described in this chapter because clay properties and inherent reactivity depend entirely on the specificities of those structures. Clay reactivity is strongly conditioned by the surface properties of clay mineral particles that are basically dependent on the particle global electric charge and its spatial distribution pattern, different from basal surfaces to edge surfaces. Particle electric charge results mainly from atomic substitutions that occur in both the octahedral and tetrahedral layers. In clay minerals bearing interlayer spaces chemical reactivity also possibly occurs on internal surfaces.

Provisioning, Recycling, and Trade of Clay

Natural clay to be used in the field of health and well-being, whether used as it occurs at its natural site, or after extraction from the deposit, is submitted to a refining processing in order to concentrate the finest grain fraction (enriched in clay minerals sometimes associated with organic compounds and finely grained carbonates, potentially the most interesting components in therapeutic or cosmetic terms). In the first situation clay in the form of paste (after being mixed with mineral water, e.g., seawater) is used at its natural site or at a nearby site as mud in mud therapy treatments, or as small pieces chewed and ingested, or even ingested after being dispersed preferentially in potable water providing argillic water. Processed clay is available on the market in two main states: powders (used in pharmaceutical formulations) and paste (used in peloids to be applied, for instance, at spa resorts after undergoing more or less complex manipulation and maturation), and in both states a microbiological check-up is necessary to assure sanitary safety. This sanitary safety is also required when recycling previously used clay paste.

Clay and Clay Mineral Definition

Any science, scientific field, or scientific domain requires a well-established and defined object of study as well as appropriate methodologies to develop knowledge about that object. However, over time the definition or concept of the object of study can undergo modifications and adaptations due to scientific advances, both in theoretical and experimental terms.