Clay and glauconite fractions separated from sedimentary rocks in Israel were analysed for their mineralogical composition by X-ray diffraction and dated by the K-Ar method. The main goal was to evaluate early diagenetic processes which might have affected the K-Ar system. One series of samples was taken from two contemporaneous mid-Albian to mid-Turonian (~105–91 Ma) shallow marine successions in which early diagenetic K-feldspar was found to be widespread. Another series was of samples of large spatial distribution associated with a mid- Turonian emergence event. None of the outcrops had been subjected to high temperatures due to deep burial or other thermal events. The abundant clay minerals in the first series are randomly ordered illite-smectite (I-S) phases of various discrete and mixed compositions. Illite, kaolinite, ordered I-S and palygorskite are sometimes present. The variability in clay assemblages and I-S composition within short vertical distances and the proximity to the provenance implies mostly a detrital origin for the clay minerals. The K-Ar ages of clay fractions in the first series are no older than 30% of the stratigraphie ages, much younger than the known detritus provenance ages. A few have known stratigraphie ages and one is younger by 10%. The K-Ar ages of associated glauconite fractions are younger by 5–13% than the stratigraphie ages. The ages of the clay fractions of the second series, which are on average more illitic, are mostly younger and no older than 22% more than the stratigraphie age. The age distribution and the clay mineralogy in the two series suggests that illitization of detrital I-S phases may start right after deposition under specific conditions, namely, contact of the sediments with K-rich brines, produced by evaporation in restricted marine environments. The process may continue from a few to many millions of years after burial, as long as K-enriched solutions are available. However, in most cases the near-surface temperatures did not enable a completion of the K-Ar reset process. It seems that low-temperature illitization is better explained as being dependent on solution composition and not on wetting-drying cycles.

Diagenesis in the Podhale and Orava Paleogene flysch basins and in the underlying Mesozoic structural units was studied by XRD measurement of the percent smectite in the mixedlayer illite-smectite from shales and K-Ar dating of the illite-smectite from bentonites, supported by XRD quantitative mineral analysis, grain density, and porosity measurements of the bulk shales. The diagenetic mineral reactions identified in the flysch shales include illitization of smectite (>60 to <5%S), dissolution of K-feldspar and kaolinite, crystallization of quartz, albite and chlorite. An unusually large amount of basin history information was obtained by combining the illite-smectite data from wells and from the present erosional surface of the basin.

The rocks underwent burial diagenesis at a stable geothermal gradient similar to the present-day value of 21±2°C/km. The maximum burial temperatures were reached very quickly (high sedimentation rate) close to the basin inversion time, at ∼17 Ma in the western part and 18 Ma in the eastern part.

The basin floor, which included the present-day Tatra Mts., was inclined towards the East. The thickness of the sedimentary filling of the basin ranged from 3.5–4.5 km in the western Tatra (removed entirely), to 5–6 km in the western Podhale (<3–4 km removed), to 6.5–7.5 km in the eastern Podhale (>4–5 km removed), and even more in the eastern Tatra and Spisská Magura close to the Ružbachy Fault. These data imply a major subsidence followed by uplift of the Podhale plus Tatra block along the Ružbachy Fault and the deposition of a thick sequence of Lower Miocene sediments over the entire area (latter removed by erosion).

The Mesozoic rocks of all the structural units underlying the flysch basin underwent advanced diagenesis (maximum palaeotemperatures of 160–270°C) during an Upper Cretaceous tectonic burial event at ∼80–90 Ma. The tectonic overload was removed before the Eocene transgression (49–42 Ma).

The regional distribution, mineralogy, petrology and chemistry of the detrital and authigenic clay minerals associated with the Permo-Triassic strata (excluding the Rotliegend: see Ziegler, 2006; this volume), of the onshore and offshore regions of the British Isles are reviewed within their stratigraphical framework. The origin of these clay minerals is discussed in relation to current hypotheses on the developments of the Mg-rich clay mineral assemblages associated with the evaporitic red-bed Germanic facies of Europe and North Africa.

Composite clay mineral successions are described for seven regions of the British Isles — the Western Approaches Trough; SW England; South Midlands; Central Midlands; the Cheshire Basin; NE Yorkshire; and the Central North Sea. The detrital clay mineral assemblages of the Early Permian strata are variable, consisting of mica, smectite, smectite-mica, kaolin and chlorite, whereas those of the Late Permian and the Trias are dominated by mica, usually in association with minor Fe-rich chlorite. The detrital mica consists of a mixture of penecontemporaneous ferric mica, probably of pedogenic origin, and recycled Pre-Permian mica. In the youngest Triassic strata (Rhaetian), the detrital clay assemblages may contain appreciable amounts of poorly defined collapsible minerals (irregular mixed-layer smectite-mica-vermiculite) and kaolin, giving them a Jurassic aspect. There are two types of authigenic clay mineral assemblages. Kaolin may occur as a late-stage diagenetic mineral where the original Permo-Triassic porewaters of the sediment have been replaced by meteoritic waters. A suite of early-stage diagenetic clay minerals, many of them Mg-rich, are linked to the evaporitic red-bed facies — these include sepiolite, palygorskite, smectite, irregular mixed- layer smectite-mica and smectite-chlorite, corrensite, chlorite and glauconite (sensu lato). The sandstones and mudstones of the onshore regions of the British Isles display little or no difference in their detrital and authigenic clay mineral assemblages. In contrast, the sandstones of the offshore regions (North Sea) show major differences with the presence of extensive chloritic cements containing Mg-rich and Al-rich chlorite, irregular mixed-layer serpentine-chlorite, and mica.

In this study, the influence of pH, electrolyte concentration and type of ionic species (such as LiCl, NaCl, KCl, RbCl, CsCl, CaCl2, AlCl3) on the electrokinetic properties (zeta potential and electrokinetic charge density) of montmorillonite has been quantified. The zeta potential of montmorillonite particles did not change significantly with change in pH. The valencies of the ions have proven to have a great influence on the electrokinetic behaviour of the suspension. There is a gradual decrease in the zeta potential (from —24 mV to —12 mV) with increase in monovalent electrolyte concentration (from 10-4 M to 10-1 M). At any monovalent electrolyte concentration, the magnitude of the zeta potential increased with the electrolytes in the order Li+ > Na+ > K+ > Rb+ > Cs+. The zeta potential of the montmorillonite minerals in CaCl2 solutions illustrated the same behaviour as the monovalent cations. Less negative values were obtained for the CaCl2 electrolyte (∼–10 mV) due to the greater valence of the ions. A sign reversal was observed at an AlCl3 concentration of 5 x 10-4 M, and, at greater concentrations, zeta potential values had a positive sign (∼20 mV).

The electrokinetic charge density of montmorillonite showed similar trends of variation in mono and divalent electrolyte solutions. Up to concentrations of ∼10-3 M, it remained practically constant at ∼0.5 x 10-3Cm-2, while for greater electrolyte concentrations the negative charge produced more negative values (–16 x 10-3Cm-2). The electrokinetic charge density of montmorillonite particles was constant at low AlCl3 concentrations, but at certain concentrations it increased rapidly and changed sign to positive.

MX-80 is a bentonite clay from the Clay Spur bed, Wyoming, USA, consisting of ~80 wt.% Na-rich montmorillonite and is a leading candidate material for use in engineered barriers within underground nuclear waste disposal sites in Switzerland and Sweden. The diffusive invasion of groundwater into the engineered barriers is likely to cause the dry high-density bentonite to swell and evolve into a less-dense, water-rich gel during re-submergence of the shafts and galleries. Data on H20 diffusivity within water-rich bentonite gels are therefore essential to the safe design of the engineered barriers. To address this need, the self-diffusion coefficient, D, of 1H2O molecules in water-rich MX-80 bentonite gels was measured using the pulsed-gradient spin-echo method of 1H nuclear magnetic resonance spectroscopy at 0.47 T; D was measured over a wide range of temperatures (20.6–70.1°C) and of bentonite volume fractions (0 to 17.2 vol.%). The results showed that D increased markedly to values of bulk water self-diffusivity as the bentonite volume fraction decreased towards 0 vol.%. The activation energy of the diffusion process for the gels was approximately equal to that for bulk water. As a result, the normalized H20 self-diffusivity, D/D0, was approximately independent of temperature, where D0 is D in bulk water. The D/D0 data for ≤6.39 vol.% bentonite fraction were successfully fitted to a porous clay gel model that involves unbound water molecules that diffuse in the pore space by avoiding randomly placed discoidal obstacles (clay particles) of a high aspect ratio. The D/D0 data for MX-80 were similar to data for SWy-2 (Wyoming bentonite from the Newcastle formation) and Kunigel-Vl (bentonite from Yamagata, Japan), suggesting that all three bentonites are equally suitable candidate materials, in terms of water diffusivity performance, for use within engineered barriers.

Brindley et al. (1951) reported the earliest efforts to obtain international collaboration on nomenclature and classification of clay minerals, initiated at the International Soil Congress in Amsterdam in 1950. Since then, national clay groups were formed, and they proposed various changes in nomenclature at group meetings of the International Clay Conferences. Most of the national clay groups have representation on the Nomenclature Committee of the Association Internationale pour l'Etude des Argiles (AIPEA, International Association for the Study of Clays), which was established in 1966. The precursor committee to the AIPEA Nomenclature Committee was the Nomenclature Subcommittee of the Comité International pour l'Etude des Argiles (OPEA, International Committee for the Study of Clays).

Raw clay materials manufactured for stoneware use are typically compounds of kaolins, silicas and feldspars. Two stoneware clay materials examined here were chosen because each is representative of the range of manufactured clay bodies. Samples were fired in an oxidizing atmosphere to a range of temperatures between ∼1000 and 1300°C. Sample dimensions, density, porosity and mechanical properties under compression were measured as a function of firing temperature. Thin sections, showing particles and their relationship to pore/void structures, were prepared, recorded under scanning electron microscopy (SEM), and analysed. The observed changes in microstructure can be related to previously described metamorphic and micro-eutectic reactions and a gradual sintering process. Indications of changes to apparent porosity are further amplified by measured changes of mechanical properties. The modulus of elasticity increases with reduction in porosity to a point at which porosity ceases to be the principal determining factor. The critical Griffith's crack length, calculated from fracture-strength measurement, exhibits a similar trend. The onset of these changes coincides with a significant increase in sealed porosity and with the microstructural metamorphosis as revealed by SEM.

The nature, distribution and origin of clay minerals in the hydrocarbon-bearing Permian Rotliegend sandstones of the North Sea and the adjacent areas of the Netherlands and Germany are reviewed. The clay minerals occur as detrital coatings of smectite and smectite-illite on the surfaces of sandgrains, and as later diagenetic cements of kaolinite, chlorite (two varieties), and illite in the pore spaces of those sandstones. Two diagenetic clay mineral assemblages are predominant in the Rotliegend of the North Sea. The kaolinite-illite assemblage is restricted to the Rotliegend of shelf areas which underwent shallow burial followed by strong Jurassic/Cretaceous (Late Cimmerian) structural inversions, whereas the illite-chlorite assemblage is associated with basinal areas that underwent deep and rapid burial throughout the Mesozoic.

The factors controlling mineralogy, crystal chemistry and morphology of those diagenetic clay minerals, as well as their regional distribution and origin, are numerous, complicated, and inter- related. Evidence suggests that the following aspects were important parameters: (1) variations in the original depositional arid desert environment; (2) the chemistry and flow patterns of the porewaters; (3) temperature and timing of clay mineral formation; (4) local burial history; (5) the presence or absence of meteoric water; and (6) the structural setting of the Rotliegend sandstones.

Oxygen isotope data indicate that the illite cements formed over a wide range of temperatures (24–140°C) that is consistent with the deep burial conditions prevailing in the palaeo-basins. In contrast, oxygen isotopes indicate that kaolinite cements formed over a more restricted temperature range (40–80°C) and under the influence of meteoric water penetrating the sandstones of the shelf areas as a result of their Late Cimmerian uplift and associated erosion. Hypotheses suggesting that the absence of kaolinite cement from the deeply buried Rotliegend sandstones is caused by its illitization during burial, and that the chlorite cements have formed by the alteration of earlier smectite, smectite-chlorite and corrensite cements, are not supported by evidence.

The Carboniferous in Britain is diverse and this is reflected in the clay mineral assemblages. Several factors affecting the assemblages are identified including climate, rates of weathering and erosion, source rocks in the hinterland, preservation of palaeosols, whether the source rocks are nearby or distant, sorting during transportation, the presence of altered volcanic ash-falls in the depositional environment and the extent of burial diagenesis. There are temporal and geographic variations in the clay mineral assemblages in the mudrocks as a result of these controls. There are also clay-rich rocks that differ from the normal mudrocks and a knowledge of the clay mineralogy of these is a necessary prerequisite to a full understanding of their origins. Mudrocks falling in this category, and described below, include bauxitic clays, flint clays, fragmental clay rocks, tonsteins and K-bentonites and various palaeosols.

K-Ar dating of mixed-layer illite-smectite from clay fractions extracted from pyroclastic horizons was used to address the controversy about the age and mechanism of the thermal alteration of Carboniferous rocks from the Upper Silesia Coal Basin (USCB). The clay fractions were also investigated by X-ray diffraction in order to select for dating samples possibly rich in illitesmectite, and to evaluate the K-Ar dates for possible contamination by K-bearing pre-diagenetic minerals, of pyroclastic or epiclastic origin.

The K-Ar dates document intense Variscian tectonic burial illitization produced by thrusting (~290 Ma) in the SW of the basin, and the lack of intense burial illitization in the NE, which is consistent with sedimentological models of the basin. The burial illitization in its final phase (<30%S in illite-smectite) involved incorporation of measurable amounts of ammonium cation in the illite structure (substitution for K).

Advanced illitization in the NE of the basin is much younger than its tectonic inversion (uplift and erosion started in Permian), and the corresponding K-Ar dates have to be interpreted as the result of a Mesozoic thermal event, which produced widespread pervasive illitization at shallow depth. This event was dated at 175 Ma, but it may have started earlier and could have lasted longer. This conclusion is consistent with widespread evidence of a major Mesozoic thermal event all over Central Europe, produced by rifting and lithospheric thinning during the opening of the Tethys and Atlantic oceans.

This study demonstrates that smectite illitization histories may be very complex, and that the nature of the illitization mechanism results in mixed K-Ar dates encompassing pro-longed or multiple illitization histories. Dating of several grain-size fractions may help to unravel such histories.

When a calibration using data from Neogene sedimentary basins is applied, vitrinite reflectance and %S in I-S indicate similar palaeotemperatures of tectonic burial diagenesis in the USCB, but they produce very different estimates of the temperature of the thermal event.

The distribution and origin of clay minerals in Carboniferous sandstone reservoir rocks, onshore and offshore UK, is reviewed using both published and unpublished sources. The clay mineralogy for many of the Carboniferous reservoir sands tends to be similar, with the detrital clays predominantly illitic whereas the diagenetic clay assemblages are dominated by kaolin with usually lesser amounts of illite. The main exception to this pattern is found in the Dinantian sandstones of the Clair Basin where significant amounts of smectite are present. Three stages of diagenetic kaolin formation are widely recognized. Firstly eogenetic and/or telogenetic kaolinite; secondly mesogenetic kaolin; and thirdly the partial or complete transformation of kaolinite to dickite during deep burial. In addition to the formation of diagenetic clay phases, the sandstone reservoirs also display a complex diagenetic history involving cementation and dissolution processes. These have affected the reservoir properties of the sandstones but the depositional facies architecture still exerts a major recognizable influence on reservoir porosity-permeability characteristics. The abundance of kaolin cements shows no clear correlation with variations in porosity and permeability for Carboniferous reservoirs. Pore- filling smectite affects reservoir porosity and permeability in the Dinantian of the Clair Field, and could be a potential source of serious reservoir damage arising from swelling.

The Devonian sedimentary rocks of the UK are made up of a continental red bed facies, the Old Red Sandstone (ORS), and sediments of a marine origin. The latter are confined to southwest England whereas the ORS occurs much more extensively, particularly in South Wales, the West Midlands, Northern England, the Midland Valley of Scotland and the Orcadian basin. The ORS also occurs extensively offshore where it contains important hydrocarbon reservoirs. Highly variable suites of clay mineral assemblages are characteristic of the ORS. In the West Midlands and Monmouthshire, the Downton Group is characterized by illitic, smectitic, and mixed-layer illite-smectite minerals. A tuff bed (Townsend Tuff) also contains expansible minerals but when the bed is traced westwards it is found that the clay mineralogy changes progressively to an illite-chlorite assemblage, suggesting the influence of diagenetic or metamorphic change. It is not known, however, whether such a transformation is typical of the Downton Group as a whole. The overlying Ditton Group in its eastern outcrops contains a high-spacing mineral identified as tosudite, together with regularly interstratified illite-smectite and well crystallized kaolinite. Further west this assemblage gives way to illite and chlorite, with the latter being trioctahedral or dioctahedral, while in Dyfed the Ditton Group may contain smectite and poorly crystallized kaolinite in addition to illite and chlorite. The geographical distribution of clay minerals in the Ditton Group may also be accounted for by progressive diagenetic to low-grade metamorphic reactions, although it is necessary to postulate retrogressive diagenesis to account for the smectite and kaolinite that occur in the Dyfed samples. The clay mineralogy of the overlying Brecon Group and the Upper ORS also consists of mixtures of illite and chlorite in the west and central parts of the region. No data are available for the Brecon Group in the eastern parts of the outcrop but the Upper ORS from around Monmouth and Portishead contains assemblages rich in kaolinite and mixed-layer illite-smectite with only minor amounts of chlorite. The distribution of clay minerals in the Upper ORS is again suggestive of a progressive westerly increase in the influence of diagenetic alteration, although the influence of provenance cannot be discounted.

In Scotland the clay mineralogy of the Lower ORS in the Midland valley is characterized by a variety of interstratified minerals, including regularly interstratified trioctahedral chlorite-vermiculite, a tosudite mineral similar to that described from South Wales and illite-smectite, as well as occasional illite, chlorite and smectite. The oldest Stonehaven Group is kaolinitic but in the younger groups kaolinite is either completely absent or present in only minor amounts. It is clear that detrital inputs, particularly from associated volcanic rocks, have contributed to the clay minerals found in these rocks, although the contribution could be indirect with diagenetic clay minerals forming from volcanic detritus after deposition. Diagenetic alteration may also be important, particularly with respect to the origin of the tosudite mineral. The Middle ORS lacustrine sediments of the Orcadian Basin of Scotland are characterized by mixtures of trioctahedral chlorite and dioctahedral illite, with interstratified chlorite-smectite, illite-smectite, kaolinite and occasional reports of minor montmorillonite. The most recent interpretations of the origins of the clay minerals in these rocks emphasize the role of progressive diagenetic and low-grade metamorphic reactions, based on correlations of clay mineral assemblages and parameters such as illite crystallinity with organic maturation data. This interpretation argues that the illite-smectite in the shales is derived largely from a precursor detrital smectite. However, the finding of two populations of morphologically and structurally distinct illite-smectite particles in the Middle and Upper ORS sandstones suggests a more complex picture involving different diagenetic episodes. In addition, the likelihood of a smectitic-rich detrital input to the ORS may also be a point of debate. The clay mineralogy of the North Sea offshore is also described briefly, in addition to the marine Devonian in southwest England. The latter is characterized by chlorite and illite assemblages of low-grade metamorphic origin, although smectite and kaolinite are also found occasionally in these rocks. The offshore ORS, however, contains a variety of clay minerals, including an assemblage similar to that found in the Lower ORS south of the Highland Boundary Fault and notably contains a tosudite-like mineral.

Lower Palaeozoic rocks crop out extensively in Wales, the Lake District of northern England and the Southern Uplands of Scotland; they also form the subcrop concealed beneath the English Midlands and East Anglia. These mainly marine sedimentary rocks were deposited in basins created during plate tectonic assembly of the various terranes that amalgamated to form the British Isles, 400-600 Ma ago. Final amalgamation occurred during the late Lower Devonian Acadian Orogeny when the basins were uplifted and deformed, producing belts of cleaved, low-grade metasediments, so-called slate belts, with a predominantly Caledonian (NE-SW) trend. The clay mineralogy of mudrock lithologies - including mudstone, shale and slate - found in these belts is reviewed. Using X-ray diffraction data from the <2 μm fractions of ~4500 mudrocks samples, clay mineral assemblages are summarized and discussed in terms of diagenetic and low-grade metamorphic reactions, and the metapelitic grade indicated by the Kübler index of illite crystallinity.

Two sequences of clay mineral assemblages, or regional assemblages, are recognized. Regional Assemblage A is characterized by a greater diversity of clay minerals in assemblages from all metapelitic grades. It includes K-rich, intermediate Na/K and Na-rich white micas, chlorite and minor amounts of pyrophyllite. Corrensite, rectorite and pyrophyllite are found in the clay assemblages of contact or hydrothermally altered mudstones. K-white micas are aluminous and phengite-poor, with b cell dimensions in the range 8.98-9.02 Å. Regional Assemblage B has fewer clay minerals in assemblages from a range of metapelitic grades. Phengite-rich K-mica is characteristic whereas Na- micas are rare, and absent in most assemblages; chlorite is present and minor corrensite occurs in mudrocks with mafic-rich detritus. Minor amounts of kaolinite are sporadically present, but dickite and nacrite are rare; pyrophyllite and rectorite are generally absent. The b cell dimensions of K-white mica in Regional Assemblage B are in the range 9.02-9.06 Å. The two regional assemblages are found in contrasting geotectonic settings. Regional Assemblage A is characteristic of the extensional basin settings of Wales, the northern Lake District and the Isle of Man. These basins have a history of early burial metamorphism associated with extension, and syn-burial or post-burial intrusive and extrusive volcanic activity. Intermediate Na/K mica probably developed from hydrothermal fluids generated around submarine volcanic centres. Deep diagenetic and low anchizonal clay mineral in these basins may develop a bedding-parallel microfabric. Chlorite-mica stacks also occur in the extensional basins and the stacking planes represent another type of bedding-parallel microfabric. Both types of microfabric are non-tectonic and developed by burial during the extensional phase of basin evolution. Regional Assemblage B is developed in the plate-convergent settings of the Southern Uplands and the southern Lake District. In the accretionary complex of the Southern Uplands the processes of burial diagenesis, metamorphism and tectonism were synchronous events. In both plate- convergent basins, low temperatures and tectonic fabric-formation had an important role in clay mineral reactions, whereas hydrothermal fluids played no part in clay genesis.