Petrographic study of the Frewens sandstone, Upper Cretaceous Frontier Formation, documents reservoir-scale diagenetic heterogeneity. Iron-bearing calcite cement occurs as large concretions that generally follow bedding and are most common near the top of the sandstone. Median thickness of the concretions is 0.6 m, length 4.5 m, and width 5.7 m; median volume is 5.2 m3. Concretions comprise 12% of the sandstone.

The minus-cement porosity of concretion samples is low, indicating that the calcite precipitated near maximum burial depth. Isotopic and burial history data suggest that the calcite precipitated at ~54°C from evolved meteoric water enriched in 18O or from a mixed meteoric±marine pore-water. Shell-bearing transgressive shales above the Frewens sandstone are interpreted to be the source of calcium carbonate. Concretions of this size and distribution would influence fluid flow in a reservoir and would reduce the amount of hydrocarbons in place.

The increase in specific surface of kaolinite (K) and pyrophyllite (P) induced by dry grinding in an oscillatory mill, proceeded during storage in water vapour. The average particle thickness, δ, changed from 42 nm (K) and 66 nm (P) in the original materials to 12 nm (K) and 20 nm (P) after water sorption (20 days at relative humidity RH = 1.0, at room temperature and pressure) and to similar values of 13 nm (K) and 16 nm (P) after grinding for 10 min (in agreement with some published data). The action of water molecules on ground clays (at the conditions indicated) resulted in a further decrease in δ. In pyrophyllite, prolonged grinding (30 min) and prolonged action of water molecules (36 days) caused a particle collapse. After pre-storing at RH = 0.5 the successive decrease in δ at RH = 1.0 was smaller.

Lors de l'étude des produits d'adsorption du benzène sur une montmorillonite cuivrique partiellement déshydratée (P4O10 et vide), la polymérisation du benzène en polyparaphénylène a été mise en évidence. Cette polymérisation a lieu au cours de cycles de déshydratation — adsorption — réhydratation à l'air, à partir de la forme rouge du complexe montmorillonite — cuivre II — benzène. Le polymère, caractérisé par spectroscopie infra-rouge, est formé dans l'espace interfoliaire de la montmorillonite comme le montrent les diagrammes de rayons X. Les mécanismes réactionnels possibles sont discutés.

Hydrating high-alumina cement will react with calcium carbonate to form the complex mineral calcium carboaluminate hydrate, 3CaO.Al2O3.CaCO3.12H2O. This mineral is reported to be capable of providing strength in concrete and so may provide an alternative to the minerals normally found in the hydration of high-alumina cement, which may under certain conditions convert to other minerals with a loss in strength. Some doubt has been cast on the stability of calcium carboaluminate hydrate and it has been found that in hydrated high-alumina cement, calcium carboaluminate hydrate decomposes at temperatures in excess of 60°C. Cube compressive strength tests on high-alumina cement and high-alumina cement-calcium carbonate pastes have shown that the latter have a lower strength than pastes made with high-alumina cement alone. When cured at 50°C the high-alumina cement-calcium carbonate pastes show a loss in strength with curing time. Cements made with the high-alumina cement-calcium carbonate mixture always have a lower strength than those made with high-alumina cement alone and so no advantage is gained from their use.

A procedure is described for the quantitative estimation of hematite, goethite and lepidocrocite in soil clays by differential X-ray diffraction combined with profile refinement. The method has been applied to clays from 12 palaeosol horizons from south-east England. Samples containing as little as 1% dithionite-extractable iron can be analysed in this way. The hematite: goethite ratio is determined to within ±3% for soil clays having ∼2.5% of each oxide and to within 10% in less favourable cases. The concentration of oxides in the soil determined solely from X-ray diffraction and from a combined chemical analysis/X-ray method are in good agreement. In addition to improving the accuracy and extending the range of iron-oxide concentrations over which analysis can be carried out, the method may, in principle, be used to provide information about the cell parameters and line profiles of each component present.

This paper describes a study of the hydraulic reactions between metakaolin (MK) and air lime using electrochemical impedance spectroscopy (EIS) and nuclear magnetic resonance spectroscopy (NMR). Tests were carried out at 20, 25 and 30°C on lime-MK pastes with 10:1 w/w ratio. Tests over 28 days allowed identification of relevant changes in the EIS signals and characterization of pastes using thermal analysis (TGA/DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and uni-axial compressive tests. Tests over shorter periods of time (up to 42 h) allowed more detailed studies of the hydraulic phases formed at the very beginning of the reactions.

Results of thermal analyses demonstrate formation of hydraulic compounds such as CSH, C4AH13 and C3ASH6 and show their evolution over time. MIP analysis demonstrates changes in pore size distribution related to the formation and trasformation of hydraulic phases. Variations of impedance response with time are shown to be associated with reaction kinetics. Changes in the NMR signal within the first 42 h of reaction are shown to be associated with the dissolution of calcium hydroxide in the pore solution. Overall, this paper demonstrates the importance of NMR in the study of hydraulic reactions in lime based materials and the ability of EIS to detect the formation of hydraulic compounds and the end of the calcium hydroxide dissolution process.

Interlayer K in eleven trioctahedral micas, with compositions ranging from fluorphlogopite to biotite, was replaced by treating cut flakes with aqueous solutions of Na salts at controlled pH values. Replacement in natural micas was faster at pH 4·5 than at pH 9, and there is a co-operative action or synergy of H+ and Na+ in replacing K+. The synergetic effect of H+ tends to be greatest in micas that lose most net negative charge when K is replaced, and increases when Fe2+ in biotite is oxidized by heating. Possible relationships between the synergetic effect and the chemical composition of micas are discussed in relation to the structure and chemical changes in the aluminosilicate layers when K is exchanged, and it is concluded that incorporation of protons into the structure is responsible for the synergetic effect.

This paper addresses the mineralogy, geochemistry, and genesis of palygorskite and associated calcretes in the Kırşehir region. In this area, the Quaternary calcretes are present within and/or on lacustrine mudstones of the Kızılırmak Formation (Late Miocene-Pliocene). The calcretes occur in the form of nodules, tubes, fracture-infills, and hard laminated crusts (hardpans). Calcrete samples are predominantly composed of calcite associated with smectite, quartz, feldspar, and minor palygorskite. The lacustrine mudstone samples consist mainly of smectite and palygorskite with minor calcite, quartz, feldspar, illite, kaolinite and amorphous material. Petrographic studies revealed that the calcrete samples are predominantly micrites that were partially converted to microsparites by recrystallization. Scanning and transmission electron microscopy images indicate that palygorskite fibres formed authigenically on and between calcite rhombs in the calcrete samples and at the edges of smectite flakes of host rocks adjacent to the calcretes. The oxygen and hydrogen stable isotope values of the calcite suggest that it precipitated from meteoric water under arid or seasonally arid climatic conditions. Calcite precipitation occurred in the vadose zone, as evidenced by desiccation cracks and vadose pisolites. The enrichment of Rb+Ba±Sr and Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE)with a distinct negative Eu anomaly are responses to the fractionation of volcanogenic feldspar and hornblende under the influence of meteoric water. The palygorskite associated with calcretes was precipitated from alkaline water rich in Si, Al and Fe and low in Mg. The palygorskite precipitation occurred at increased temperatures, characterising the advanced stage of calcrete formation which lowers the Ca content in the soil water. The required chemical elements for palygorskite and calcite were most likely derived from the dissolution of smectitic clays, ignimbrites and carbonate minerals.

Mn-substituted iron oxides were synthesized at pH 4, 6, 8, and 10 from Fe-Mn systems with Mn mole fractions (Mn/(Mn + Fe)) of 0, 0·2, 0·4, 0·6, 0·8, and 1·0, and kept at 50°C for 40 days. The Mn mole fraction in goethite was <0·07 at pH 4 but increased to ∼0.47 at pH 6. Goethite and/or hematite formed in Fe and Fe + Mn syntheses at pH 4 and pH 6 at Mn mole fractions ≤0·8, and at Mn mole fractions ≤0·2 at pH 8 and pH 10. Hausmannite and jacobsite formed at pH 8 and pH 10 at Mn mole fractions ≥0·4. In the pure Mn syntheses, manganite (γ-MnOOH) formed at pH 4 and pH 6, whereas hausmannite (Mn3O4) formed at pH 8 and pH 10. As the Mn substitution increased, the unit-cell dimensions of goethite shifted toward those of groutite, and the mean crystallite dimensions of goethite decreased.

A mixed-layer clay mineral from a Permian sandstone at Maitland, New South Wales has been identified as 2:1 mica-montmorillonite structure with ‘imperfectly regular’ interstratification. The results from Fourier transform analysis and Fourier synthesis of 00l X-ray diffraction data have not fully elucidated the interlayering patterns but have indicated that there is complete alteration in the stacking and that the 1:1 (allevardite type) layer sequence relationship is strongly developed.

X-ray diffraction, differential thermal, thermogravimetric, chemical, cation exchange and electron microscopic data for the mineral are given. The chemical analysis for the Na+-saturated material gives the structural formula

K0.90 Ca0.06 Na0.49 [Al3.52, Fe0.183+ Mg0.27 Ti0.03 (Al1.24 Si6.76) O20 (OH)4] H2O

It is considered that most of the fixed K+ and Ca++ ions are probably held in the mica interlayers, while the exchangeable components are largely accommodated in the expanded montmorillonite zones.

Two chlorites, sheridanite and clinochlore, have been examined to determine their surface charge characteristics. In order to increase their surface area and to produce a measurable surface charge, the chlorites were treated with 10−3m, 10−2m, and 10−1m HCl in 10−2m MgCl2 solutions. These treatments are shown not to alter the crystallinity of the chlorites and to produce a small pH-dependent negative charge which is not directly related to the total surface area. The clinochlore, (Si6.13Al1.84)(Al1.53FeIII0.53FeII0.18Mg9.52)O20(OH)16, is more readily attacked by the acids than the sheridanite, (Si5.43Al2.55)(Al2.90FeII0.05Mg8.86)O20(OH)16, and also produces material with greater surface area and pH-dependent, negative, surface charge. It is concluded that: (i) isomorphous substitutions in the lattice are not reflected in a permanent surface charge; (ii) the observed surface charge arises not only at the edges of the particles but also at points where the chlorite is predisposed to attack by acids; (iii) in the chlorite-acid system used, anions—probably mainly silicate—block positively charged sites.

Petrological studies of the Sherwood Sandstone of the Marchwood Borehole show that the formation is made up of two units of differing primary lithological character: a lower unit with lithic sandstone and conglomerate, and an upper unit with arkosic sandstone. A combination of compaction and calcite cementation (early and late) has severely reduced porosity and permeability in the lower unit. In the upper unit compaction is again important, but several beds have largely escaped cementation, and their primary porosity has been enhanced by leaching of feldspars. The secondary porosity reaches 7% in some samples. Oxygen and carbon isotope data for the early (calcrete) cements indicate isotopic equilibrium with typical freshwater compositions. The later cements yield more variable values, indicating precipitation under a wider range of conditions.

Physical alteration of magnetite-bearing antigorite grains is investigated in this study using Mössbauer, visible/near-infrared (VNIR) and mid-IR spectroscopy coupled with scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analyses. An expected decrease in grain size with grinding is observed using SEM. The HRTEM images illustrate that the nanophase-sized grains which adhere to larger grains have 7 Å antigorite patterns. Mössbauer spectroscopy shows the presence of antigorite, magnetite and an amorphous phase. Visible/near infrared spectra exhibit features common in serpentine. These spectra also show an increasing continuum slope with grinding, an effect which is characteristic of thin coatings or tiny grains on surfaces. Mid-IR spectra indicate the formation of fine-grained Si-OH and carbonate in these samples with grinding.

Imogolite has been identified in small amounts in clays from a soil profile developed on pyroclastics of tephrite-bassanite composition. The major part of the fine clay was an allophanic material termed proto-imogolite, characterized by an infrared spectrum with some of the features given by imogolite, including a well-developed band at 346 cm−1. Similar products have been obtained in the laboratory.

Kaolin is found in deposits of economic concentration in the Jabal Al-Harad/ Batn El-Ghoul area in southern Jordan. Ten representative kaolin samples were collected from the area and investigated for their mineralogical and chemical composition. Mineral characterization was carried using X-ray powder diffraction (XRD), thermogravimetrical analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). X-ray fluorescence (XRF) studies were conducted to determine the chemical composition of the kaolin deposits. Kaolinite was the predominant mineral, followed by quartz, with traces of illite-muscovite, Fe-bearing minerals (hematite), anatase and feldspar. The average chemical composition of the kaolin samples was 58.02 wt.% SiO2, 28.00% Al2O3, 1.48% Fe2O3, 1.26% TiO2 and 0.41% K2O (ignited basis). Dehydroxylation and mullitization temperatures (from DTA) were close to the theoretical values. Hexagonal booklets and stacks of kaolinite, as well as individual platelets, were present in the Jabal Al-Harad kaolin. Based on granulometric and descriptive mineralogical analyses, the mineral assemblages and kaolinite morphology, the Jabal Al-Harad kaolin deposit is thought to have originated from greatly weathered surfaces related to the Precambrian basement rocks. The kaolin was found to be suitable for manufacturing of common bricks, medium-fired bricks and sanitary ware, although a beneficiation process would be required; it could also be used in the refractory, white cement, paper and advanced ceramic industries.

Changes caused by pressures between 0 and 20 K bar on two samples of kaolinite have been studied. Increased pressure causes the samples to lose crystallinity, shown by a decrease in the Hinckley, Lietard and reference intensity ratio indices, as well as by the crystallite size measured from the 001 reflection. Results from DTA and solid state NMR show slight or no differences between the compressed and natural samples. Nonetheless, thermogravimetry reveals that the pressure treatment lowers the temperature at which dehydroxylation begins, but, unlike the grinding process, pressure does not alter the OH content of the samples. As a result of the increase in pressure, the IR spectra of the samples show a gradual increase in the intensity of the band at 1104 cm -1 with respect to 1112 cm -1. An increase in intensity can also be observed in the band at 936 cm ~ with respect to the band at 912 cm -1. Examination by electron microscopy reveals the existence of a large number of defects such as fractures, bends and deformations of the sheets, etc.; these are responsible for the decrease in crystallinity.

Authigenic clay mineral formation in fluvial sandstones and one brackish sandstone from the lower and middle Coal Measures of the East Midlands has been studied using XRD, optical microscopy and a variety of electron optical techniques. The sandstones are quartz-rich with minor feldspar and mica. The clay minerals present are kaolinite, chlorite and illite; they form 10–15% by volume of most of the sandstones. Both detrital and authigenic illite and chlorite are present but the kaolinite is entirely authigenic. Kaolinite and illite authi-genesis has been important in all the sandstones but authigenic chlorite is only abundant in the phyllosilicate-rich Silkstone sandstone. The controlling factors in the diagenesis of the sandstones were primary composition, environment of deposition, bed thickness, pore-fluid migration and composition, pressure and temperature. These interacting factors have been of varying importance in time and space in the diagenesis of the sandstones. Authigenic clay morphology appears to have been controlled by time and environment of formation, pore-fluid chemistry and, possibly, parent minerals.

An experimental procedure has been devised for studying the weathering of rocks under conditions approximating to those of the humid tropics. Basalt and trachyandesite gave results which were broadly similar in that a deeply weathered skin was formed on the rock particles in the atmospheric zone while a greyish skin was formed on the particles in the zone of water-table fluctuation. Granite, on the other hand, had a markedly different reaction and the particles in the atmospheric zone had a characteristic ‘pumice stone’ appearance. The new minerals formed during weathering are discussed as well as the geochemical changes occurring and an overall balance sheet for the weathering of these rocks is drawn up. The results obtained in this study are compared with those observed in the field.