The more firmly held water which is directly co-ordinated to the exchangeable cations in smectites is clearly distinguished by infra-red spectroscopy from the more labile water in outer spheres of co-ordination. Li+, Ca2+ and Mg2+ retain both types of water to higher temperatures than do K+, Na+ and NH4+, and the former group give stable monohydrates in saponite which are probably not completely decomposed till 400–600°C. K-, Li- and Na-saponite rehydrate completely after heating, but NH4-, Mg- and Ca-saponite are irreversibly dehydrated at 600–700°C, by which temperature NH4+ is also decomposed. NH4-, Li- and Mg-montmorillonite fail to rehydrate after heating to 350°C, and changes in their spectra indicate interaction between the exchangeable cations and the lattice. Decomposition of NH4+ gives H-montmorillonite, but the products from Li- and Mg-montmorillonite are also acidic, and give spectra similar to that of H-montmorillonite. Na- and Ca-montmorillonite do not rehydrate after heating to 500–550°C, and K-montmorillonite rehydrates only partially in the range 350–550°C. Dehydration of saponite and montmorillonite at low temperatures causes changes in lattice vibrations which are reversed on rehydration. The spectra of the products of dehydroxylation of montmorillonite and saponite are slightly affected by the exchangeable cation originally present.

In Scandinavian podzols a swelling dioctahedral mineral, probably derived from dioctahedral mica and iron-rich chlorite, has been found in the clay (<2µ) fractions from A2-horizons. This mineral, or group of minerals, is shown by X-ray examination and differential thermal analysis to be of a vermiculite-smectite type, thus making the differentiation between vermiculite and smectite still more problematical. The pretreatment of the samples and choice of interlayer cations is shown to be of great significance for the identification of soil clay minerals.

A study has been made of the relative abundance of clay minerals in about a hundred samples of sedimentary rocks of Pre-Cambrian, Cambrian, Upper Carboniferous, Permian, Triassic, Jurassic, Lower and Upper Cretaceous and Tertiary formations in the geosynclinal basin of the (Tethys) Himalayan zone. Chlorite predominates in the Cambrian sediments and illite in the Permo-Carboniferous to Tertiary sediments; kaolinite is a minor variable component and montmorillonite is scarce. The high-chlorite Cambrian sediments are rich in dolomite and gypsum and contain predominantly plagioclase felspars, whereas the high-illite Triassic and Eocene sediments are rich in alkali felspars, the dolomite is low and gypsum is absent. In the (newer) Tertiaries of the Middle Miocene age (fluviatile deposits in shallow freshwater basin) illite, kaolinite and montmorillonite are present in almost equal amounts but chlorite is undetectable. The predominance of kaolinite and montmorillonite in the sediments of the Lower Pleistocene period indicates the existence of a distinctly fluviatile facies in the basin of deposition. Interstratified illite-montmorillonite and montmorillonite are characteristic of Siwalik (Miocene) sediments and of Spiti-shale type Jurassic sediments.

A description and details of performance are given for a differential thermal apparatus which has been developed at the C.S.I.R.O. Division of Coal Research for use in studies of the mineral matter in coal. An important feature of the design is the block assembly unit, which fits into a vertical furnace, and comprises a stainless steel block in which are the three sample wells and three insulated chromel-alumel thermocouples. The output from the differential thermocouples is applied to a simple transistorized D.C. amplifier before being passed to a recorder which traces simultaneously against time the temperature difference and the temperature. Features of the apparatus which have proved especially attractive in research on coal are its automatic operation, ease of maintenance, and base-line stability. Reproducibility of results is good.

Mineralogical compositions have been calculated from a number of average analyses of shales and clays using the scheme of Imbrie and Poldervaart (1959). The average shale comprises 59 per cent. clay minerals, 20 per cent. quartz and chert, 8 per cent. felspars, 7 per cent. carbonates, 3 per cent. iron oxide minerals, 1 per cent. organic matter and 2 per cent. other minerals. Illite predominates among the clay minerals.

Extensive deposits of red glacial drift and lacustrine clay occur along the east coast of Aberdeenshire and constitute the parent materials of important agricultural soils. The mineralogy of lacustrine clay at Tipperty, Aberdeenshire, has been determined by X-ray, differential thermal, and optical methods. General relationships between the mineralogy of this soil parent material and that of other red drifts in the vicinity are discussed with reference to the glaciology of the region. It is suggested that these red drifts were transported from the bed of the North Sea and not from Strathmore.

It has frequently been suggested that there is more than one structural type of montmorillonite, and the investigations of Grim and Kulbicki have supported this concept. From the data given by these authors, thirty-six characteristics have been selected and the montmorillonites compared using a multivariate analysis computer programme. The results do not support the hypothesis of two types of montmorillonite, but indicate a random distribution of the samples in an n-dimensional space.

The fine structure of the X-ray absorption spectrum observed on the high energy side of the iron K edge has been recorded with a modified commercial single-crystal X-ray spectrometer. Metallic iron samples exhibited no detectable fine structure, whereas Fe3+ in ferric oxide and Fe2+ in ferrous ammonium sulphate and ferrous sulphate produced significant fine-structure peaks due, presumably, to 1s→4p and 1s→5p electron transitions. The apex of the 1s→4p peak and the minimum between the two peaks were shifted to lower energies by the Fe2+ samples, and the corresponding apices and minima on fine-structure spectra of samples containing Fe3+ and Fe2+ were shifted by an amount which was approximately a linear function of composition. These observations have led to the development of an analytical procedure for the determination of ferric (or ferrous) iron in dry, ground or sedimented clay mineral samples. The lower limit of total iron concentration in the clay sample to which the method is applicable is approximately 1 per cent. The procedure appears promising as an indicator of the oxidation-reduction potential of the geological environment with which the clay mineral may have been in equilibrium, and as a tool of more general geochemical utility.

The inference of Gruner that unsatisfactory powder photographs of vermiculite resulted from distortion of the structural planes by grinding has not been substantiated. The unit cell parameters of a true vermiculite were found to be ao = 5·24± 0·02Å, bo = 9·17 ± 0·02Å, co = 28·60±0·05Å, β = 94° 36′ ± 24′, while the structural formula worked out as (Mg2·37, Fe3+0·37 X0·26) (Al1·28, Si2·72)O9 (OH)3·4H2O, where X represents the remaining octahedral cations. The determined density of the thin flakes was 2·28 g/cm3 and taking this value along with the volume of the unit cell (1370Å3) and the “molecular weight” calculated from the above formula, the number of formula units per unit cell worked out as Z=4·03. Some ‘vermiculite’ samples contain small groups of mica layers, but the non-basal mica reflections are not observable. The structures of these interstratifications and also of interstratifications containing chlorite are considered. Electron micrographs of vermiculite and the interstratified minerals are presented.

The effect of the firing schedule on some physical properties of a group of Etraria marls has been studied. Of particular interest are the thermal expansion and moisture expansion of the clays which reflect mineralogical changes occurring during the firing process.

The occurrence of metahalloysite ‘nodules’ in the silica sand pocket deposits near Brassington, Derbyshire, is recorded for the first time. The geological surroundings are briefly described in an attempt to arrive at an explanation of the genesis of the ‘nodules.’ The history of attempts to work the deposits as china clay in the 18th century is included.

Chamosite has been identified as a regular member of the suite of minerals constituting the Lower Ecca shales in Natal. In this deposit, chalybite, Fe-chlorite and illite are all found to be secondary to the chamosite component which serves as the principal mineral host for iron, even in beds containing as little as 2·25% Fe. Aspects of composition, fissility and origin are discussed.

Gibbsite, the dominant mineral in red and yellow earths from Mount Zomba in southern Nyasaland, is derived directly from orthoclase and acid plagioclase (albite-oligoclase). The bauxitization apparently took place at an early stage in the history of the mountain. The evidence suggests that kaolinization succeeds bauxitization in the sequence of weathering, and is related to present-day weathering conditions.

Ten raw materials, typical of those used by the majority of British manufacturers of structural clayware, are shown to cover a wide range of mineralogical composition. Kaolin, mica minerals and quartz are always present, though their relative percentages vary widely. Other minerals which may be present in more than trace amounts, are montmorillonite, dolomite, calcite, sepiolite and chlorite. The correlation between the mineralogy of a raw material and its physical characteristics is reasonably good; the presence of montmorillonite, in particular, can have a marked effect. The importance, however, of the degree of compaction of the raw material (largely a function of geological age) is emphasized. Variations in clay mineralogy appear to affect firing behaviour less than variations in the content of alkaline earths, where present.

A new method is described for determining in shales the amount of sulphides that dissolve in dilute hydrochloric acid. The samples are treated with hydrochloric acid under vacuum, and the hydrogen sulphide evolved is absorbed in potassium hydroxide and titrated with potassium permanganate. The analytical results are expressed as FeS.

Certain minerals in soil clays may be directly estimated from diffraction line intensity and the mass absorption coefficient of the sample to the radiation used. The main advantages of the method described are that no internal standards or calibration charts are required, and any diffraction line of the component to be estimated may be chosen. The results obtained compare favourably with chemical determinations. Orientation of particles during sample preparation makes the estimation of some minerals very difficult. The uncertainty involved in choosing the background level under a diffraction line is the chief source of error in estimating small amounts of very fine-grained minerals.

The mineralogical composition of the clay, silt and sand fractions from soil profiles representative of four of Ceylon's major soil groups have been determined using X-ray, differential thermal, optical and chemical methods. The results show that the mineral assemblages in these fractions can be correlated with the pedogenesis and the degree of maturity of the profile.