The Maungaparerua halloysite deposit is located on the North Island of New Zealand some 210 km north of Auckland. The halloysite deposit was formed by hydrothermal alteration of rhyolite flow rocks. Superimposed on the hydrothermally altered halloysite is deep intensive surficial weathering resulting from the humid climate on the extreme tip of the North Island. The deposit has been drilled and the cores have been analyzed mineralogically and chemically. Drilling has shown that the deposit is circular or ovate and covers about 350 acres. The altered rocks contain about 50% quartz and fine amorphous silica and 50% of a mix of halloysite, kaolinite, and allophane with a small amount of plagioclase feldspar in the coarse fraction. The upper 8–30m, with an average of 15m, of the halloysite alteration deposit consists of relatively soft clay. Below this soft clay, which is the result of intense surficial weathering, the clay becomes hard and dense. The halloysite and kaolin from this deposit are mined and beneficiated using wet process techniques of dispersion, centrifugation, leaching, dewatering, and drying. The products are used as filler in paper, paint, and plastics and as a ceramic raw material for producing whiteware and fine china. This deposit is unique in that it contains a very high proportion of halloysite in the clay fraction. The detailed geology, mineralogy, geochemistry, and the physical properties of the clay will be discussed.

The adsorption of nitroxide spin probes on smectites solvated in liquids of greatly different polarity was studied using electron spin resonance (ESR) spectroscopy. Adsorbed probes demonstrate various degrees of restricted rotational motion and alignment at the silicate surfaces, depending upon the properties of the solvating liquid. The results are interpreted in terms of direct surface—molecule interaction modified by solvent competition effects. A fraction of the probe molecules is immobilized in many of the solvated clays because of small spacings between platelets. The data indicate lowered reactivity of surface-adsorbed molecules, especially in the case of hydrated smectites.

Hydrotalcite-like compounds [MgI − xAlx(OH)2]x+ [A2−x/2, mH2O]x−, where A2− is SO42− or CrO42− and x ≇ 0.25, were prepared by a coprecipitation method and their physico-chemical properties were studied by X-ray diffraction, thermal analysis, i.r. absorption spectra and acidity-basicity measurement.

The compounds including SO42− and CrO42− were analogous to an orthorhombic hydrotalcite and the lattice constants, a0 and c0 were 3.05 and 25.97 Å, and 3.05 and 26.48 Å, respectively. The crystallite size and strain in the 003 direction were 127 Å and 4.77 × 10−2 for the SO42− system or 83 Å and 6.60 × 10−2 for the CrO42− system, indicating a largely distorted microcrystallite. Two endothermic peaks observed at 240 and 455°C for the SO42− system and at 230 and 460°C for the CrO42− system are ascribed to the eliminations of interlayer water (mH2O) and structural water, respectively. The compound including SO42− formed MgO by calcination at 500°C and MgSO4 and MgAl2O4 by calcination at 800°C while the compound including CrO42− formed MgO at 400°C and MgAl2 − xCrxO4 at 800° I.r. study of the SO42− compound indicated that the bonding of SO42− was a bridge type. The highest acid and base strengths of the SO42− compound were H0 ≤ 1.5 and H− ≥ 12.2, the acidity and basicity being 0.3 and 0.1 mmol/g, respectively.

The adsorption of the cationic oxidized safranine S+ by a Na+, Ni2+ and Fe3+ montmorillonite has been studied with X-ray powder diffraction, u.v., visible and i.r. spectroscopy. In solution S+ may be protonated: S+, SH2+ and SH23+ have characteristic spectra in the 500–600 nm region where the clay structure does not absorb. In the Na+ as well as in the Ni2+ and Fe3+ clays, the adsorption of S+ is a cation exchange process accompanied by the protonation of the adsorbed dye such as variable concentrations of M+ (Na+, Ni2+ or Fe3+), S+ and SH2+ are simultaneously present. Protonation activity decreases from Fe3+ to Ni2+ and Na+, being the protonation site the amine group as shown by i.r. In the interlamellar space it seems that a SH2+.. S+ association exists that could be described as a sandwich structure 6.5 Å thick.

Clay materials separated from estuarine sediments in Louisiana exhibit a selectivity for exchangeable calcium in laboratory experiments. The studies were conducted at 25°C and 60°C in mixed calcium and potassium chloride solutions in which the equivalent fraction of potassium varied from 0.12 to 0.54. Calcium selectivity was observed to increase with an increase in the equivalent fraction of potassium in the external solution and the temperature. The results suggest the possible importance of ion exchange reactions in the regulation of calcium availability during early diagenetic reactions in sediments.

From 2 to 28% opal-cristobalite was isolated from the 2–20 µm fraction of rhyolitic and andesitic tuffaceous pyroclastics from the Island of Honshu, Japan, where it had been formed in hydrothermal springs at temperatures of ∼25–170°C as calculated from the oxygen isotopic ratios (18O/16O). Three of the isolates gave X-ray powder diffractograms with strong peaks at 4.07 Å. Two of these also had very weak peaks at 4.32 Å indicative of the presence of traces of tridymite. The fourth isolate had a strong 4.11 Å cristobalite peak and a very weak 4.32 Å peak. The morphology, determined by the scanning electron microscope, varied with the formation temperature indicated by the oxygen isotopic ratio (δ18O), from spheroidal and spongy for the opal-cristobalite formed at ∼25°C (δ18O = 26.0‰) in contrast to angular irregular plates and prisms for that formed at ∼115°C (11.9‰), ∼135°C (7.9 ‰) and ∼170°C (6.8 ‰). The differences in δ18O values are attributed to variation in hydrothermal temperature, but some variability in oxygen isotopic composition of the water is possible. The field-measured temperatures related roughly with the calculated fractionation temperatures except in one site, while the contrast in cristobalite morphology related well to calculated low and high fractionation temperatures. Low-cristobalite of hydrothermal origin in New Zealand (δ18O = 9‰) had characteristic rounded grains with some evidence of platiness. Co-existing quartz grains (δ18O = 10‰) showed more subhedral and irregular prismatic morphology.

The electrical conductivity of a colloid-water-electrolyte system increases with the frequency of the applied alternating electric current. The phenomenon is referred to as conductivity dispersion. This paper reports on the effects of electrolyte type, electrolyte concentration, and water content on the dispersion characteristics of kaolinite, illite, and silty clay soils, with emphasis on the mechanisms governing the dispersion phenomenon. It was observed that magnitude of conductivity dispersion increases with a reduction in water content, electrolyte concentration, and cation-exchange capacity of the clay. The type of ions influence the electrical dispersion through their size and mobility. Frequency effect increases as the hydrated radius of the counterions associated with the clay surface increases. Conductivity dispersion is explained primarily in terms of counterion/co-ion ratio in the diffuse double layer. Increase in the ratio of counterions to co-ions is an indication of a larger contribution to conduction by counterions than by co-ions, which in turn results in a larger frequency effect. Although diffusion coupling has an important role in the electrical dispersion characteristics of clay—water—electrolyte systems, other coupling phenomena, particularly electro-osmotic coupling, plays a significant part.

0.5 molal iron(III) chloride solutions were hydrolysed at room temperature by base additions in the range OH/Fe mole ratio 0–2.75. After an ageing period the hydrolysed solutions were used to produce amorphous hydroxide gels from which crystalline products were grown at 65°C, at low pH or high pH. Examination of crystal composition and morphology and comparison with similarly treated nitrate solutions showed that the nucleation of hematite and goethite is inhibited in chloride containing solutions, which allow growth of small rod shaped β-FeOOH to predominate or occur exclusively in gels at pH 1–2. The addition of seed crystals of hematite and goethite allows competitive growth of all three minerals. The transformations β-FeOOH → α-Fe2O3 and β-FeOOH → α-FeOOH at pH 1–2 proceed by dissolution and reprecipitation and are promoted by adding seed crystals.

Chlorite and illite are the major clay minerals in silicate assemblages from a rock salt bed in the Vernon Formation (Upper Silurian) at Retsof, New York. Textural features and Br content of the salt indicate precipitation from shallow marine brine with no subsequent postdepositional recrystallization. Sample mounting procedure for electron microprobe analysis involves clay particle dispersion, sedimentation, and transferral to a planar silver print surface. The 001 face of the flake, rather than the conventional polished plane, constitutes the analyzed surface. Microprobe analysis of the chlorite (80 grains from four samples) yields a mean aggregate Mg-rich clinochlore composition of

$$(M{g_{4.51}}Fe_{0.23}^ + A{l_{1.21}})(A{l_{1.09}}S{i_{2.91}}){O_{10}}{(OH)_{8,}}$$

$${{\rm{K}}_{0.85}}(A{l_{1.61}}Fe_{0.20}^{3 + }M{g_{0.23}})(A{l_{0.76}}S{i_{3.24}}){O_{10}}{(OH)_2}$$

Diagenesis effected improved crystallinity and undoubtedly involved isochemical recrystallization of the bulk silicate assemblage. Metasomatism of the assemblage during diagenesis, however, appears to be negligible.