The alteration of thirty-nine trioctahedral micas to vermiculite has been characterized by the K level, which is determined by repeated measurements of the stationary K concentration in the altering solution and provides a practical way of comparing the sensitivity to alteration. A calculated regression equation allows the K level of a sample to be predicted from its chemical composition. The model proposed for the alteration reaction outlines the physico-chemical meaning of the K level, with its experimental and theoretical limitations.

The synthesis of magnesium smectite from heated slurries of magnesium hydroxide, silica and lithium fluoride proceeds through ready formation of torroidal structures visible under the electron microscope. These are associated with the synthesis of a smectite-like material with, however, only half the expected requirement for silica. True smectite only forms significantly with Si/Mg ratios > 1 and reaction times (at reflux) > 1-3 days.

Specimens of palygorskite from Warren Quarry, Enderby, Leicestershire, have been studied in the laboratories. The mineral is found in dioritic rocks in association with angular dolomitic rock fragments as the filling material of a joint, the walls of which are sometimes lined with calcite and dolomite. Palygorskite occurs as 3-10 mm long bundles of fibres, 0·03-0·1 μm wide. X-ray diffraction data indicate that the mineral may occur in the monoclinic form. The structural formula for the half-unit cell is Si8(Al1.89Fe0.053+Ti0.01Mg1.99)O20(OH)2(OH2)4 3·61 H2O.Ca0.07. Data obtained from differential thermal and infrared analyses are comparable with those for palygorskite in the literature, but the six-sided transversal cross-section of the fibres as revealed by electron microscopy is unexpected. The mineral was formed after the deposition of the overlying basal Triassic rocks when ground waters penetrated cracks in the dioritic rocks, causing Si and Mg to be released there and above the unconformity.

Sorption of molecular amines by montmorillonite involves protonation of the amine group and hydrolysis of the interlayer cation. Sorption and subsequent desorption of amines may render some of the interlayer cations non-exchangeable, thus causing partial 'chloritization' of the montmorillonite. The effect is stronger with interlayer Al than Ca ions and depends upon the amine sorbed.

Examination of field samples shows that the alteration of the bentonite beds of Wyoming and Montana near the surface to produce high-quality, highswelling, commercial bentonites is analogous to pedocal soil development. The near surface bentonite has undergone extensive calcification, and in some zones it is so heavily altered as to diminish its swelling properties. These low-swelling bentonites can be activated by conventional soda-ash additions. The naturally high-swelling materials have undergone only partial calcification and do not require soda-ash modification. The relatively unaltered 'grey' or 'blue' bentonites have undergone little or no calcification. The latter have the highest Na to Ca ratios, are non-swelling, and do not respond markedly to soda-ash additions. Such low-swelling materials will respond to calcium-activation with markedly improved physical quality parameters of flocculation as measured by Marsh Funnel and Fann viscosimeter. The study indicates that vast reserves of low-swelling bentonites in Montana-Wyoming may be susceptible to controlled calcium activation and expanded commercial utilization.

An X-ray diffraction method for the estimation of quartz is described using rock powder pellets originally prepared for X-ray spectrometry, correcting the X-ray intensities for mass absorption. A coefficient of variation of 3·8% is claimed; 95% of all estimates fall within ± 5·5%.