The changes in X-ray diffraction patterns of layer silicates which result from dry heat-treatments below 550°C have been studied and the results are tabulated in order of increasing temperature at which these changes are observed; the structural implications are briefly considered. In order to evaluate the effects of composition, particle size and disorder, synthetic clay minerals have been used in addition to natural clays. This summary of X-ray data may be of value in the identification of clay minerals in mixtures.

Seven brickmaking clays from various geological horizons have been studied by differential thermal and X-ray methods. The minerals detected included kaolinite, illite, montmorillonite, chlorite, swelling chlorite, calcite and quartz, and rough estimates were made of the quantities present. For the same clays, deformation-under-load was measured at four different heating rates, and strength and water absorption were determined on fired blocks. No correlation between the firing properties and mineralogical constitution is observable.

The question is raised as to what extent a study of the clay mineralogy enables the detailed ceramic behaviour of a clay to be predicted. It is indicated that the behaviour of a clay in an industrial process is often controlled by other factors, such as particle size distribution of the clay minerals and firing conditions which must, therefore, also be taken into consideration.

A number of different commercial vermiculites have been examined and it has been found that the exfoliable minerals can be divided into three main groups; those which give a 26 Å spacing on an X-ray diffraction pattern, those which give a 14 Å spacing, and those which give various spacings and are partially dehydrated. All are mixed-layer minerals of one type or another, but all have some vermiculite layers in their constitution. The expansibility of these minerals is not linked with their structural types, but there is an indication that the largest expansion is associated with the occurrence of hydrobiotite and the lowest expansion with the occurrence of true vermiculite.

A lithium mica extracted magnetically from china stone is compared chemically and by X-ray methods with known lithium micas. This comparison shows a strong resemblance between the Cornish mica and zinnwaldite from the Zinnwald.