The vesicles of an olivine-dolerite that occurs as a small outcrop near Portree in the Isle of Skye contain zeolites and some hydrated calcium silicates. These latter include tobermorite, xonotlite, gyrolite, and what is presumed to be a new member of the tobermorite group. An attempt is made to account for the sequence of crystallization of the minerals.

This process has been reinvestigated, mainly with X-rays, using an FeO-containing, fibrous variety (nemalite), and also a nearly pure specimen. The results confirm that the transformation is oriented, the c- and a-directions of the brucite becoming the normals to (111) and (11̄0) in the periclase. There is an intermediate, spinel-like stage; the spinel a-axis is parallel to, and twice as long as, that of the periclase. This stage is especially prominent when nemalite is heated in air or nitrogen, but is shown also by the nearly pure material. The nemalite shows also a further intermediate stage under certain conditions. A new hypothesis is proposed for the dehydration mechanism, in which the number of oxygen atoms per unit volume is ahnost unchanged in those parts of the crystal that are converted into periclase. The process is essentially one of cation migration, and the occurrence of the spinel-like phase is readily explained. Similar mechanisms possibly apply to the dehydration of other lamellar hydroxides and oxy-hydroxides (e.g. gibbsite, kaolinite) and of certain carbonates and other oxy-salts.

The parageneses of opaque minerals in three Assynt rocks are described. A biotite-diorite dyke-rock of Lewisian age is characterized by a primary igneous assemblage of Fe-Ti oxides, pyrrhotine, and pentlandite. Effects of metamorphism are recognized, particularly in the oxidation of ilmenite in a Lewisian epidiorite dyke-rock. Cromaltite contains a primary assemblage of oxide minerals together with a later hydrothermal sulphide assemblage. Evidence from the opaque minerals cannot be reconciled with a theory of limestone assimilation. The correlation of the distribution of Co, Ni, and Cu in the rocks with the opaque minerals present is considered.

Calculations are presented, based on modal and chemical analyses of titaniferous iron ore minerals from two localities (Skaergaard and Schmoo Lake). They show that Fe: Ti ratios are constant for granular aggregates of ilmenite and titaniferous magnetite formed at any one stage in the cooling history of the containing rock body. From this and other evidence it is concluded that the aggregates are the result of exsolution from original high-temperature cubic solid solutions. For the Skaergaard rocks, the problem of separately crystallized ilmenite, distinct from the granular aggregates, is also discussed.

It is shown that petrographic methods, using the microscope and micro-refractometer, can be a valuable aid in the identification of non-metallic inclusions in steel, even when their size is only a small fraction of a millimetre. Special ways of preparing the samples are given, and some of the methods used in examination are indicated. Natural chromite, corundum, merwinite, mutlite, quartz, rhodonite, spincls, and zircon are taken as examples of the minerals found.

Simple chemical procedures (colorimetric and gravimetric) for the determination of Co, Cr, Cu, Ga, Ni, P, and S in an iron meteorite or in the separated metallic phase of a pallasite are described; the minimum size of sample is discussed. A procedure for the quantitative removal of the metallic, sulphide, and phosphide phases from a stone or siderolite is described, and is applicable to the quantitative isolation of silicate and oxide inclusions from siderites (other than some very high in nickel).

Buerger (Zeits. Krist., 1957, vol. 109, p. 42) describes an algorithm for deriving data for the reduced unit cell from those obtained for an arbitrary crystal setting. It is shown that indices can be added to the algorithm so that one also derives the transformation matrix for the change of setting. Conversely, a known transformation matrix forms a set of instructions for using the algorithm to transform unit cell data, whether X-ray or morphological, from the initial to the final setting, One can thus use the algorithm to calculate the lengths of any unit cell vectors and the angles between them, and, using reciprocal cell data, to obtain any interfacial angles. Worked examples of these applications show that the proposed calculation method is shorter and simpler than those at present accepted.