The Wairarapa Valley hypersthene-olivine chondrite, found about 1863, has been analysed with the following result: SiO2 35·72, TiO2 0·11, Al2O3 2·91, Cr2O3 0·48, FeO 12·42, MnO 0·28, MgO 23·28, CaO 1·73, Na2O 0·96, K2O 0·20, P2O5 0·31, Fe 12·61, Ni 1·50, Co 0·04, FeS 5·46, Cl 0·07, H2O+ 1·05, H2O− 0·48, less O for Cl 0·03; total 99·58 %. D. 3·65. The phases present are kamacite, taenite, plessite, troilite, magnetite, chromite, olivine Fa16, bronzite Fs15, possibly enstatite, plagioclase An25, and (?) maskelynite An9. The structures of the silicate phases and those disclosed by etching the metal phase are illustrated and described.

The phenocrysts of four porphyritic obsidians from Pantelleria have been analysed chemically, together with the residual glasses (liquids). Three new analyses of anorthoclase (one partial analysis), two of sodic ferrohedenbergite, one of fayalitic olivine, and two of cossyrite are presented together with their optical properties, and the relationship of these phenocrysts to their liquids is considered.

The experimental studies in the system NaAlSi3O8-KAlSi3O8-SiO2-H2O show that for synthetic liquids of similar composition to the normative salic constituents of the pantelleritic liquids, a potassic alkali feldspar crystallizes, whereas in the pantelleritic liquids phenocrysts of anorthoclase (Ab67–Ab61) occur. It is suggested that sodium metasilicate, which appears in the norms of all the pantelleritic liquids, may be responsible for the divergence in trend between the synthetic feldspar-liquid tie-lines and the pantelleritic feldspar-liquid tie-lines.

A detailed electron and X-ray diffraction study of a suite of nephelines from a wide range of paragenetic environments indicates that, in all cases studied, additional weak maxima of scattered intensity are present. Similar intensity maxima have previously been observed and described in an isolated case by Sahama. Thermal treatment at temperatures as low as 200° C causes these maxima to become noticeably diffuse, implying a structural transformation.

A zoned plagioclase crystal from a magmatic quartz-diorite shows two generations of pericline twinning: one growth twinning, the other glide twinning. Plotting the angle of the rhombic section against composition for each set of twins gives curves indicative of an intermediate structural state with respect to the theoretical curves determined by Smith (1958). The curve for the growth twins is closer to the high structural state than that for the glide twins and supports the primary origin of the former. This curve is believed to fix approximately the lowest structural state at which primary pericline twinning can develop in magmatic rocks. The lack of coincidence of the curves for the two generations of twinning indicates partial inversion prior to formation of the glide lamellae, while the position of the curve for these secondary lamellae suggests a genetic relation to inversion. Both rhombic sections are probably relict with respect to the present structural state. The form of the curves confirms the general accuracy of Smith's curves for the maximum high and low structural states.

The accurate determination of α:[001] and 2V in members of the aegirine-augite series often presents difficulties owing to strong absorption and dispersion, especially as high angles of tilt on the universal stage are often involved. Both of these angles depend on the location of α, and this operation is the one most subject to error.

An alternative procedure is the determination of A:[001], the angle between an optic axis and [001]. This angle is very easily and accurately determined and varies systematically with composition. It can be derived from the values for α:[001] and 2V, while conversely values of α:[001] and 2V can be obtained from A:[001] by reference to standard curves.

The occurrence of tridymite, now inverted to quartz, in a craignurite (allied to granophyre) from Craignure, Mull, is described. An account of the field occurrence and petrology and a new analysis of the craignurite are given. The significance of the occurrence of tridymite is discussed in the light of recent experimental studies.

Aluminium oxides occur widely in soils and are of considerable pedological significance. The ageing of alumina gels, prepared from aluminium chloride and ammonia, into crystalline hydroxides has been investigated using thermal, X-ray, infra-red, and electron-microscope techniques. At room temperature ageing is more rapid at high pH values. The structure of the original gel particles appears to resemble boehmite and ageing causes the formation of bayerite with small amounts of gibbsite. The morphology of the various mineral types is considered and a mechanism of ageing suggested.

Powellite, appearing to be of primary late-magmatic origin, has been found associated with analcime, apophyllite, and calcite in a geode in phonolite. Data are: D 4·40, ε 1·984, ω 1·971, a 5·20 Å, c 11·43 Å, CaO 27·8, MoO3 61·8 (av.), WO3 11·4 (av.).

A cutting technique, based on the use of carefully prepared plan projections, has been evolved for the making of unlimited numbers of accurate wooden replicas of natural crystals.