The compound Li2Zr(WO4)3 has been synthesized. It has the monoclinic wolframite-type structure with cell dimensions a 4·78Å, b 5·70 Å, c 4·96 Å, and β 92° 10′. The univalent and tetravalent cations are randomly arranged in the divalent cation sites in the wolframite-type lattice.

Determinations of Cu in separate phases of three olivine-hypersthene and one olivine-bronzite chondrites show that it is very strongly concentrated in the taenite; appreciable amounts are present in the olivine, less in the pyroxene plus plagioclase; it is probable that the copper found in the ‘unattracted, attacked’ fraction is present as metallic copper, and that very little is present in the sulphides.

A re-examination of twelve specimens of the Gibeon meteorite has established that the meteorite is basically an octahedrite but has, in several irons of the meteorite, lamellae of kamacite of early origin parallel to the cube. Lamellae containing daubréelite, predating twinning and kamacite exsolution, are common parallel to the cube and rare parallel to the octahedron. A survey of other features failed to suggest any definitely correlated with the anomalous kamacite lamellae.

Garnets undergo readjustment of ion-assemblages under external mechanical and thermal stresses; this adjustment favours those paths that annul the very cause to which it is due. Metal ions in garnets being replaceable, with rising metamorphism garnets become reluctant to accommodate ions of larger ionic radii.

Data from recent literature on chemical analyses of garnets from rocks belonging to different grades of regional metamorphism reveal that the (FeO + MgO) content of garnet varies linearly with (CaO + MnO) content. As the Fe/Mg ratio does not vary appreciably, a fair estimate of metamorphic grade can be made from a knowledge of (CaO + MnO) or of (FeO +MgO) individually or even, with less confidence, of FeO or MgO alone. From the study of the available data it is found that (CaO + MnO) and (FeO + MgO)/(CaO + MnO) provide the best indicators of progressive metamorphism. Cell edges of garnets decrease progressively with increasing metamorphism and this may also be used as a fairly good index of metamorphism. When cell edges are plotted against (FeO + MgO)/(CaO + MnO), a hyperbolic curve is obtained.

The Benue trough is a graben structure containing folded Upper Cretaceous sediments. Mid-Tertiary to Recent rift-valley type vulcanicity in and near the trough was mainly basaltic (in the north at least), salic lavas being now represented mainly by a few eroded plugs. The Nigerian rocks are regarded as a practically extinct sub-province within a larger Gulf of Guinea alkaline province, dominated by the voluminous and still active vulcanicity of the Cameroun rift. The two structures have the same trend as other graben features further south along Africa's western margin.

Large sodic plagioclase crystals in a basalt plug within the Nigerian sub-province have rounded edges and more calcic overgrowths. They probably crystallized at deep crustal levels but are unaccompanied by any of the mafic phases that normally crystallize from basalts under high pressure. However, spinel crystals and olivine nodules found in a nearby plug indicate that the complementary mafic assemblage may be found not far away. Sparse published data on phenocrysts and inclusions in the Jos Plateau lavas offer some support for this suggestion.

Crystallization of sodic feldspars in basalt may have a bearing on the independent genesis of salic liquids, while apatite and magnetite inclusions in them suggest a possible link with carbonatites.

Originally described in phonolitic rocks from the Dunedin district, New Zealand, ameletite was considered by Marshall (1929) to be a chlorine-bearing sodium aluminium silicate, probably a feldspathoid, and later, a zeolite of unspecified composition. Optical, X-ray, and chemical data on several ‘ameletite’-bearing felsic volcanic rocks from the type area indicate that material previously designated as ameletite is variously nepheline and mixtures of sodalite, analcime, phillipsite, and nepheline. Criteria thought to be characteristic of ameletite are discussed.

A rapid method for determining the mode of a four-component powder (microcline, orthoclase, plagioclase, and quartz) was sought to aid the interpretation of geochemical results. An accuracy of about ±5 % (absolute) was required. Three methods were tried : point counting proved too long as well as destroying the sample; infra-red spectroscopy was not sufficiently accurate for this particular type of rock powder; X-ray diffraction proved the most rapid and, although less accurate than point counting, was within acceptable limits and had the advantage of giving additional information about the composition of the feldspars.

This paper describes a harmotome from the Korsnäs mine in Finland, which occurs in the same open cavity as the yellow apophyllite previously reported in this journal. The harmotome is always twinned according to the morvenite and Marburg laws. Chemical composition, optical properties, X-ray powder pattern, and single crystal data are given.