Two specimens of almeriïte from the type locality have been examined by chemical analysis, d.t.a., and X-ray powder photography and shown to be identical with natroalunite. A little illite and kaolinite are present as impurities. X-ray powder data for natroalunite are presented.

The Younger Granites of Nigeria contain varied assemblages of iron-rich ferromagnesian minerals in which amphiboles are an important component. Eighteen of these amphiboles (separated from rocks belonging to nine complexes) have been chemically analysed and the results are presented and discussed. The amphiboles are shown to fall into two groups, a lime-alkali group (comprised of ferrohastingsite of general formula NaCa2Fe″4Fe‴Al2Si6O22(OH)2) and an alkali group (of general formula (Na, K, Ca)2.5–3.0(Fe″, Fe‴)5(Al, Si)3O22(OH)2). The alkali amphiboles are characterized by their extremely low magnesia content, by the presence of Li and F (both in significant amounts), and are of specialinterest because of the unusual amount of ZnO they contain. Optical properties of the amphiboles have been determined but it has not been found possible to use these properties to determine accurately the chemical composition of the alkali amphiboles. It is suggested that, according to current classifications of amphiboles, the analysed alkali amphiboles should be called riebeckitic arfvedsonites or arfvedsonites. The relationship between the hastingsites and the alkali amphiboles is not yet clear.

The cell parameters of fifteen arfvedsonites and four ferrohastingsites were determined using powder and diffractometer techniques and a least squares method of computation. Methods are proposed of distinguishing between calcium- and sodium-rich amphiboles, and between iron-rich and iron-poor varieties of these two groups, by their powder data. Within the arfvedsonite group the b parameter was found to increase with increasing Ca, Fe″, and (OH) and to decrease with increasing Na, F, and Li. The c parameter was found to decrease with increasing F and increase with increasing (Fe‴+Al+Ti). The parameters a, β, and a sin β all tended to increase with increasing Ca, Fe″, and F content. The cell volumes were found to vary with the b parameter. The ferrohastingsites were found to have much larger cell parameters than the arfvedsonites. An attempt was made to explain these variations from structural considerations.

Two pebbles of good quality nephrite from Kohat District are described and the possible origin of the stones is discussed. The discovery is of significance in relation to the unsolved problem of the origin of the raw material of Indian carved jade.

The problem of magnesian pyroxenes in acid liquids is considered in the light of new analyses of pyroxene and magnetite phenocrysts. It is suggested that the early precipitation of titaniferous magnetite, which will strongly deplete the liquid in iron, will decrease the iron:magnesium ratio of the pyroxene components in the liquid. Accordingly the iron:magnesium ratio of a pyroxene precipitating from an acid liquid may vary over a wide range depending upon the presence or amount of early magnetite.

Differential thermal analysis alone appears inadequate as a tool for distinguishing the many chlorite varieties; however, this process is capable of yielding much valuable information about the chlorites. The 7 Å septechlorite structure may be easily distinguished from the normal 14 Å chlorite structure. Two stages of dehydration, oxidation of ferrous iron, and structural collapse appear as endothermic and exothermic peaks on the D.T.A. chlorite curves. Septechlorites show only one, large dehydration stage, which leads directly to the structural breakdown. Iron oxidation accompanies the initial dehydration in both structural types, and the temperature at which dehydration begins is noticeably lowered by increasing ferrous iron content of the chlorite variety.

In the Carboniferous-Permian dyke-suite north of Loch Sunart, Argyll, a complete gradation is displayed from olivine-dolerite to camptonite. The dolerites are more numerous than the camptonites, and dykes of monchiquite are rare. A small number of minettes and allied lamprophyre types of Devonian age are also present. New analyses of biotite and diopside from a minette and of augite and hornblende from a camptonite are presented, with optical data, and the classification of the dykes briefly discussed.