A neutron activation analysis of one of the crystals of ‘monalbite’, which was monoclinic at room temperature, shows that it contains a large proportion of potassium. It is thus not a polymorph of pure NaAlSi3O8. The contamination occurred by transfer of K through the atmosphere of the furnace from potassium-bearing ceramic materials.

A new variety of chrome mica containing V2O3 and TiO2 has been investigated by X-rays. It is shown that the crystals of this mica are monoclinic with a= 5·25 Å, b = 9·03 Å, c = 20·11 Å, β = 96·00′, space group C 2/c. Comparison of the intensities of the X-ray powder lines of this new variety of mica with that of pure muscovite may indicate structural changes. The optical properties and chemical composition of the mica are described.

A 230 g kaersutite xenocryst from basalt at San Carlos, Arizona, has the composition SiO2 40·10 %, TiO2 4·44, Al2O3 14·53, Fe2O3 3·24, FeO 10·05, MnO 0·14, MgO 11·00, CaO 11·06, Na2O 2·99, K2O 1·62, H2O + 0·73, H2O − 0·10; D = 3·28; α 1·680, β 1·700, γ 1·715; a 9·858 Å, b 18·063 Å, c 5·315 Å, β 105° 14′. Kaersutite occurring as xenocrysts in basic volcanic rocks and tuffs, and as a phase in garnet-pyroxene xenoliths from such rocks, is probably of upper mantle origin, and may be the important potassium-bearing phase in this region.

The principal reflectivities of orthorhombic calcium monoferrite have been determined at 500 Å intervals from 4500 to 6500 Å. A small amount of calcium hexaferrite was shown to be present by electron probe examination.

Two groups of meteorite finds in separate areas of the Nullarbor Plain are reported. It is suggested that the grouping is due to the fact that these are areas in which a family of rabbit trappers operates: these people have made most of the finds. There is, however, one shower of 71 small meteorites represented. Several arrivals on earth are represented by each group. The meteorites are described and it is shown that several distinct types are represented. Two quite different ureilites have been identified—only the fourth and fifth ever discovered in the world. Analyses are given for these rare carbonaceous achondrite meteorites. The remainder of the stones are olivine-hypersthene and olivine-bronzite chondrites. The whole question of the reason for the profusion of meteorite recoveries now being made on the Nullarbor Plain is briefly discussed.

An ideal solution model has been used to calculate the effect of the substitutions on the stability fields of the Al2SiO5 minerals. The results show that divariant assemblages of andalusite+sillimanite and sillimanite + kyanite solid solutions can coexist over ranges of 0·1 to 0·4 kbar at 527° C, but that kyanite+andalusite would be stable over a much narrower range. On adding (Fe, Mn)3+ to the system, the andalusite/sillimanite curve can be considered to rotate about the invariant point, first eliminating the sillimanite field, and then penetrating the kyanite field. Wide zones of viridine+sillimanite and viridine+kyanite are thus formed.

In view of the ease with which epitaxial nucleation occurs in the Al2SiO5 system, it is considered that extensive metastable growth of andalusite, sillimanite, and kyanite is improbable in nature. Metastable persistence is likely to occur in dry systems, or in the presence of an ‘armour’ of the stable phase, but reaction of millimetre-sized crystals should be completed in geologically short times when aqueous or silicate liquids are present. The combination of the effects of metastable persistence and solid solution seems adequate to account for essentially all the examples of kyanite + sillimanite and kyanite + andalusite, and for many sillimanite +andalusite assemblages. In addition, if small supersaturations develop during metamorphism, simultaneous growth of andalusite + sillimanite could occur over a restricted temperature range.

The infra-red spectrum of untreated thaumasite Ca3H2(CO3/SO4)SiO4.13H2O, as well as the spectra and X-ray diffraction patterns of thaumasite heated in air at 200, 360, 550, 725, 800, 900, and 1150° C were investigated. The release of CO2 and H2O upon heating was followed. It was established that thaumasite changes between 200 and 550° C to a glass-like, amorphous state. Ca2SiO4-polymorphs and anhydrite are formed upon heating at temperatures up to 800° C. From 900° C calcium silicosulphate and anhydrite are the thermal decomposition products. These results are used in the assignment of the IR-absorption bands under 1400 cm−1 of untreated thaumasite, which are shown to be of a composite nature, i.e. attributable to overlapping vibrations of both sulphate and silicate tetrahedra.

These minerals indicate strongly reducing conditions as well as extremely low sulphur fugacities within the Newport pallasite. They all formed at low temperatures (upper limit 580° C) and in the solid state. This is the first reported occurrence of mackinawite and pentlandite from a pallasitic meteorite; Cu is known from only one other pallasite. Microprobe analyses of a large Cu grain indicate its composition as 98·6 ± 0·5 %, Ni 2·0 ± 0·5, Fe below the limit of detection (∼0.3).

Measurements from powder diffraction patterns recorded at temperatures up to 950° C for the supposed equilibrium forms of albite synthesized at 800°, 900°, and 1000° C by MacKenzie (1957) indicate that only the form synthesized at 1000° C becomes monoclinic. Single-crystal measurements on heated pure natural albite (Ab99·26) show that it becomes truly monoclinic, both in geometry and intensity distribution, at 930° C, the same temperature as for the highest-temperature synthetic form. These experiments were carried out in conditions that exclude possible contamination by potassium.

Earlier palaeomagnetic studies on the Dunedin volcano showed that a portion of the sequence is reversely or anomalously magnetized. Some of the rocks used for palaeomagnetic study were subsequently classified into groups according to their thermomagnetic behaviour (unpublished work).

Cell dimensions and Curie-point curves have been measured for oxides separated from representative rocks of each group. The oxides are mostly homogeneous titanomagnetites containing between 40 and 55 mol. % of ulvöspinel, with a generally small degree of late low-temperature alteration. X-ray and thermomagnetic data also suggest that there was some early oxidation to titanomaghemite, probably during cooling.

The thermomagnetic behaviour of rocks classified in the different groups is attributed to variable oxidation of the titanomagnetite during thermomagnetic treatment. The high Curie points of rocks used for palaeomagnetic studies may often be due merely to oxidation of titaniferous magnetite and not to nearly pure primary Fe3O4. Since there is insufficient oxidation in the lavas examined for any currently accepted self-reversal process to have been operative, the reversely magnetized part of the Dunedin sequence was probably erupted during a reversed polarity epoch, possibly between about 13 and 11 million years ago.

The basanitic lavas contain minor amounts of chromiferous spinel, as inclusions in silicate phenocrysts and as cores to separate microphyric titanomagnetite; its significance is briefly discussed.

Electron-microprobe scanning pictures and quantitative analyses of the nickel silicide perryite in the Kota-Kota and South Oman enstatite chondrites are given. Comparative data for the narrow perryite lamellae in the Horse Creek iron meteorite are included. Perryite in these meteorites lies within the limits 75–81% Ni, 3–7 % Fe, 12–15 % Si, 2–5 % P.

The principal data about the fall and the distribution of the fragments of the Assisi (Perugia, Italy) meteorite are collected. A fragment of the stone, weighing 146·5 g, preserved in the British Museum (Natural History) (B.M. 63621), is described in some detail. Crust morphology, mineralogical composition, and structure are studied. Optical data are established by microscopical analysis of five thin sections and two polished surfaces. Compared with electron-probe analysis, they are found in good agreement. Assisi is an olivine-bronzite chondrite, H group, with characteristic features of metamorphism.

In view of recently reported microtektites in deep-sea sediments north-west, south-west, and south of Australia, attention is drawn to the occurrence of minute forms of hay-silica glass among the products of incineration of opal-bearing vegetation in haystacks, and to the minute forms of volcanic glass ejected in lava fountains. These terrestrial micro-forms of glass have properties within the range of those for the fossil glassy bodies named ‘microtektites’. It is possible that the fusion of opal contained in silica-accumulator plants during fierce, prehistoric forest, bush, and grass fires in Australia generated micro-forms of glass that became readily airborne and drifted away in up-currents. Carried by the south-east Trades, they would ultimately descend over the Wharton Basin in the Indian Ocean. Strong to violent northerlies and north-easterlies (Brickfielder Winds) would carry them over the ocean south and south-west of Australia. Thus they could contribute to the deposits of bodies of glass regarded as microtektites in deep-sea sediments. Many microbodies of glass in the Wharton Basin could have had their origin in the Javanese volcanic eruptions.

The Bencubbin meteorite and some of its enclaves have been studied in thin section under transmitted light: supporting X-ray diffraction and chemical data have been supplied by the Smithsonian Institution, Washington. These results show the host material to consist of clinoenstatite and a little olivine (both nearly pure magnesian varieties) set in an opaque (cryptocrystalline ?) base, which is, in turn, enclosed in a mesh-work of nickel-iron, of composition equivalent to a hexa-hedrite. Two enclaves are revealed as: an atypical olivine-hypersthene chondrite (in the mode, the olivine is Fa19, and pigeonite takes the place of orthopyroxene, but the chemical analysis is typical except for a small but appreciable carbon content); and an enstatite chondrite displaying crudely formed chondrules (chemically typical, with a small but appreciable carbon content).

The chondrite enclaves are not recrystallized: though Lovering has referred to the first as ‘thermally metamorphosed’, and both are dark coloured, there seems to be little evidence of the effect of the metallic host, which must surely have been molten, on the chondrite enclaves, which seem to have been able to survive in this environment without mineralogical or textural modification.

Lovering has stressed the importance of this meteorite in its bearing on meteorite provenance and genesis, and the further implications of this present study are discussed briefly.