The relationships between the 2:1 layer silicates are discussed in terms of the charge balance between the ions occupying X, Y, and Z sites. This brings out the relationship of glauconite to the illites, and clarifies the reason for the ideal occupancy of the Y sites in montmorillonite. It not only shows hectorite, saponite, and sauconite to be tri-octahedral smectites, but also shows vermiculite to be a tri-octahedral analogue of the illites. Apparently anomalous differences in permitted compositions of the di-octahedral and tri-octahedral micas are explained in terms of mismatch between the tetrahedral and octahedral layers, and it is shown that ephesite is to be regarded as a tri-octahedral common mica, not an analogue of margarite. Anandite is the nearest known naturally occurring equivalent to a tri-octahedral analogue of margarite, but the true analogue is a barium magnesium mica synthesized by Frondel and Ito.

The meteorite was an oriented polyhedron, which broke up into at least two parts after entry into the Earth's atmosphere. It has undergone some degree of terrestrial weathering. A cut surface of the meteorite shows light-grey interior with sporadic rusty-brown patches and a distinct brown alteration zone close to the fusion crust. Weathering has resulted in preferential replacement of NiFe by limonite, and veining of minerals by goethite.

Rewari is an equilibrated chondrite with rare ghosts of chondrules and at least one lithic fragment. Composition of olivine, as indicated by microprobe analysis is Fa23, which agrees well with bulk wet chemical analysis; that indicated by d130 is Fa18–20. From the outer surface inwards, four petrographic zones can be distinguished in the meteorite: a skin, about 0.01 mm thick, a troilite-poor zone slightly thicker than the skin, a troilite-rich ‘soaking zone’, about 0.5–0.6 mm thick, and a relatively coarse-grained interior. These are described in detail.

The interior of the meteorite is composed of relatively coarse-grained crystalline silicates with disseminated metallic minerals including plessitic and zoned inter-growths of kamacite and taenite. The matrix shows a high degree of integration with the chondrules. The coarse texture and zonation of taenite may be the result of protracted heat treatment responsible for recrystallization. The constituent grains show considerable shock effects such as fracturing, comminution, veins of shock-melted pseudotachylite, pressure twinning, and undulose extinction. Chemical composition (mean of two wet chemical analysis) of the meteorite is: metallic Fe 7.475, Ni 0.975, Co 0.045; as sulphide Fe 3.200, Ni 0.090, Co < 0.01; SiO2 38.060, TiO2 0.10, Al2O3 2.34, Fe2O3 0.175, Cr2O3 0.485, FeO 13.950, MnO 0.210, NiO trace, CaO 1.875, MgO 26.265, Na2O 0.89, K2O 0.115, P2O5 0.285, H2O− 0.295, H2O+ 0.81, CO2 trace, S (total) 1.890, C (total) 0.19 per cent. The chemistry, mineralogy, and texture show that the Rewari meteorite is an L6 chondrite. Compared to average L-group chondrite it has a higher content of MgO and lower of SiO2, a little lower oxidation state, and tends to be enriched in siderophilic elements.

While undergoing 'dry' homogenization at 980°C the 2̄01 X-ray reflections of sodic lowalbite- microcline microperthites show that phase compositions recapitulate (but in a reverse timesense) the unmixing history of ordered feldspars about a solvus with a critical composition near 26 mole per cent KAlSi3O8.

The wittichenite (BM 1977, 172) discovered in the course of a reflected light study of polished sections from the Seathwaite deposit, Cumbria (described earlier in this journal by Stanley and Criddle), is the first authenticated occurrence of the species in Great Britain; for this reason it was examined in detail and compared with a specimen (BM 1437) from Wittichen, the type locality. Chemical analyses, cell dimensions, visible-spectrum reflectances, quantitative colour values, and VHN's are provided. They are in agreement with previously published data for the species.

The crystalline form of orpiment was first determined by Mohs (Grundriss der Mineralogie (1824), 2, 613).

His measurements, which he is careful to state were only approximate, gave an angle of 79°20' for the prism, and 83°7' for the brachydome; the plane of perfect cleavage being taken as the macropinakoid, and the crystals being referred to the orthorhombic system.

Two new finds of stony meteorites north-west of Kalgoorlie are described, and the masses covered by brief petrographic descriptions.

Conclusions concerning the unit-cell contents and chemical formula of a mineral are all too often drawn from a small part of the available data. A procedure is outlined by which any chemical analysis for which a density is available can be utilized, provided X-ray data are available for a reasonable range of analysed specimens. The effects of possible errors in the determination of water, and in the assessment of essential and non-exsential water, are discussed both qualitatively and quantitatively.

A survey of all available data for anthophyllite has not disclosed any specimens in which the number of oxygen atoms per unit cell is significantly in excess of 96 with the possible exception of the Glen Urquhart gedrite and the Edwards (New York) material. But it is certain that the number of cations per unit cell is normally well in excess of 60 (partial occupation of the A lattice positions), and that, although ‘excess’ water in sonic fibrous anthophyllites may be adsorbed impurity, the number of hydroxyl groups in others is well in excess of 8 per unit cell; it is also fairly clear that the number of hydroxyl groups may fall below 8 per unit cell.

In working on the isomorphism of Tourmaline I have been struck by the very peculiar development of a fine crystal from Pierrepont, New York, now in the Cambridge Collection.

The crystal is doubly terminated, of a jet-black colour and splendid lustre. It weighs 814.88 grammes, and measures 1⅙ inch by 1 inch by ½ inch.

In my address at the Annual Meeting of the Mineralogical Society last year, in Plymouth, I gave an account of a new method of studying the optical properties of minerals, and of determining their indices of refraction. I then showed that an approximate knowledge of these characters would, in many cases, enable us to identify minerals with great confidence, and also would sometimes furnish us with valuable hints as to their general chemical composition. My remarks had reference exclusively to detached specimens of more or less considerable thickness, and I scarcely thought that it would ever be possible to apply this method successfully with comparatively high powers in the case of thin sections of rocks. I feared that certain errors, which appeared to be unavoidable, would then become so great in proportion to the difference in the indices of many of the commoner minerals, that it would be impossible to distinguish them with confidence.

In order to determine the links between geochemical parameters controlling the formation of silica sinter in hot springs and their associated microbial diversity, a detailed characterisation of the waters and of in situ-grown silica sinters was combined with molecular phylogenetic analyses of the bacterial communities in Icelandic geothermal environments. At all but one site, the microorganisms clearly affected, and in part controlled, the formation of the macroscopic textures and structures of silica sinter edifices. In addition, the class and genera level phylogenetic diversity and distribution appeared to be closely linked to variations in temperature, salinity and pH regimes.

The availability of analytical methods that utilize the very intense and bright X-rays from synchrotron radiation sources has fundamentally changed the way in which geoscientists, environmental scientists and soil scientists study complex environmental samples and decipher the chemical and biological processes that impact the speciation, transport and potential bioavailability of environmental toxins (Brown et al., 2006). Such samples are often mixtures of crystalline and amorphous phases in particle-sizes ranging from cm to nm, adsorbed metal ions and organic molecules, natural organic matter, microbial organisms, algae, plant materials and aqueous solutions. The processes that affect the chemical forms and environmental fate of contaminants in such mixtures range from surface adsorption, desorption, precipitation and dissolution reactions, often involving a combination of hydrolysis, ligand exchange and electron transfer, to biological interactions in which microbial organisms, algae or plants interact with mineral surfaces and environmental contaminants.

In the early part of this year Mr. W Goodlet, laboratory assistant to Prof. Black, of the Dunedin University, submitted to me for examination a mineral specimen which he had brought from a journey of inspection of the gold fields of the West Coast, Middle Island. It had, so he told me, been broken from a boulder, about 40 lbs. in weight, which was found in the gold drift of a claim at Back Creek near Rimu, Westland, and placed aside by the claim owners as something uncommon, because of its weight and colour.

Stephanite has been the subject of two important memoirs. Schröder examined minutely the crystals from Andreasbcrg ; Vrba has described fully the character of the stephanite from Przibram and other localities, and has given at the same time a summary of the observations of previous mineralogists, so that his memoir constitutes a monograph of the mineral.

By neither of these observers, however, nor elsewhere, has it been stated that stephanite is hemimorphic, although it has been suspected of being possibly hemihedral.

It is the object of the present paper to establish the hemimorphism of stephanite upon evidence similar to that which has been employed in the case of pyrargyrite.

During the year 1919 specimens of some of the meteorites preserved in the Public Museum of King Willlam's Town, South Africa, were kindly placed by the Curator, the late Yr. F. A. O. Pyre, at the disposal of the writer for investigation. One of these specimens was a meteoric iron labelled Mount Ayliff, another a mass of oxidized material labelled Western Cape Province, and a third a small piece of iron labelled ‘found on Elandsburg at an altitude of 6,000 ft. in 1888’ Unfortunately Mr. Pyre was not in a position to supply very much more information about the specimens.