Rapid, accurate silica determinations have been made titrimetrically following decomposition by HClO4-HF in a ‘Teflon’ vessel, the volatilized silicon tetrafluoride being precipitated as K2SiF6 in a HF-KF-glycerol-alcohol mixture. After filtration and washing with alcohol the precipitate is dissolved in boiling water, then titrated with NaOH. This method has many advantages over conventional gravimetric or spectrophotometric procedures.

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.

Chemical analyses, optical properties, and specific gravities are presented for nine axinites. A reciprocal substitution relationship is demonstrated between Mg and Mn2+, and a linear variation diagram is constructed between refractive indices and the (Fe2++Fe3++Mn2++Ti) ions calculated on the basis of 16(O,OH). The composition of these axinites is independent of the composition of their host rocks; their colour appears to be independent of the Fe2+/Mn2+ ratio for the range of iron and manganese values of the specimens investigated.

Troilite is a sulfide that occurs commonly in meteorites. In the laboratory, it can be synthesized by gas-solid reaction of metallic Fe and H2S-H2 gas mixtures. In this research, the arc-discharge method was used to synthesize troilite. The resulting spherules are up to 2–3 mm in diameter and composed of troilite, pyrrhotite and metallic Fe. Nanometer-sized hollow carbon fibres and balls occur on the surface of the spherules. The features and coexisting relationships of the constituents of the spherules were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the phenomenon of transformation of pyrite (FeS2) into pyrrhotite (Fe1-xS), troilite (FeS) and metallic Fe under arc-discharge reducing conditions were examined.

In October 1875 the late J. G. Goodchild recorded his then recent discovery of a mineral which he stated 'he believed' to be wulfenite and which he had found on an old mine dump near Carrock Fell, Troutbeck, Cumberland. One specimen only was, I believe, found by Mr. Goodehild, and this he presented to the Carlisle Museum, where it has been seen by myself, the label bearing the more precise locality of Brandy Gill.

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 this paper an attempt is made to state and explain, in a simple manner, the essential features of the phenomena which are seen when plates of pleochroie minerals are examined in ordinary light.

The pleochroie effects exhibited by minerals are usually studied in light of practically normal incidence. For the observation of facial colours, transparent crystals, or, better still, specially orientated cube-shaped pieces of minerals, are examined in ordinary light. In general, by this mode of observation, only facial colours are seen when ordinary light is used, and for the observation of axial colours the incident light must be polarized.

Lengenbachite is one of the interesting minerals which occur in the dolomite of the Binnenthal, and we owe our knowledge of it, as of many other new species, to the careful investigations conducted in recent years by Mr. R. H. Solly at that remarkable locality. The crystallographic and physical characters, so far as they have proved capable of determination, have been already described by Mr. Solly in the pages of this Magazine (vol. xiv, p. 78). The material which he kindly placed in my hands for chemical examination consisted of cleavage-plates, exhibiting brilliant metallic lustre, and of foliated aggregates of thin greyish-black crystals. Some of the crystals were partially covered with a thin, white incrustation readily removed by boiling dilute hydrochloric acid, a reagent which appeared to be without action on the lengenbachite.

Rhombohedral (3R) molybdenite has hitherto been reported from only one locality. Its mode of occurrence at a new locality is reported in this paper. At Panasqueira it occurs as a rare accessory in greisenized granite with which wolframite-cassiterite-quartz veins are associated. In the veins themselves only normal hexagonal (2H) molybdenite has been detected.

Zoning in plagioclase is reported from the charnockitic rocks of Kondapalli, Krishna district, Andhra Pradesh, India, for the first time. Electronprobe studies indicate that the zoned plagioclases consist of homogeneous sodic cores mantled by thin calcic shells, which show continuous zoning of the inverse type. Partial chemical analyses of twelve density fractions of the zoned plagioclase from a basic charnockite exhibit a wide variation in An content from 54·80 to 72·39 %; X-ray studies suggest that they possess ‘fixed’ transitional structural state.