The alkali feldspars in the Ardara pluton are microcline- and orthoclase-microperthites. Their compositions have been determined by the 20 X-ray method, both before and after homogenization. The bulk compositions are very rich in potassium as a result of postmagmatic recrystallization of the alkali feldspar. There is no significant variation in either the bulk composition or the composition of the potassic phase in different parts of the intrusion. The structural state of the feldspars has been studied by measurement of 2V and obliquity of the potassic phases, and the reciprocal lattice angles α* and γ* of the potassic and sodic phases in selected crystals. Most of the specimens contain near-maximum microcline, but there is a decrease in the obliquity of the potassic phase at the eastern end of the intrusion. This can be related to the subsequent intrusion of the Main Donegal Granite.

Zinckenite was first described in 1826 by G. Rose, who determined it to be an orthorhombic mineral. The crystals were thought to be seldom single, but to occur in nearly hexagonal forms as a result of twinning in some fashion similar to that found in aragonite. The presence of longitudinal striations on the lateral faces was taken as further evidence that the crystals were twinned. The composition was given by H. Rose as PbSb2S4 or PbS.Sb2S3. The original specimens which were described came from the antimony mine of Woffsberg in the Harz.

In 1922 S. G. Gordon described a new lead sulfantimonite from Oruro, Bolivia, which he named keeleyite. This mineral he presumed to he orthorhombic, although no measurable crystals were found, and the formula was given as Pb2Sb6S11 or 2PbS.3Sb2S3.

There occurs frequently in coal a white carbonate which, when it is referred to at all by scientific writers on coal, is usually described as calcium carbonate. It occurs as a rule in the form of thin layers infilling the joint-cracks which lie normal to the bedding-planes, though at times it may be seen infilling other divisional planes which may cut across the bedding obliquely.

Cristobalite is found as the first product in the conversion of quartz following a high-temperature heating, and it constitutes a large percentage of the crystalline material in most manufactured silica bricks. It is present also in fireclay products, the amount being dependent upon the nature of the raw material and the conditions of firing. In the majority of these products the cristobalite is only poorly developed, i.e. the crystals are only perfect over distances of the order of about 1 × 10-6 cm. This value is derived from the diffuseness of the high-order reflections on the X-ray powder photograph. On the other hand, the crystals of cristobalite are well developed in the hot face of an open hearth silica roof-brick.

The orientation of the boundaries of out-of-step domains in ‘transitional’ anorthite has been deduced from the direction of elongation of the diffuse X-ray reflections h + h + l = 2n + 1 in selected precession photographs. The reflections are elongated normal to which is in the zone and contains the body-centring vector (a+b−c)/2. The structure is presumed to be perfect parallel to . Atoms in essentially identical, primitive anorthite-like domains are related across the out-of-step domain boundaries by body-centring vectors. Increasing diffuseness of the h + k + l = 2n + 1 reflections indicates progressively smaller domains (more frequent domain boundaries), and when thesereflections disappear, the structure has become body-centred on the average.

Among the lead and zinc minerals which occur in the Rhodesian Broken Hill mine workings at what used to be No. 1 Kopje (now represented by a hole in the ground) copper compounds are occasionally to be seen. Their quantity is always very small, but they are readily noticeable on accouut of their colour. They include malachite, chessylite, cuprite, copper-glance, and undetermined phosphates, and, what is more, interesting, double salts of copper and zinc.

Some years ago a few small grains of an unknown mineral were separated by F. H. Stewart from well cuttings from the Permian lower evaporite bed of the Eskdale no. 2 borehole, sunk by the D'Arcy Exploration Company near Aislaby, north Yorkshire. The mineral (not then identified) was mentioned in an account of the mineralogy of this evaporite bed (Stewart, 1949, p. 626). Flame tests suggested that boron and strontium were present, and this was confirmed by Dr. R. L. Mitchell of the Macaulay Institute for Soil Research in Aberdeen, who, by spectrographic work, found that these were the main constituents, and that very much smaller quantities of Ca, Mg, Ba, Na, and K were present.

Early this year Mr. Arthur Russell brought me a small specimen of ore from Mill Close mine, Wensley, Derbyshire, for identification. An X-ray powder photograph p1. xxviii, fig. 3, showed that the mineral has the pyrite structure with unit-cell edge a 5.49 Å., and a chemical analysis of a small sample of specific gravity 4·82, yielded Ni 16·69, Fe 29·30, S 53.40% (see table 1). These data identified the specimen as bravoite, a rare mineral new to the British Isles. At a later date Professor W. G. Fearnsides interested himself in our preliminary work and kindly provided me with further specimens of bravoite and accessory minerals from the Mill Close mine. These also have been investigated.

Sixteen samples of crocidolite asbestos from weathered zones in mines in Cape Province, Transvaal, Western Australia, and Bolivia have been studied by thermal analysis methods and their characteristics are compared with those of fresh crocidolite from Koegas-Westerberg given by Hodgson, Freeman, and Taylor (1965). New chemical analyses of these samples are reported.

The effect of natural weathering on crocidolite tends to a removal of ¼ of the OH groups and an adjustment of the Fe2+/Fe3+ ratio to unity, but there are only minor changes in the physical characteristics of the fibre. The d.t.a. pattern of decomposition is not affected by weathering, but the endothermic peak corresponding to final decomposition is moved to higher temperatures as the Mg content of crocidolite increases. Mg-blocking of this decomposition is considered to be more important than Mg-blocking of the oxidation reaction at 400–450° C, suggested by Addison et al. (1962).

D.t.a. and other evidence shows that the Transvaal crocidolite contains intergrown amosite fibres, and suggests that the Bolivian crocidolite is admixed with anthophyllite.

In this paper are embodied the results of an examination of the specimens of lead slags from Laurium in the British Museum. On some of the specimens a new mineral, paralaurionite, was found, which possesses the same chemical composition as laurionite, but entirely different morphological and optical characters.

In addition to crystals of the four minerals given in the title, a few crystals oi matloekite and anglesite were noticed, and on one specimen there is a radiating group of prismatic crystals of penfieldite.

In a general account of the properties of torbernite given by the present author in this magazine in 1916 it was shown that the transition from torbernite to the first dehydrationproduct, known as meta-torbernite I (meta-kupferuranit), was dependent on the temperature and the vapour-pressure, and that the boundary, of the stability area lay only a little outside the range of ordinary atmospheric conditions; the transition-point of torbernite in contact With water was determined as 75° C.

Two compounds, one an apatite and the other a perovskite, have been synthesized by sintering mixtures containing CaO and Cr2O3, and CaO, Cr2O3, and Fe2O3 respectively. The apatite formed by partial oxidation of the Cr2O3 and subsequent pick-up of moisture from the atmosphere, to give Ca5(CrO4)3OH. The perov-skite formed as a non-stoicheiometric compound Ca4(Fe,Cr)4O11 by partial oxidation of the Cr2O3 during firing. Lattice parameters and interplanar spacings are given for the two structures.

This is a mere fragment of gneissic rocks which is imbedded between the granite of Roeness and the igneous rock which lies to the east : but so different are these entrapped rocks from the ordinary gneiss of Shetland, and so violent a twist do they seem to have received athwart of their normal strike, that the enquiry rises-whence did this fragment come ?

A spectator looking west from the top of Ornsfield, gazes seaward upon a mere heap of ruins ; while, looking landward, he also sees little else,-so riven and twisted are the rocks by the intrusion of dykes of porphyry, and so shattered and toppling from the invasion of the sea.

Early in 1947 an unusual mineral deposit was discovered at Mavuzi in the Tete district of Mozambique. The discovery was made by native boys searching for corundum on behalf of Senhor Mario Canuto de Carvalho, a Goanese prospector who had for some years been associated with primitive gold and corundum operations on the north bank of the Zambesi. The dominant ore-mineral in the new deposit was superficially similar to the pegmatitic samarskite found in small quantities in the mica-mining districts of the Alto Ligonha in eastern Mozambique; and when exposure of the mineral to a photographic plate confirmed that it was radioactive, the identification as samarskite was accepted both by local prospectors and by most of the field geologists who later worked on the deposits. The presence of uranium in the ore was first proven in a chemical analysis by the Southern Rhodesian Geological Survey.

Within amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.

Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.

Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.

The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.

In that part of the Gangpur State immediately to the north of the Bengal-Nagpur Railway, between Biara and Garpos, lies a tract of dolomite- and limestone-bearing country which has been referred, on lithological grounds, to the Cuddapah (? Algoukian or Palaeozoic) formation. From this area, all the dolomite and most of the limestone requirements of the Bengal iron and steel industry are at present derived, and the close proximity of the enormous haematite ore reserves of Singhbhum indicates a still greater economic importance for these materials in the future.

Apreliminary account of this fine mass, weighing 2520 lb., of meteoric iron was given in 1910 by L. Laybourne Smith, who at that time was Registrar of the South Australian School of Mines and Industries in Adelaide; but the promised detailed description with chemical analysis never appeared. Except for a small piece cut off one corner (upper left-hand corner in fig. 1) the mass is preserved intact in the Museum of that Institution, and none of the material appears to have been distributed to other museums. Casts of the mass were, however, made for the South Australian Museum in Adelaide, and one of them was presented to the British Museum in 1917 (B.M. 1917,360), where in the meteorite collection it is a very striking object (fig. 1).

Recently, at the suggestion of Mr. R. Bedford of the Kyancutta Museum, the Council of the South Australian School of Mines has generously presented to the British Museum a piece of this meteoric iron, together with the milling cuttings, with the request that the description of it should be completed.

Thermal behaviour of fibrous tremolite from Maryland, USA has been investigated in situ up to breakdown temperature. Tremolite can be found both as primary constituent and as contaminant in Asbestos Containing Materials (ACMs). The products of breakdown are subcalcic diopside and calcium-rich clinoenstatite in a 2:1 ratio, traces of hematite plus minor silica-rich amorphous material. Thermal expansion follows a regular trend up to 723 K before the onset of Fe2+ oxidation/OH– deprotonation which is completed at 1023 K. At 923 K the Fe3+ migration starts towards M(1) and the corresponding counter-migration of Mg to M(2) and M(3). At T close to structure breakdown, M(2) shows a significant site-scattering reduction possibly consistent with the occurrence of minor vacancies. In fully oxidised tremolite, Fe3+ is allocated prevalently at M(1) and subordinately at M(3). As it is well-known that M(1), along with M(2), is the most exposed octahedral site at the surface of amphiboles, most of the Fe3+ is available for participating in the Fenton-like reactivity of oxidised tremolite, potentially making it dangerous for human health. This point should be properly taken into account in the evaluation of the safety of thermally decomposed tremolite-containing ACMs, in particular in the case of accidentally incomplete treatments.