Two contrasting reaction coronae were developed around rare earth element (REE) accessory phosphates in Variscan metagranitic rocks, which have been overprinted by Alpine blastomylonitisation from the Fabova Hol'a Massif, in the Veporic Unit, Western Carpathians, Central Slovakia. The Th–U–Pb total EPMA age determination of primary magmatic monazite-(Ce) from the metagranite indicates a Carboniferous (Mississippian, Tournaisian) age of 355 ± 1.9 Ma. Monazite-(Ce) breakdown resulted in impressive, though common, fluorapatite ± Th-silicate + allanite-(Ce) + clinozoisite coronae. The alteration of xenotime-(Y) produced a novel type of secondary coronal micro-texture consisting of a massive fluorapatite mantle zone and tiny satellite crystals of hellandite-(Y) [(Ca,REE)4Y2Al□2(B4Si4O22)(OH)2] and hingganite-(Y) [Y2□Be2Si2O8(OH)2] of ~1–5 μm, and rarely ≤10 μm in size. The localised occurrence of Y–B–Be silicates, which are associated closely with other secondary minerals, suggests the involvement of B and Be during the metasomatic alteration transformation of xenotime-(Y). General reactions for monazite-(Ce) and xenotime-(Y) decomposition, including the fluids involved, can be written as follows: Mnz + (Ca, Fe, Si, Al and F)-rich fluid → FAp + Ht + Aln + Czo; Xtm + (Ca, Fe, Si, Al, F, B and Be)-rich fluid → FAp + Hld + Hin + Czo.

The granitic rocks underwent Early Cretaceous burial metamorphism under greenschist- to lower amphibolite-facies P–T conditions. Subsequently, Alpine post-collisional uplift and exhumation of the Veporic Unit, starting from the Late Cretaceous epoch, was accompanied by a retrograde tectono-metamorphic overprint; the activity of external fluids, caused the formation of secondary coronae minerals around monazite-(Ce) and xenotime-(Y). A portion of B (± Be) should have been liberated from the metagranite feldspars, micas, or xenotime-(Y) enriched in (Nb,Ta)BO4 (schiavinatoite or béhierite) components. However, the principal source of B and Be in fluids necessary for the production of hellandite and hingganite, was probably of external origin from adjacent magmatic, metamorphic, or sedimentary rocks (Permian granites, rhyolites and sedimentary rocks, and Palaeozoic metapelites).

Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system.

Sixteen samples of Middle and Upper Chalk from the Chilterns yielded what appear to be fragments of fish scales, spines, and bones, which consist of collophane. X-ray examination by the powder method shows that the material has an apatite-type structure with cell dimensions close to those previously reported for francolite. Examination of single grains shows that the optical anisotropy is due to preferred orientation of the c-axes of the crystallites and this direction corresponds to the faster vibration direction. Such grains are found to be pseudouniaxial negative. Preferred orientation could not be detected in isotropic grains.

The abundance of the well-known potassium aluminium silicate minerals, orthoclase, microcline, and muscovite, stands in striking contrast with the rarity of the little-known potassium aluminium phosphate minerals. The only one of these which occurs as distinct crystals and which has yielded a satisfactory formula is minyulite, KAl2(PO4)2(OH,F).4H2O. This mineral was first described by E. S. Simpson and LeMesurier from Western Australia in 1933 and an examination of well-crystallized specimens from South Australia by L. J. Spencer et alii was published in 1943. Spencer's paper included X-ray single-crystal and powder data for minyulite. X-ray, optical, and specific gravity data were also determined at that time for a few other hydrous potassium aluminium phosphate minerals from the British Museum collections. These included palmerite from guano deposits in a large cavern, Monte Alburno, near Controne in Salerno, Italy, presented by E. Casoria who described the mineral in 1904, and taranakite from the Sugarloaves, near New Plymouth, Taranaki, New Zealand.

Examination of previous physical methods of estimating the barium-content of these feldspars showed that they are generally unsatisfactory. A new variation diagram is constructed correlating BaO content and values of d132 determined from diffractometer records. It is estimated that the BaO content of these feldspars can normally be determined to about 2–3% by using this diagram.

Some of the problems of the mineralogy of the series are reviewed in the light of the experimental results, in particular the effect of polymorphic changes on the variation diagram. Some experimental evidence of the effect of different structural states upon the value of d132 is obtained, and the limitations imposed upon the method by the existence of such states are discussed.

A P21/c synthetic (Ca0.2Co0.8)CoSi2O6 pyroxene was synthesized by slow cooling from melt at high pressure. Single crystals suitable for X-ray diffraction were obtained and refined. The results were compared to those of C2/c pyroxenes along the series CaCoSi2O6–Co2Si2O6. Strong similarities in the crystal chemical mechanism of the transition with the synthetic CaFeSi2O6–Fe2Si2O6 and CaMgSi2O6–Mg2Si2O6 pyroxenes, both at an average and local level are apparent.

The results, examined together with two new refinements of pigeonite in the ureilites ALHA77257 and RKPA80239 and with a set of natural and synthetic C2/c and P21/c pyroxenes, show that the average cation radius in the M2 site is the driving force for the phase transition from C2/c to P21/c. The longest M2–O3 distances and the O3–O3–O3 angles follow the same trend, dictated only by the ionic radius in M2, in either synthetic or natural pyroxenes, regardless of the ionic radius of the M1 cations. The transition also affects the difference between bridging and non-bridging oxygen atoms and the extent of tetrahedral deformation, whereas the M1–O, M2–O1 and M2–O2 distances are unaffected by the transition and are determined only by the ionic radius of the bonding cation. The structural changes between the ionic radius and the high temperature C2/c and P21/c transitions are similar, and different to the high-pressure transition.

Analysis of natural and synthetic pyroxenes shows that the transition with composition occurs in strain free pyroxenes for a critical radius of 0.85 Å. Increasing strain stabilizes the P21/c structure to a higher temperature and larger cation radius.

Finally, our results show that the monoclinic P21/c Ca-poor clinopyroxene, i.e the mineral pigeonite, crystallizes only at conditions where the structure is HT-C2/c, and changes to the P21/c symmetry during cooling.

During the course of a study of the interaction of certain pure refractory oxides at high temperatures it became necessary to obtain accurate values for the lattice parameters of α-alumina and chromic oxide. Values obtained by previous workers, listed in table I, did not attain a greater accuracy than one part in 2000, whereas the use of large-diameter powder cameras calibrated with quartz now yield lattice parameters accurate to at least one part in 30,000.

Samples of the calcined oxides were examined in a 19 cm. diameter powder camera, alumina with cobalt Kα radiation and chromic oxide with chromium Kα radiation. Results are given in tables II and III.

This new mineral was first found by a miner named Cann in 1903 or 1904 on the 480-foot level of the Bultfontein mine at Kimberley. It occurred, associated with calcite, apophyllite, and natrolite, in a large ‘horse’ of dolerite and shale fragments enclosed in kimberlite. This huge inclusion, several hundred feet in height, undoubtedly formed part of the country-rock that now encloses the kimberlite pipe. The Specimens of the new mineral were considered to be natrolite and were presented to Mr. A. F. Williams. Several years later the same mineral was found by Mr. C. E. Adams in the Dutoitspan mine, which is located about half a mile from the Bultfontein mine; he presented his specimens to the MacGregor Museum at Kimberley. Recently, Mr. Miller, Underground Manager of the Jagersfontein mine in Orange River Colony, discovered the new mineral in that mine, which is located 100 miles south-east of Kimberley.

A thermogravimetric vacuum microbalance has been used to study the reaction between β-soluble anhydrite and water vapour in the temperature range 20–100° C. Equilibrium water-vapour pressures for the hydration reaction in this temperature range were determined directly and have been compared with available data obtained by Kelly, Southard, and Anderson (1941) in the temperature range 80–120° C. The kinetics of the hydration and dehydration reactions have also been studied in a series of isothermal experiments with varying water-vapour pressure. These experiments indicate that in a vapour-pressure range close to the equilibrium value very low rates for both hydration and dehydration are observed. Outside this range of vapour pressures both hydration and dehydration rates increase suddenly and show an approximately linear increase with imposed water-vapour pressure.

At low temperatures (25° C) the dehydration reaction has an associated activation energy of approximately 10 kcal mole−1. In the same temperature range additional, physical adsorption of water vapour by the specimen was noted.

The central region of a type 1 stone was found by optical and X-ray topographic examination to be densely populated with small inclusions. The X-ray studies indicated that these were precipitates formed after growth of the stone. Precipitate sizes fell into two groups, 1 µ or less, and around 5 µ. Many cases of decoration of grown-in dislocations by these precipitates were observed.

A new occurrence of the tantalum minerals simpsonite and stibiotantalite is described from a lithium pegmatite at Mtoko, Southern Rhodesia. Optical, chemical, and powder X-ray data are given and the formula of simpsonite is considered; a new formula is proposed.

In this paper is described a series of three small pcgmatite dikes and the skarns produced by them in Dalradiau ealc-silicate hornfelses, and after full discussion certain conclusions are deduced as to the mode of origin of these rocks. This suite has not been described previously and lies to the south of Bunbeg quay and to the east of Loughlin island (fig. 1). Tim only published accounts of the area contain but passing reference to some of the features here described. In 1891 Nolan (1) merely noted the existence of 'remarkable beds of garnetiferous limestone withtremolite' near the small village of Bunbeg, whilst Zealley (2) in 1909 briefly referred to these hornfelses.

Metamorphosed dyke rocks in Witwatersrand gold mines carry pyrite crystals of unusual appearance. These crystals, particularly along the dyke margins, show curved and scratched surfaces that cut across crystal faces. The abrasion of the crystals is due to movement of dyke material under pressure. There is some suggestion of surface flow on the abraded surfaces. No deformation or granulation was obtained in laboratory experiments on pyrite crystals. Pressure shadows around the pyrite are described.

In 1912 Mr. N. B. Kinnear, Curator of the Bombay Natural History Society's Museum, brought to me at the British Museum, for identification, a specimen of a supposed meteorite which had been sent to the Bombay Natural History Society by the late General W. Osborn.

General Osborn stated that, in November, 1910, on arrival at his usual winter quarters in the hill station of Kotheir in the Punjab, he visited his friend, the Rajah of Bilaspur, who presented him with a fragment, weighing about a quarter of a pound, of a meteorite which had fallen in daylight at the village of Baroti, in the Bilaspur (Simla) district, one day during the month of September, 1910.

In Moinian metasediments regionally metamorphosed to sillimanite grade, garnet has subsequently been re-equilibrated in the inner (cordierite-potash feldspar) zone of the aureole of the Strontian Granodiorite. Zoning profiles of garnet from the aureole, and from surrounding regional assemblages, show retrograde Mnrich rims. Some regional garnets are also internally zoned. In the aureole as a whole, the partition measure for Fe and Mg between garnet and biotite shows a correlation with that for Ca between garnet and plagioclase. If interpreted in terms of a simple equilibrium model, this might suggest that pressure decreased with increasing temperature towards the granodiorite, but the trend can more plausibly be attributed to deviation from ideal solid-solution behaviour of Ca in garnet and plagioclase, with incomplete homogenization of garnet as a complicating factor in the outer parts of the aureole. From the difference in the temperature thresholds for garnet core equilibration, the timescale t2 of the thermal event relative to the regional t1 is estimated as t2/t1 ≅ 10−1.1±0.7, consistent with emplacement of the intrusion at an early stage of regional cooling.

Examination of some pyroxenite nodules from the Jagersfontein kimberlite shows that they have suffered variable deformation followed by different degrees of recovery. Most interes~ting of the nodules is the 'diallage rock', which consists of highly sheared and broken lamellar crystals of diopside containing exsolved enstatite. Petrographic evidence indicates a pre-tectonic exsolution of enstatite and a syntectonic exsolution of pyrope-almandine from enstatite. Deformation occurred in the mantle, prior to incorporation of the nodule in the kimberlite. Compositions of pyroxenes from the diallage rock suggest it re-equilibrated at a temperature of 1000° and at a pressure of about 35 kb. Olivine and phlogopite, accompanied by serpentine, occur only in broken kink-bands in the diallage rock and they are considered to be of secondary origin, precipitated from kimberlite magma at temperatures near 700°

Ore microscope and electron microprobe investigations on Zn-Pb-Ag ores from B Zone in Silvermines, Ireland, have shown the presence of two As-Sb-Ag phases; a tetrahedrite-group mineral with composition Cu6.3Ag3.7Fe0.9Zn1.2As2.2Sb2.1S12.7 and proustite-pyrargyrite (Ag3As0.5Sb0.5S3). It is postulated that both phases inherited their As and Sb from primary geocronite (Pb14.5As3.4Sb2.6S23) and that they are metastable. An enrichment in Ni in the ores is due to very fine to submicroscopic intergrowths of gersdorffite (Ni0.6Fe0.4AsS) with geocronite and with galena.

Astrophyllite has been found in alkalic pegmatite dykes on the two sides of Kangerdlugssuaq fjord. At the eastern locality, Kraemers Island, the dyke is silica oversaturated and the astrophyllite occurs in a broad tabular crystal habit. The dyke at the western locality, Bagnaesset, is silica undersaturated and the astrophyllite occurs in elongated prisms of acicular habit. Electron probe analyses of the crystals of the two habits have shown systematic chemical differences which not only relate to Mn and Ti compositional variations, but also reveal departures from ideal stoichiometry in varying degrees. Based on this latter feature a model involving polysomatism has been constructed which may explain the differences in crystal habit.