This study presents the first crystal-structure determination of natural MgCO3·5H2O, mineral lansfordite, in comparison with previous structural works performed on synthetic analogues. A new prototype single-crystal X-ray diffractometer allowed us to measure an extremely small crystal (i.e. 0.020 mm × 0.010 mm × 0.005 mm) and refine anisotropically all non-hydrogen atoms in the structure and provide a robust hydrogen-bond arrangement. Our new data confirm that natural lansfordite can be stable for several months at room temperature, in contrast with previous works, which reported that such a mineral could be stable only below 10°C.

Chromite occurs together with olivine as phenocrysts in basalts of the Kanakasu greenstone body. Chromite forms inclusions within olivine phenocrysts; it also constitutes discrete phenocrystic grains scattered in the groundmass. The Cr and Ni contents of chromite-bearing olivine basalts are unusually high relative to the MgO content. This is probably due to the presence of phenocrystic chromite and olivine. The mineralogy suggests that the groundmass of the basalts is hawaiitic in composition. Chromite, generally, is unlikely to crystallize from differentiated magma such as hawaiite melt. The chromite and associated olivine phenocrysts are probably xenocrysts. Discrete chromite commonly shows compositional zoning that resulted from reaction with host magma; some chromite evidently changed in composition. Chromite embedded in olivine was shielded from reaction with host magma, and has preserved the original chemical composition. The composition of embedded chromite ranges: Mg/(Mg+Fe2+) 0.37–0.58, Cr/(Cr+Al) 0.47–0.64, Fe3+ 0.16–0.47 p.f.u., and Ti 0.034–0.13 p.f.u. The relatively high Ti and Al contents suggest that chromite crystallized from an alkalic basalt magma. The Cr/(Cr+Al) ratio is relatively high when compared to those of chromite in mid-oceanic ridge and island-arc alkalic basalts; the Kanakasu embedded chromite is chemically identical to chromite from Hawaiian alkalic basalts. The Kanakasu chromite was probably formed in an intraplate oceanic island.

Six natural crystals from the Sludyanka crystalline complex belonging to the eskolaite (Cr2O3)–karelianite (V2O3)–hematite (Fe2O3) solid solution were studied by means of X-ray diffraction and electron microprobe. The Fe3+-poor samples show a general increase in a and c cell parameters with increasing mean cationic radius (MCR), consistent with that shown by the synthetic crystals along the eskolaite–karelianite join. The Fe3+-richer sample deviates significantly from the behaviour shown by the Fe3+-poor ones, similar to synthetic and natural hematites; with increasing MCR, the a and c cell parameters increase linearly along the eskolaite-karelianite join. However, for the samples rich in Fe3+, from karelianite to hematite, a shows a slightly steeper slope whereas the c parameter decreases strongly. The octahedral distortion increases slightly as a function of MCR along the eskolaite-karelianite join, whereas it increases markedly for Fe3+-rich samples. The evolution of the octahedral edges and of the octahedral distortions as a function of MCR are responsible for the behaviour of the unit-cell parameters along the eskolaite-karelianite-hematite join.

A re-examination of the mineral scolecite has shown that the previously published monoclinic (pseudo-orthorhombic) unit cell is face-centred and that the Hermann-Mauguin spacegroup symbol has been incorrectly assigned. The reduced monoclinic cell yields a 9·85 Å, b 18·98 Å, c 6·52 Å, β 110° 61; space group Aa. New indexed powder data are included.

Radial and longitudinal temperature gradients within cold-seal pressure vessels can contribute significantly to the total temperature unccrtainty in any one experiment and it is important to calibrate such gradients before experiments are undertaken. We have measured temperature gradients in vertically mounted large cold-seal vessels at 1 atm and 1 kbar and in the temperature range 500–800°C Radial gradients were measured with the vessel at various positions within the furnace by recording the temperature difference between a thermocouple in the internal bore of the vessel and one in a well in the top of the vessel. We find that when the vessel is at a certain position in the furnace, the temperatures read by these two thermocouples are equivalent to within 1°C. The contribution of radial gradients to temperature uncertainty can be thus be substantially minimized if experiments are undertaken with the vessel in this position. Longitudinal gradients of 2.8°C/cm at 500°C and 3°C/cm at 800°C were recorded at 1 kbar. These profiles are significantly steeper than those recorded at 1 atm. Not to calibrate temperature gradients at the experimental conditions or failure to calibrate vessels at all could lead to large temperature uncertainties.

For several years now it. has been generally appreciated that plagioclase felspar formed at high temperature differs optically from that formed at lower temperatures. Much of the evidence for this has been provided by the Austrian workers, notably Köhler (1-3), Scholler (4), and Tertsch (5-7), who have prepared revised curves to supplement the universal-stage stereograms of Reichert (which are for use with lowtemperature material). There are a number of interesting petrological points which have not yet been fully investigated. Much work has been done on synthetic material, and it is not clear to what extent the hightemperature forms occur naturally. There may be two distinct and separate types of plagioclase structure, or the two forms may grade into one another. It may be possible to explain the optical anomalies as an order-disorder phenomenon; a more disordered state has been 'frozenin' in those felspars which ha~e formed a.t a high temperature and cooled rapidly.

The Middle Lias of Rutland, east Leicestershire, and north-west Northamptonshire was described by Judd in 1875 as comprisingan upper ferruginous member—-the Marlstone Rock Bed-—and a lowerargillaceous division of blue clays, often micaceous or sandy, and carryingbands of 'septaria' and of 'ironstone balls'. In the septaria he recordedthe occurrence of 'specular-iron, zinc-blende and pyrites'.

During the six-inch survey of one-inch New Series sheets 157 (Stam-ford) and 171 (Kettering) together with the adjacent parts of sheets 156(Leicester) and 170 (Market Harborough) a considerable area of thelower argillaceous division was mapped.

From a metallographic study the thermo-mechanical history of Kodaikanal is proposed as a slow structure-forming cool, followed by mechanical damage, then mild reheating, and finally entry to earth.

The determination of the specific gravity of a solid which is only available in small quantity has always been a difficult problem in cases where the suspension method fails, either because the solid is too dense, or because it dissolves in or reacts with the heavy liquids available. It is hoped that the following method will be found a useful addition to the numerous methods which have been proposed from time to time to meet such cases. References to most of these methods are given at the end of the paper. Neither the new method nor any one of the older ones is universally applicable, and the best method for any particular case will depend on many circumstances.

The fluorites of the Transvaal occur in different rock-types, viz in the dolomite of the Transvaal System, in acidic rocks (red granite and granophyre of the Bushveld igneous complex and Rooiberg felsites), and in alkalic rocks. The purpose of this study was to determine:

1. (1) What minor elements are present in selected fluorites.

2. (2) What the effect of these elements is on the respective cube-edges.

3. (3) Whether these elements have any geological significance.

Fluorite displays a wide range of colour; both colourless and distinctly coloured specimens were examined. Differently coloured varieties could in some instances be taken from the same sample. The choice of coloured varieties in the different rock-types was nevertheless limited. Only light-coloured fluorites occur in the dolomite, whereas the alkalic rocks yielded only very dark purple specimens.

The third occurrence of stokesite was discovered in a desilicated pegmatite at Věžná, Western Moravia. In this locality, stokesite accompanies columbite, cassiterite, and stibian pyrochlore-microlite, in a miarolitic cavity of albite. The X-ray data and the optical properties of the Věžná stokesite agree well with those observed by previous authors.

Thomas Pennant was born at Downing, Whitford, near Holywell, in 1726. A contemporary and correspondent of Linnaeus and Buffon, he is well known to zoologists as a pioneer of British zoology, and to him were addressed the letters of Gilbert White which form the greater part of 'The Natural History and Antiquities of Selborne'. He travelled very extensively in the British Isles and wrote many accounts of his tours, perhaps the best known being his account of London and his 'Tour in Wales'.

Mapping of the distribution of zeolites in the Antrinl basalku has revealed that gmelinite is confined to a narrow zone along the eastern seaboard of Antrim. This zone comprises less than 1% of the area of the basalts, but in it gmelinite is extremely abundant. The gmelinite zone is superimposed upon the lava pile, and the minerals in it are clearly later than the laves; it is in the form of a dome, elongated north-west and traceable for 18 or 24 miles in this direction, and is found in the basal parts of the lava pile, locally reaching a height of some 500 feet in the pile. The zone may be related in its position and origin to the Island-magee fault zone. Gmelinite frequently forms a parallel overgrowth on chabazite. Superimposed upon the southern part of the gmclinite zone is a zone of late chabazite and heulandite containing, inter alia, parallel overgrowths of late chabazite on simple or twinned gmelinite.

Trace element variations in stream sediments from an area of 76 000 km2 in central Colorado are used to identify uraniferous granitoids on the basis of whole rock geochemical criteria developed to distinguish barren from metalliferous granitoids in Britain. These criteria (which include enhanced Ba, Be, Cs, Cs/Ba, K, La/Eu, Li, Lu/Eu, Nb, Rb, Rb/K, low Sr and Mg, and RE patterns with marked negative Eu anomalies) are used to formulate an index based on the Pikes Peak batholith of the Front Range as a type uranium source rock.

Uraniferous granitoids in Colorado, which are associated with sedimentary basins containing major uranium mineralization, are identified using this index which may be applicable to the interpretation of stream sediments from elsewhere. The use of stream sediment geochemistry as an exploration method for similar uranium source rocks, which may indicate potential uranium provinces, is thus possible.