Euhedra of weddellite have been recognized in modern, unconsolidated sediments collected from depths of water not exceeding one fathom, along the south-east coast of Florida. For weddellite, the following data have been determined: crystals simple with r {011} accompanied by a {010} in some cases; goniometric axial ratio is a:c = 1:0·593 (meas.), 1:0·5938 (calc.); a0 12·360 Å, c0 = 7·340 Å; space group I4/m, I4 or I4̅; α 1·529, γ = 1·544, δ = 0·015, uniaxial, positive; d22°C = 1·941. Heat treatment of weddellite led to development of whewellite, calcite, and calcium oxide in turn as higher temperatures were employed; fully indexed X-ray diffraction powder data are given for weddellite, in addition to d-spacings and intensities for whewellite.

It is suggested that weddellite developed in the calcareous Florida sediments under conditions of storage over a two-year period, and ahnost certainly was not a constituent of those sediments at the time of collection. This raises the question whether weddellite was present in the Weddell Sea material at the actual time they were recovered by members of the Scotia Expedition.

It is suggested that the name shoshonite be revived for a group of potash-rich basalts and that the magma from which monzonites, potash-rich syenites, many lamprophyres, nepheline monzonites, shonkinites, eovites, ijolites, leucite basalts, leucitophyres, etc., have crystallized be called the shoshonite magma-type. This series shows parallels with the alkali basalt magma series, and the question of the relation of the two magma-types is discussed.

The name latite is discussed and rejected as a name for this potash-rich magma type. It is further shown that rocks of this composition invade geosynelinal regions that have been recently stabilized, one group of shoshonites being associated with an environment that is still subjected to minor folding and showing some relation to the cale-alkaline rocks, the other a true alkaline suite associated with non-orogenic conditions.

A modification of the rules for the cMeulation of C.I.P.W. norms when no normative quartz is present is suggested.

Present-day facies schemes are reviewed in relation to their definitions and applicability: a simplification is proposed based on assemblages in basaltic rocks, with secondary facies defined subsequently on pelitic assemblages.

Amongst the layered basic rocks of the Carlingford complex, is a gabbro which has been contaminated by a limited amount of Carboniferous Limestone. The clinopyroxene (Ca49Mg33Fe18) produced in the gabbro is similar to that found in teschenitic gabbros. Such features as the instability of olivine distinguish this contaminated tholeiitic gabbro from true alkaline types. The production of aluminous augite is discussed, and comparison is made with the basic rocks of Scawt Hill and Gunnedah. Analyses of the contaminated gabbro and contained pyroxene are given.

The petrography and mineralogy of a series of gabbroic xenoliths, consisting essentially of varying proportions of olivine, clinopyroxene, orthopyroxene, and plagioclase, are described from Gough Island. These are compared with xenoliths from other oceanic localities. Four new analyses of xenoliths and six of pyroxenes are presented, together with some partial analyses of plagioclases. It is concluded that the xenoliths are derived from the mantle above the magma source area. The composition of the mantle in this region is thought to be that of an olivine-tholeiite.

The cathodo-luminescence of minerals in thin sections of rocks has been examined with the aid of an electron-probe microanalyser and also with a simple electron source producing an unfocused beam. Experimental details of the technique are briefly described and colour photographs, taken at a primary magnification of 30 times, are included. The observed variations in colour and intensity of luminescence are interpreted in the light of electron-probe and spectrochemical determinations of trace elements. Applications of the technique are discussed.

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.

A new occurrence of kornerupine in the skarn zone at Mautia Hill, Tanganyika, has yielded unit-cell dimensions a 16·100, b 13·767, c 6·735 Å, density 3·297, and composition Na0·01Mn0·01Ti0·02Mg3·69Fe0·37IIIAl6·36Si3·71B0·41O21·75(OH)0·25. The unit-cell clearly contains 88 anions rather than the 86 proposed previously. Grandidierite from Sakatelo, Madagascar, has unit-cell dimensions a 10·978, b 10·335, c 5·760 Å, space group Pna21 or Pnam, density 2·976, and composition Fe0·12IITi0·01Mg0·88Fe0·03IIIAl3·00Si1·00B0·97O9·00. The unit-cell contains 36 anions and the structure appears to involve A106 chains parallel to the c-axis.

A preliminary account is given of an optical and electron-microprobe investigation into the pyroxene relations of Hawaiian hypersthene-bearing lavas. It is shown that the clinopyroxene jackets to the phenocryst hypersthenes consist of strongly zoned augite, not pigeonite as formerly believed; the compositional range of this pyroxene is approximately the same as that of the groundmass augite phase. Groundmass pyroxene relations are complex; in one case two distinct pyroxene phases, augite and pigeonite occur, in the other all compositions lying between augite and pigeonite are encountered.

Barringtonite, a new hydrous magnesium carbonate of composition MgCO3,2H2O, is recorded from Sempill Creek, Barrington Tops, New South Wales, where it occurs as nodular encrustations on the surface of olivine basalt. The mineral is triclinic, biaxial positive, has refractive indices α = 1·458, β = 1·473, γ = 1·501, 2Vγ = 73° 44′, and using Ito's method (1949) cell dimensions α = 9·155 Å, b = 6·202 Å, c = 6·092Å, α = 94· 00′, β = 95· 32′, and γ = 108° 72′. The three strongest lines on an X-ray powder photograph give d values of 8·682, 3·093, and 2·936 Å.

Basalts dredged from the floor of the deep ocean show general tholeiitic affinities. Some samples are rich in aluminium and of very similar composition to the Warner high-alumina basalt from California. Both olivine tholeiite and high-alumina basalt have been found in the form of glass in dredgings from the Mid-Atlantic Ridge, indicating that liquid magmas of both compositions have been erupted on to the sea bed in this area. In explanation of this association a tentative hypothesis of fractional melting of hydrated upper mantle material is proposed. It is suggested that under the mid-ocean ridges the ‘basaltic fraction’ of the mantle is locally in the form of an amphibole. Fractional incongruent melting of this amphibole appears to be a possible explanation of the range of composition encountered in dredged glass samples.

An account is given of the mineralogy and chemistry of the ‘pseudodiorites’ of Dielette, the hornfelses from which they are derived, and the contaminated granite veins associated with them.

Non-coaxial quartz- and mic-girdles in lineated quartzites from the Broken Hill District, New South Wales, are described and discussed.

The coarse-grained wolgidite variety of lamproite from the Wolgidee Hills of the West Kimberley District of Western Australia has previously yielded three new minerals. Two of these, wadeite and magnophorite (Prider, 1939), were discovered and described by the author when working as a research student under Professor Tilley's supervision and the third, priderite (Norrish, 1951), resulted from an X-ray study of material previously considered by the author to be rutile.

The honey-yellow apophyllite from Korsnäs, Finland, for which chemical, optical, and X-ray data are given, shows a complex twinning. An inner penetration twin is surrounded by two outer penetration twins. The twin laws have been established. The prism faces of the complex crystal are not (100) as conventionally taken for apophyllite but (520). The spacegroup P4/mnc commonly accepted for apophyllite could not be confirmed. It is suggested that the mineral is only pseudotetragonal, the true symmetry possibly being orthorhombic with space group Pnn2 or Pnnm.

An alkali-alumina-silica slag from the interior of a kiln used for the firing of refractories was found to contain recrystallized mullite, corundum, and beta-alumina. Isolated areas of the slag were also rich in iron oxides; in these areas beta-alumina crystallized from the melt as hexagonal plates, and at a later stage small hexagonal plates of bematite grew on the 0001 face of the beta-alumina plates in a regular fashion.

Numerous authors have attempted to use chemical composition as a means of distinguishing amphibolites derived by isochemical metamorphism of basic igneous intrusives or flows from those of sedimentary parentage. In recent years contributions have come from Engel and Engel (1951, 1953, 1962), Lapadu-Hargues (1953, 1958), Poldervaart (1953), Eckelmann and Poldervaart (1957), Wilcox and Poldervaart (1958), Evans and Leake (1960), and Walker, Joplin, Lovering, and Green (1960).

Thirty-one natural olivines, of which 25 had been previously analysed by wet chemical methods, have been analysed for Mg, Fe, Mn, Ca, Ni, and Co by electron-microprobe techniques. The totals of the olivine molecules Fo, Fa, etc., calculated from the above metals vary from 97·6 to 101·5 with a mean of 99·6%. Twenty-one of the specimens had been used previously by Yoder and Sahama to prepare a determinative curve between mole per cent. Fo and the lattice spacing d130. Yoder and Sahama had found that the data for natural olivines showed large random displacements from a straight line, and that the best straight line deviated for low Fo values from that for synthetic olivines. A plot of Fo determined from the microprobe vs. d130 corrected for lattice expansion caused by Ca and Mn shows no systematic deviation between natural and synthetic specimens, and only small deviations from the best continuous curve (maximum 4% in Fo assuming no error in d130). The maximum contents found for Mn, Ca, Ni, and Co were 3·2, 0·54, 0·33, and 0·03%, respectively. For these minor constituents, some of the wet chemical analyses agreed very well with the microprobe results while others showed large deviations. Although the substitution of Ca is small, it can affect considerably the determination of mole per cent. Fo from d130.

After specimen preparation and calibration have been carried out, microprobe analyses for most major and minor (but not trace) elements in common silicates can be made with an accuracy of about 0·5 to 5% of the amount present in about one minute for each group of three elements. Although standard chemical methods applied to large homogeneous samples will retain their fundamental reference value, microprobe techniques with their high spatial resolution, relative freedom from contamination problems, high speed, and moderate to good accuracy promise to revolutionize analytical programmes in mineralogy and petrology.

The occurrence of the minerals is reviewed. Consideration of their genesis leads to a tentative list of primary minerals, and of early diagenetie, later diagenetic and geothermal metamorphic, and late near-surface changes.