Two monoclinic minerals formerly classified as ganophyllite have been differentiated on the basis of single-crystal X-ray data. True ganophyllite occurs at the Harstig mine, Pajsberg, Sweden (a, 16·60 ± 0·05 Å; b, 27·04 ± 0·08 Å; c, 50·34 ± 0·15 Å; β, 94° 10′ ± 10′; space group A 2/a), at the Benallt mine, Caernarvonshire, Wales, and in Aroostook County, Maine. Bannisterite, a new mineral, occurs at Franklin, New Jersey (a, 22·20 ± 0·07 Å; b, 16·32 ± 0·05 Å; c, 24·70 ± 0·08 Å; β, 94° 20′ ± 10′; space group A2/a) and at the Benallt mine, Wales. Both minerals have similar pseudocells: a, 5·53 Å; b, 3·3 Å; c, 25 Å; β, 94° The chemical analysis of ganophyllite from the Harstig mine, Sweden, is: SiO2, 39·67 %; Al2O3, 7·95; Fe2O3, 0·90; MnO, 35·15; CaO, 1·11; MgO, 0·20; PbO, 0·20; K2O, 2·70; Na2O, 2·18; Li2O, trace; H2O, 9·79; total, 99·85. The chemical analysis of bannisterite from Franklin Furnace, New Jersey, is: SiO2 46·20 %; Al2O3, 4·74; MnO, 23·02; FeO, 6·40; ZnO, 4·67; CaO, 1·52; MgO, 1·99; Na2O, 0·29; K2O, 1·21; H2O, 9·74; total, 99·78.

Both ganophyllite and bannisterite show a structural resemblance to stilpnome-lane from Deer Isle, Maine, in projection on selected zones. All three have a micaceous cleavage parallel to {001} in the orientations here taken. Stilpnomelane is triclinic, pseudotrigonal, and pseudomonoclinic. In the triclinic cell, a = b, 22·05 Å ± 0·06 Å; c, 17·70 ±0·06; α, 124° 49′; β, 95° 58′; γ, 120° 00′ (angles ± 5′). In the trigonal subcell, a′, 3·2 Å; c′, 36·4. Small distorted trigonal subcells for ganophyllite have a′, 3·38 Å; c′ 37·7, and for bannisterite have a′, 3·264 and c′, 37 Å.

Further data are presented on the properties of natural and synthetic members of this series. Cell constants have been determined for over 50 specimens across the composition range; the activation energy for a low-high transformation in an intermediate hyalophane has been evaluated as 101·5 ± 5·0 kcal/mole; additional single crystal studies have revealed complexities not previously reported.

Although there remain many detailed problems to be resolved, the present studies allow some suggestions concerning the nature of the relationships within the series. Problems of nomenclature and subsolidus relations are discussed together with some structural implications.

Diaboleïte has been synthesized between 25 and 100° C at atmospheric pressure and approximate water vapour partial pressures of 14·7 lb/in2. Under similar conditions at 170° C cumengéite appears to be the stable phase produced from a diaboleïte composition. Synthetic diaboleïte is much simpler morphologically than the natural mineral but the hemimorphic symmetry is more clearly demonstrated morphologically in the artificial specimens. A comparison of X-ray powder data for natural and synthetic diaboleïte shows almost exact detailed correspondence in line position and intensity between 0 and 180° 2θ. The cell dimensions obtained from X-ray powder data are a 5·869 ± 0·002 Å and c 5·495 ± 0·003 Å.

The crystal structure of gersdorffite (III) has been examined with three-dimensional Weissenberg X-ray diffraction data. The unit cell is isometric with a 5·6849 ± 0·0003 Å, space group PI, and four formula units per cell. This structure has the sulphur and arsenic atoms equally distributed over the non-metal atom sites of pyrite. All atoms show significant random displacements from the ideal pyrite positions to produce triclinic symmetry, which serves to distinguish this mineral from a disordered cubic gersdorffite (II) and a partially ordered cubic gersdorffite (I). Factors responsible for the atomic distortions are discussed.

A Tertiary dolerite plug at Carneal, Co. Antrim has been contaminated by Chalk with the production of calc-silicates and related minerals. In a larnite-spinel-rock the spinel is of the unusual ferrian variety. It has the composition The spinel, which is brown, has: n, 1·862; D, 3·97; a, 8·1905 Å. A chemical analysis and powder data are given, the implications of experimental data are briefly discussed, and the nomenclature is reviewed.

For the estimation of the properties of calcium-iron olivines in ironore sinters, synthetic mixtures of CaO, FeO, and SiO2 were prepared and melted; the obtained olivines were then examined microscopically and by X-ray powder method. The investigations allowed to state, that with the increase of the basicity of sinters, the relation of Fe : Ca in olivines decreases, which causes the change of their physical, optical, and röntgenometric properties.

The geological set-up, chemical composition, physical and optical properties, and X-ray data of one sample of chrome-chlorite (kämmererite) and of a chrome-garnet (uvarovite) from Kalrangi chromite mines, Orissa, India, are presented here. Chrome-bearing solution contributed in the formation of both the minerals in the hydrothermal stage. It is suggested that the garnet is an intermediary form between uvarovite and pyrope.

The humites are structurally analogous to olivine wherein the replacement of four oxygen by four (F,OH) anions in the slightly distorted, hexagonal close-packed array is balanced by the replacement of one tetrahedrally coordinated Si by a tetrahedral void, according to the general formula Mg2xSix-1O4x-4(F,OH)4 where x = 3, 5, 7, 9. In humites the key structural units are not ‘olivine and sellaite (or brucite) layers’, as previously assumed, but are zigzag chains of edge-sharing octahedra, just as in olivines. It is shown that for humites and olivines alike the unit cell parameters a, b, and d001/n and the cell volume (normalized to one-half the mean anion-anion distance along the normal to (001)) vary linearly with the average radius of the octahedrally coordinated cation in the chain.

Substitutions of (F,OH) for O and vacancies for Si have second-order effects on the unit cell parameters, causing a linear decrease of the normalized cell volume with increase in F/O ratio in the synthetic series forsterite-humite-norbergite. Comparison of the crystal structures of forsterite and norbergite shows that the polyhedral distortions in norbergite are smaller than in forsterite in accord with the decreased number of shared edges: the fluorines in norbergite are bonded to three Mg atoms whereas all anions in forsterite are bonded to three Mg and one Si atom.

Extensive studies on oriented reactions in the system MnO-O-H2O have revealed surprising symmetry changes, which we have been unable to explain. Orientation relationships are often complicated, but where interpretation is possible, the results support the idea that orientations are controlled by the oxygen frame-work and that considerable migration of manganese occurs.

Translation lamellae in olivine crystals are generally considered to be a result of mechanical deformation of pre-existing crystals but a recent hypothesis suggests that they may be formed during the latter stages of olivine crystallization in olivine-rich rocks due to the stresses imposed by mutual interference. Olivine crystals showing well-developed translation lamellae occur in the ultrabasic dykes of south-west Skye and it is demonstrated that these lamellae are unlikely to have been formed by mutual interference. Possible origins of the lamellae are considered and it is concluded that they are most likely to have been formed by tectonic deformation at elevated temperatures prior to the intrusion of the dykes.

Subsolidus phase relations in the systems ZnWO4-MnWO4, ZnWO4-ZnMoO4, MnMoO4-ZnMoO4, and MnWO4-MnMoO4, were investigated by using the quenching technique. A complete series of solid solutions forms in the system ZnWO4-MnWO4 above 840° C, whereas limited solid solubilities were found in the other three. The various limits of solubility are, at 620° C, 4·0 mole % ZnMoO4 in ZnWO4 and 4·0 mole % ZnWO4 in ZnMoO4, 13·0 mole % ZnMoO4 in MnMoO4 and 12·0 mole % MnMoO4 in ZnMoO4, 9·0 mole % MnMoO4 in MnWO4 and 6·0 mole % in MnWO4 in MnMoO4; and at 1000° C, 15·0 mole % ZnMoO4 in ZnWO4 and 15·0 mole % ZnWO4 in ZnMoO4, 36·0 mole % ZnMoO4 in MnMoO4 and 29·0 mole % MnMoO4 in ZnMoO4, 15·0 mole % MnMoO4 in MnWO4 and 27·0 mole % MnWO4 in MnMoO4.

Subsolidus phase relations in the system ZnWO4-ZnMoO4-MnWO4-MnMoO4 were studied at 900° C. The solubility of molybdenum in the (Zn,Mn)WO4 series increases from both end members to a maximum of 27·0 mole % at the composition Mn35Zn65. Both molybdates also have limited ranges of solid solutions, and a three-phase region occupies the central portion of the system defined by three points with compositions of 41 mole % ZnMoO4, 26 mole % MnMoO4, 33 mole % MnWO4; 57 mole % ZnMoO4, 10 mole % MnMoO4, 35 mole % MnWO4; and 27 mole % ZnMoO4, 34 mole % MnWO4, 39 mole % ZnWO4.

A 230 g kaersutite xenocryst from basalt at San Carlos, Arizona, has the composition SiO2 40·10 %, TiO2 4·44, Al2O3 14·53, Fe2O3 3·24, FeO 10·05, MnO 0·14, MgO 11·00, CaO 11·06, Na2O 2·99, K2O 1·62, H2O + 0·73, H2O − 0·10; D = 3·28; α 1·680, β 1·700, γ 1·715; a 9·858 Å, b 18·063 Å, c 5·315 Å, β 105° 14′. Kaersutite occurring as xenocrysts in basic volcanic rocks and tuffs, and as a phase in garnet-pyroxene xenoliths from such rocks, is probably of upper mantle origin, and may be the important potassium-bearing phase in this region.

The infra-red spectrum of untreated thaumasite Ca3H2(CO3/SO4)SiO4.13H2O, as well as the spectra and X-ray diffraction patterns of thaumasite heated in air at 200, 360, 550, 725, 800, 900, and 1150° C were investigated. The release of CO2 and H2O upon heating was followed. It was established that thaumasite changes between 200 and 550° C to a glass-like, amorphous state. Ca2SiO4-polymorphs and anhydrite are formed upon heating at temperatures up to 800° C. From 900° C calcium silicosulphate and anhydrite are the thermal decomposition products. These results are used in the assignment of the IR-absorption bands under 1400 cm−1 of untreated thaumasite, which are shown to be of a composite nature, i.e. attributable to overlapping vibrations of both sulphate and silicate tetrahedra.

In view of recently reported microtektites in deep-sea sediments north-west, south-west, and south of Australia, attention is drawn to the occurrence of minute forms of hay-silica glass among the products of incineration of opal-bearing vegetation in haystacks, and to the minute forms of volcanic glass ejected in lava fountains. These terrestrial micro-forms of glass have properties within the range of those for the fossil glassy bodies named ‘microtektites’. It is possible that the fusion of opal contained in silica-accumulator plants during fierce, prehistoric forest, bush, and grass fires in Australia generated micro-forms of glass that became readily airborne and drifted away in up-currents. Carried by the south-east Trades, they would ultimately descend over the Wharton Basin in the Indian Ocean. Strong to violent northerlies and north-easterlies (Brickfielder Winds) would carry them over the ocean south and south-west of Australia. Thus they could contribute to the deposits of bodies of glass regarded as microtektites in deep-sea sediments. Many microbodies of glass in the Wharton Basin could have had their origin in the Javanese volcanic eruptions.

The Benue trough is a graben structure containing folded Upper Cretaceous sediments. Mid-Tertiary to Recent rift-valley type vulcanicity in and near the trough was mainly basaltic (in the north at least), salic lavas being now represented mainly by a few eroded plugs. The Nigerian rocks are regarded as a practically extinct sub-province within a larger Gulf of Guinea alkaline province, dominated by the voluminous and still active vulcanicity of the Cameroun rift. The two structures have the same trend as other graben features further south along Africa's western margin.

Large sodic plagioclase crystals in a basalt plug within the Nigerian sub-province have rounded edges and more calcic overgrowths. They probably crystallized at deep crustal levels but are unaccompanied by any of the mafic phases that normally crystallize from basalts under high pressure. However, spinel crystals and olivine nodules found in a nearby plug indicate that the complementary mafic assemblage may be found not far away. Sparse published data on phenocrysts and inclusions in the Jos Plateau lavas offer some support for this suggestion.

Crystallization of sodic feldspars in basalt may have a bearing on the independent genesis of salic liquids, while apatite and magnetite inclusions in them suggest a possible link with carbonatites.