Rhodonite, rhodochrosite, spandite, psilomelane, beldongrite, braunite, sitaparite, and vredenburgite from a collection hy Fermor have been studied by the X-ray powder diffraction method. The cell dimensions of all forms of eryptomelane—massive, horny, botryoidal, reniform, mamillated, and stalactitic—are a = 9.82 Å., c= 2.86 Å.. whereas the cell dimensions of shiny pitch-like beldongrite are a= 9.82 Å., c= 2·87 Å. The amorphous admixture associated with cryptomelane is revealed by a broad halo, 4·60 Å. to 3·90 Å., in the powder pattern. Aminoff's crystal data for braunite are discussed with a different orientation, and a new space group, I 4/mmm, is assigned after indexing the powder pattern. Fermor' sitaparite (bixbyite) is assigned a new space group Im3 , different from that proposed by Pauling et al., on the basis of a fresh indexing of the powder pattern. Manganese-garnet from the gondite series has a cell-size of the order of spessartine, whereas the cell-size of manganese-garnet from the kodurite series varies from 11·72 to 11·95 Å. Fermor's spandite from the kodurite series is a mixture of spessartine, grossular, and andradite garnet-molecules with almandine and pyrope as minor components. Ramsdellite and γ-MnO2 or β-MnO2 are found in a number of samples of manganese ores.

Simple chemical procedures (colorimetric and gravimetric) for the determination of Co, Cr, Cu, Ga, Ni, P, and S in an iron meteorite or in the separated metallic phase of a pallasite are described; the minimum size of sample is discussed. A procedure for the quantitative removal of the metallic, sulphide, and phosphide phases from a stone or siderolite is described, and is applicable to the quantitative isolation of silicate and oxide inclusions from siderites (other than some very high in nickel).

The mineral assemblages developed in a variety of high-grade metamorphic rocks from southern Nyasaland are compared with standard metamorphic facies mineral assemblages proposed by some authors.

Infra-red absorption spectroscopy has been used to study the retention of hydroxyl groups by kaolinite and halloysite after heat treatment in the range 600° C. to 850° C. Structurally disordered specimens initially lose water more rapidly than do ordered specimens, but retain hydroxyl groups at higher temperatures. Work on the phases obtained above 1100° C. is incomplete, but results for the lower temperatures indicate that the ordered structures tend to retain their atomic arrangement and form metakaolin, whereas disordered structures readily rearrange to yield γ-alumina, to the formation of which water is probably essential.

The presence of pyrosmalite is recorded in a metasomatized slate that is in contact with intrusive rhyolite in the Nant Francon area of North Wales.

Specimens of kaolinite have been found in inclusions in the ferruginous deposits on the Yorkshire Coast, just north of Scalby. The excellent quality of the X-ray powder pattern suggests that this kaolinite is better crystalline than kaolinites from other localities. Although the lattice constants of the Scalby material are considered to be identical with those previously published for kaolinite, minor differences in the intensities of the X-ray reflections do occur and may be due to a less distorted structural layer in the Sealby kaolinite.

A differential thermal analysis curve of thaumasite shows an endothermal peak at 206° C., correspinding to the loss of H2O and CO2, and a weak exothermal peak at 709° C., corresponding to recrystallization to a mixture of anhydrite and larnite, as is shown by X-ray powder photographs of material heated to 950° C. Improved powder data for thaumasite are given: the three strongest lines are at 9·66, 3·79, and 4·58 Å., and the cell-dimensions are a 10·992, c 10·311 Å.

Experimental data in the system CaO-MgO-FeO-SiO2 suggest that there may be a plateau on the liquidus and solidus of the multicomponent system basalt-peridotite. If this is so, fusion of peridotite would produce only basaltie magmas over a wide temperature range; when the temperature reached a value such that the liquid crossed the threshold of the plateau, there would be a rapid increase in the amount of fusion for small temperature increases, with the formation of picritic magmas; basaltic magmas containing suspended forsteritic olivine crystals could dissolve them if the temperature rose slightly above that of the plateau threshold; a high proportion of a picritic magma would crystallize in a small temperature interval, with the precipitation of forsteritic olivine that was only slightly zoned. These possibilities are compared with current theories, and it is concluded that several petrological axioms may require critical re-examination. An experimental procedure is outlined to determine the shape of the liquidus and solidus in the basalt-peridotite system.

An elongated boss of alkali dolerite is described having a NW. trend and measuring 800 m. by 250 m. Two main rock-types occur, an ophitic feldsparrich analeime-olivine-dolerite or leucodolerite and a tesehenite with subhedral pyroxene. The second type is intrusive into the first but the two are associated in vertical veins. Both show local banding and analcime-nepheline-syenite forms a differentiate of both. Finer grained olivine-rich dolerite resembling the crinanites of Jura occurs at the NW. extremity of the boss and probably represents the original magma. All four types have been analysed and are thought to be the products of normal crystal fractionation with slight absolute iron enrichment. The boss was apparently headed not far above the existing exposures and is considered to be of Tertiary age. The pyroxene and olivine of the leucodolerite have been separated and analysed.

An unusual monazite deposit of metasomatic origin is described. The monazite occurs as randomly oriented crystals in a dolomitic marble. The chemical composition and optical data of the monazite are given.

Attention is drawn to anomalies in the nomenclature of the niobatetantalates, and the fergusonite series as used by Dana is renamed the fergusonite-formanite series. Chemical variations in this series are discussed with particular reference to H2O, Ca, Ti, Yt, individual lanthanons, Th, and U. Members of the series usually show heavy lanthanons exceeding light lanthanons but one specimen shows high Gd+Tb+Dy.

Uraninite from Geevor Mine, Cornwall, has been analysed by the complete lead method and an age of 290±7 million years has been accepted. Similar studies of uranium from Tyndrum Mine, Perthshire, give an age of 230±8 million years. The significance of the results is briefly considered.

The gels prepared by adding ammonium hydroxide rapidly to ferric chloride solutions to various pH values are shown to consist of amorphous material and crystalline goethite ; no other iron oxide was definitely identified in the present experiments, although this does not preclude other oxides being present in gels prepared under slightly different conditions. The goethite grows as acieular crystals on ageing at all pH values, but the rate of growth is greater at higher pit values. The exothermic peaks appearing on differential thermograms of such gels are apparently due to coalescence of extremely minute hematite particles to give larger particles, the sharpness of the peak indicating to some extent the size of the original hematite particles. These observations are related to data for other iron oxides, and the morphology of ferric oxide polymorphs under the electron microscope is considered.

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.

Uigite from Uig in Skye described by M. F. Heddle in 1855 has proved on examination to be thomsonite (var. faröelite).

A new method is described to replace the standard procedure for completing the adjustment of an optical symmetry plane, with conditions for the accurate use of the biquartz. Extinction measurements are plotted to show the wide range of sensitivity (for the adjustment of A1 and A2) at various directions in the symmetry planes of a plagioclase. It is proposed that A1 and A2should be adjusted at different settings of A4 so as to obtain maximum sensitivity for each of those axes.

The problem of silicate immiscibility, of petrological and technological interest, is discussed in terms of the structures of silicate crystals and certain phase diagrams. Physical chemical principles are employed to indicate the author's basis for suspecting that certain structures in the crystalline solid are carried over into the melt and are a major contributory cause of silicate immiscibility. These structures appear to be limited to the neso (SiO4)4−, soro (Si2O7)6−, cyclo (Si3O9)6−, and ino (SiO3)2− types of silicate polymers and do not include the more complex phyllo- and tecto-silicate polymers.