Yttrotungstite occurs at Kramat Pulai mine, and at Tapah, Kinta, Perak, Malaysia, as yellow earthy material and as monoclinic laths, elongated along [001], flattened, and always twinned, on {100} to pseudo-orthorhombic symmetry, and frequently bevelled by {110}; crystals are very rarely terminated by {101}. γ = [010], α:[001] = 26°, probably in β acute, and 2Vα ≃ 68°. A thermal weight loss curve and an infra-red absorption spectrum are given and discussed. Accessory minerals include raspite and stolzite.

The yttrotungstite unit cell has a 6·95, b 8·64, c 5·77, β 104° 56′, space group P21/m; cell contents are (Yt, Ln, Ca, Mg)2(W, Al, Si, Ti, Fe)4(O, OH)14(OH)2·2H2O. Indexed X-ray powder data are given. Microprobe studies show that Al and Si replace W and are concentrated in zones showing larger values of a sin β (6·75 Å instead of 6·72 Å) but with no other appreciable difference in cell dimensions. Crystal structure studies show that the structure consists of WO6 octahedra sharing non-opposite edges in zig-zag chains running parallel to [010]. Yttrium is in approximately trigonal prismatic coordination between the chains, with the water molecule as a seventh neighbour at one prism face. The water molecule is accommodated in the angle between zig-zags in the WO6 chains; it is probably hydrogen bonded to chain oxygen atoms, and becomes coordinated to the yttrium by a shear between chains away from strict close-packing of the oxygen atoms. The shear is related to the change in a sin β in (Al, Si)-rich zones; arguments based on this and on details of the chemical analysis suggest that SiO4 replaces WO6 with a local oxygen deficit.

Oxygen atom peaks on partial Fourier difference syntheses for our data for yttrotungstite are only slightly larger than the troughs in the syntheses due to experimental error. Methods of testing the significance of the positive peaks are described in an appendix.

The crystal structure of coalingite (Mg10Fe2(OH)24(CO3)·2H2O) has been determined using single-crystal X-ray methods. The mineral is trigonal, with space group Rm, aH = 3·12, cH = 37·4 Å, Z = ½, and (0001) cleavage. The structure is of a layer type, and is based on a structural element about 12·5 Å thick in the c-direction and consisting of two brucite-like layers and one disordered layer containing carbonate ions and water molecules and resembling those in sjögrenite and pyroaurite. The unit cell comprises three of these structural elements stacked together in the c-direction. The Mg2+ and Fe3+ ions are randomly distributed among all the octahedral sites of the brucite-like layers. The structure closely resembles those of sjögrenite and pyroaurite, but has two brucite-like layers between each CO32−−H2O layer where these have one. There is a tendency to random interstratification, and the crystals appear to contain intergrown regions of brucite and of sjögrenite or pyroaurite. Coalingite-K probably has a similar structure, but with three brucite-like layers between each -H2O layer; its idealized formula is probably Mg16Fe2(OH)36(CO3).2H2O.

K-feldspar variation is described for four salic plutonic igneous complexes that show normative mineral variation in keeping with the course of fractionation predicted from experimental studies. These are a sodic syenite (Loch Ailsh), potassic syenites (Loch Loyal), a peralkaline syenite and soda granite complex (Puklen), and a calc-alkaline pluton (Foyers). Additional data are given for examples from the literature. Microcline becomes more abundant relative to orthoclase as members of these intrusive sequences approach thermal minima on the liquidus in the system Ab-Or-An-Qz. This relation exists irrespective of the compositional range of the rock suites, the bulk composition of the alkali feldspars, grain size, or field relations. Early orthoclase-bearing rocks retain orthoclase when enclosed as xenoliths in microcline-bearing rocks, or when cut by minor bodies of microcline-bearing rocks. The K-feldspar variation may reflect increasing water content or the peralkaline or peraluminous character of the fractionating magmas. These factors affect the feldspar structure at the time of initial crystal growth and dictate whether microcline will develop on cooling.

Pyrophanite was found in quartz-rhodochrosite veins in hornstones of Algonkian pyritemanganese ores. Photometric reflectance falls from R0 24 and RE′ 19 at 405 mµ to R0 18 and RE′ 15% at 656 mµ (in air). Vickers microhardness (100 g load) demonstrates directional anisotropy, the average value is 611 kg/mm2. Besides the main constituents, subordinate to trace quantities of Mg, Si, Al, Ca, and Cu were recorded by a spectrographic analysis. Unit-cell dimensions are a = 5·131 and c = 14·27 Å. Electron-microprobe analysis gave MnO 43·3, FeO 3·8, MgO 0·05, TiO2 52·9, SiO2 0·1, total 100·15%. The origin of the Chvaletice pyrophanite was most probably connected with a hydrothermal metamorphism of an Alpine-paragenesis type. The source of elements was older sedimentary, basic volcanic, and metamorphic mineral assemblages.

The upper stability of margarite has been determined to be 450 °C at 1 kb and 530 °C at 2 kb total pressure (PH2O = Ptotal). Other experiments delimit in a general way the lower stability of this mineral and its paragenesis in more SiO2 rich compositions. The presence of the 060 reflection at 1·475 Å can be used to distinguish between margarite and paragonite or muscovite.

The angular relationships among sets of olivine plates in barred chondrules were investigated on the universal stage to test a suggestion that such chondrules represent exsolution and inversion from a pre-existing jadeitic pyroxene. In one of sixty-seven cases studied, adjacent plates represent olivine twinning on (100); the others vary randomly and correspond to neither olivine nor pyroxene twinning. On this basis and from other evidence, we conclude that the mineralogy and texture of barred chondrules are primary and due to rapid crystallization of ultrabasic magma in a low-pressure environment.

Chemical analyses and physical properties are given for six samples of beryl from greisenized granites, pegmatites, and beryl-quartz veins in the Rosses granite complex. The beryls studied were all very similar in composition and contain significant amounts of alkali elements and water in addition to the constituents represented by the formula Be3Al2Si6O18. Calculation of the empirical unit cell contents indicates that most of the H2O+ is present in the mineral as water molecules. The effects of these extra constituents on the physical properties are discussed, and it is suggested that the variation in refractive indices displayed by beryl is to a large extent attributable to the variable water content.

Sitathali is an olivine-bronzite chondrite, consisting largely of olivine (Fa18) and orthopyroxene (Fs19) with minor amounts of a clinopyroxene (Ca36Fe12Mg52), plagioclase (An12), nickel-iron, troilite, chromite, and a phosphate (apatite or merrillite). The chemical analysis of a 4 gm sample gave SiO2 39·85, TiO2 0·10, Al2O3 2·84, Cr2O3 0·35, FeO 13·27, MnO 0·28, MgO 23·01, CaO 1·84, Na2O 0·65, K2O 0·15, H2O+ 0·23, H2O− 0·05, P2O5 0·25, FeS 5·09, Fe 10·22, Ni 1·58, Co tr. total 99·76. The metal displays Neumann bands, some deformed, as well as areas of apparent flowage. Troilite locally exhibits twin lamellae and in places replaces kamacite in the plessite fields. Elsewhere it is in braided veinlets and globules, both reflecting former melting. The varied textures suggest a complex post-formational history encompassing several deformational events presumably due to breakups and possible extraterrestrial impacts.

The one-atmosphere experimental melting and crystallization relations of some basic lavas of Réunion Island, Indian Ocean, are investigated. They comprise products of the extinct volcano Piton des Neiges and the active volcano Piton de la Fournaise. New data and interpretations are presented for the 1939 oceanite and its contained glass, originally described by Lacroix (1939a). The liquidus v. iron enrichment curves for these Réunion lavas fall about 20 °C above those of the lavas of Kilauea, Hawaii. The primitive liquid reaching the surface contained about 10 % MgO.

From thermodynamic considerations of the system anorthite-åkermanite it appears that the effective molecular weights of the ‘molecules’ in the melts of this system are 0·5 the molecular weights of anorthite as well as that of åkermanite.

The effective molecular weight value of 0·5 anorthite is in significant contrast to that of 1 anorthite obtained by Adams and Cohen (1966) from a similar analysis of the system anorthite-diopside (Bowen, 1915, and Osborn, 1942). The analysis by Adam and Cohen would lead to a non-ionic silicate melt structure in the system anorthite-diopside in contrast to the accepted electrolytic view of silicate melts. It is suspected that the reason for this apparent difference lies in the published liquidus morphology of the anorthite primary fields of the system anorthite-diopside. This same liquidus morphology is also responsible for the distortions in the isofracts and isotherms in the high-temperature area of the primary field of anorthite of the system anorthite-åkermanite-diopside (de Wys and Foster, 1958).

Aluminium hydroxide gels have been prepared by the hydrolysis of amalgamated aluminium in water and by precipitation from aluminium salt solutions with an anion exchange resin in the hydroxyl form. The products crystallizing from such gels have been examined by electron microscopy and by X-ray and electron diffraction. Bayerite crystallizes as cone or pyramid-shaped particles and gibbsite as hexagonal plates or prisms. Two types of gel are postulated. The first type, pseudoboehmite, predominates in the absence of acids, is uncharged and rapidly crystallizes to bayerite; the second type, pregibbsite gel, occurs in carboxylic acid solutions, is positively charged and, in the absence of inorganic anions, crystallizes slowly to gibbsite.

Seventy-nine black tourmalines collected over a 12 000 km2 area of Precambrian to lower Palaeozoic rocks in northern Nigeria show a close correlation between maximum R.I., absorption colour, and occurrence in non-feldspathic micaceous schists and schorl rocks on the one hand, and in gneisses, migmatites, and feldspathic pegmatites on the other. Pleochroism is known to depend upon the total iron content and the Fe2+Fe3+ interaction. Colour variations may thus provide useful indicators of the geochemical environment during crystallization.

Limited published data, supplemented by additional measurements on four tourmalines from outside the original area, suggest that similar correlations would be obtained for the rest of Nigeria.

Selective processes of boron metasomatism may have been important in the association of different coloured tourmalines with feldspathic and non-feldspathic rocks, and the apparent lack of biotite in most tourmaline-rich rocks. The source of the boron probably lay within the upper Proterozoic to lower Palaeozoic metasedimentary belts with which the tourmaline is most strongly associated.