Polarized spectra (2000 to 25000 Å) have been obtained for fifteen analysed trioctahedral micas covering a wide range of compositions, and including four phlogopites, nine biotites, and two lepidomelanes. Three main contributions to the absorption have been noted: charge transfer from oxygen to ferrous iron throughout the visible and near ultraviolet, charge transfer from ferrous to ferric ions at the red end of the visible spectrum and internal d-d transitions of ferrous ions in the near infrared.

Substitutions in the brucite layer (especially Ti) cause the O → Fe2+ band to broaden, and thus to encroach on the visible region for vibration directions in the plane of the cleavage flake. The transmission window between these bands is further blocked by the Fe2+ → Fe3+ charge-transfer band, which is polarized in the plane of the flake. The overall effect is to produce very strong absorption throughout the visible region for (β, γ) vibration directions, and relatively weak absorption for α, i.e. the observed very strong pleochroism of biotite.

Many features of the spectra of chlorite, amphiboles, and tourmaline, which contain octahedral ions in brucite-like sheets, strips, and fragments respectively, may be interpreted by analogy with biotite.

Two types of solid solution effect are described: substitutional broadening, which is responsible for the extension of the O → Fe2+ band into the visible region in biotites and aluminous ortho-pyroxenes, and substitutional intensification, which permits in solid solutions transitions that are forbidden by the conventional selection rules.

A second occurrence of the mineral bolivarite has been found in the Kobokobo pegmatite, Kivu, Republic of Congo (Kinshasa). This amorphous mineral was previously considered to be evansite. Its physical properties are: weak birefringence; biaxial to uniaxial positive; n = 1·50–1·51; specific gravity 1·97–2·05; hardness 3 to 3½.

Three chemical analyses have been performed on the Congolese material. The general formula of the mineral is Al2(PO4)(OH)3.4–5 H2O. Both known bolivarites from Spain and Congo contain abnormal amounts of U. The bright green UV fluorescence is due to the presence of U. The DTA curve of the Congolese bolivarite is given. Its genesis is discussed. This uranium-bearing mineral may be an indicator of uranium mineralization in Spain.

Nepheline in a basic syenite from the Marangudzi complex is relatively Ca-rich with CaO from 1·9 to 2·4 (wt) %. This Ca-rich nepheline sometimes occurs in intimate intergrowths with plagioclase (andesine). These intergrowths are thought to have formed at temperatures in the order of 750°–850°C by resorption of plagioclase with simultaneous replacement by nepheline.

Insizwaite from Waterfall Gorge, Insizwa, is a new mineral with the composition Pt1·00Bi1·35Sb0·57. The name is for the locality and is to be applied to the end member PtBi2. The analysed material is an antimonian variety. The mineral is cubic, the unit-cell for the antimonian variety has a 6·625 (2) Å, probable space group Pa3, calc. D 12·8 g/cm3. The strongest lines on the X-ray diffraction powder pattern are: 2·96 (8) 210; 2·70 (8) 211; 2·34 (5) 220; 1·99 (10 311; 1·774 (7) 321; 1·433 (5) 421; 1·277 (6) 511, 333; 1·171 (6) 440; and 0·862 (7) 731. Under reflected light the mineral is white (in air and in oil) and is isotropic. Reflectance measurements at 470, 546, 589, and 650 nm gave 61·1, 60·0, 60·6, and 61·7 %. Micro-indentation hardness values range from 488 to 540 (av. 519) kg/mm2 with a 25 g load.

New data are presented for niggliite from the type locality and for synthetic PtSn.

Spherulitic devitrification is a post-eruptive process affecting many rhyolitic lavas of the Taupo region. The spherulites consist of cryptocrystalline intergrowths of α-cristobalite and alkali feldspar (calcic anorthoclase), with minute granules of magnetite, hematite, and secondary (?)goethite. The effects of chemical fractionation occurring during progressive spherulite growth has been studied from a suite of samples from the Aratiatia rhyolite. The most significant effect is the progressive enrichment of both bulk spherulite compositions and the coexisting residual glass in potash with increasing spherulite development. This effect is due both to the very low potash in the earliest formed spherulites and to the consistently higher Na/K ratios of the spherulites relative to the total rock compositions. These differences progressively decrease with increasing spherulite crystallization. The bulk rock compositions, however, evidently remain essentially constant. The degree of potash enrichment in the residual glasses during advanced stages of devitrification is greater than expected by reference to the ternary feldspar and quartz-feldspar systems. This post-eruptive alkali fractionation during spherulite formation is superimposed on the pre-eruptive phenocryst-liquid fractionation.

Trace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6·4; U/K (× 104), 0·7; K/Cs (× 10−4), 3·6; Th/K (× 104), 5·3; Fe2O3/(FeO+Fe2O3), 0·27) as well as 87Sr/86Sr initial ratio (0·705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis: Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history—palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.

Identification of clinopyroxene lamellae in Bushveld-type orthopyroxene from the Greenhills Ultramafic Complex has been made on the basis of partial analysis by electron microprobe as well as by unit cell determination by prolonged exposure to X-rays of single crystals of orthopyroxene. Lamellae averaging Ca42Mg47Fe11 in composition with an approximate unit cell a 9·79, b 8·90, c 5·29 Å, β 106° 14′, occur in orthopyroxene Ca2Mg67Fe31 with unit cell a 18·28, b 8·85, c 5·20 Å. The Greenhills lamellae are of orientation identical to those described by Hess (1960), which share c and b axes with host orthopyroxene.

The structural states of alkali feldspars from the eastern end of the Galway Granite show transitions from orthoclase to microcline as a result of late deformation. Analyses of twenty samples for SiO2, Al2O3, TiO2, Fe2O3, CaO, Na2O, K2O, S, Cu, Zn, Ga, Rb, Sr, Ba, and Pb agree with previously determined orders of entry of elements into the ‘alkali site’. A relationship between this order of entry and the melting points of feldspar end-members is discussed.

Three members of the pyroxene group, blanfordite, manganoan diopside, and brown manganiferous pyroxene, form important constituents of the manganese silicate rocks (gondite) of the metamorphosed manganese formations of India. The chemical composition of blanfordite is variable within the diopside-acmite series, that of the manganoan diopside corresponds to the diopside end of this series, and the brown manganiferous pyroxenes are related to aegirine-augites. The majority of the blanfordites studied have a composition within the aegirine-augite field, so that compositionally most of the blanfordites and brown manganiferous pyroxenes are similar in spite of the difference in their pleochroic schemes; The chemical composition of blanfordite varies: in association with calc-magnesian metasediments it has a high percentage of diopside, whereas in gondites and pegmatites its composition approaches more towards the acmite end. The blanfordites are often associated with manganiferous amphiboles such as juddite (manganoan magnesioriebeckite) and winchite (richterite-tremolite with blue and pink pleochroism) but never with tirodite. The brown manganiferous pyroxenes, on the other hand, are associated intimately with tirodite (richterite-tremolite with pleochroism in shades of yellow) but never with winchite and juddite.

A number of minerals and residual glasses from absarokites, shoshonites, and latites have been analysed by electron probe.

Clinopyroxenes show very little iron-enrichment and these rocks are thus distinguished from tholeiites and alkali basalts.

Glasses from this group are also distinct from tholeiites and alkali basalts and occupy a separate field on a CaO-Na2O-K2O diagram.

The crystal structure of dundasite from Gonnesa (Italy) was solved by a three-dimensional Patterson function computed using intensity data collected photographically by the Weissenberg method, and refined by successive Fourier maps and least-squares cycles to an R index 0·.066 for 505 independent observed reflections.

The chemical formula resulting from the structural analysis is PbAl2(CO3)2(OH)4·H2O. The mineral is orthorhombic, space group Pbnm, with a 9·08 Å, b 16·37 Å, c 5·62 Å. The dundasite structure consists of a three-dimensional framework of coordination polyhedra around Pb and Al. Pb ions are coordinated by nine oxygen atoms with distances ranging from 2·53 to 2·91 Å. Al ions show the usual octahedral coordination with average Al-O distance 1.90 Å. C-O mean distances are 1·28 and 1·27 Å for the two non-equivalent CO3 groups. The water molecules are not coordinated by the cations.

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.

Electron-probe data are presented for coexisting magnetite and ilmenite from seven gabbro cumulates and a gabbro pegmatite, and bulk FeO-Fe2O3-TiO2 analyses for ten magnetite-ilmenite assemblages. The oxides equilibrated at 580 to 720 °C and oxygen fugacities of 10−15·0 to 10−20·5 bar. Late-stage alteration, associated with growth of hydrothermal silicates, resulted in the breakdown of ilmenite to rutile and the dissolution of magnetite. Higher levels in the intrusion equilibrated at lower temperatures than deeper levels. All features described are consistent with the retention of the initial water content of the magma within the walls of the intrusion.

Phenocrystic and xenocrystic olivines and one olivine nodule sample, all from volcanics in the eastern Azores, range in composition from Fo87 to Fo69. Most are phenocrysts from the Nordeste alkali basaltic complex, eastern São Miguel Island, in which olivine-bearing rocks range from ankaramite to latite. CaO, MnO, and NiO trends are related to Mg-Fe contents, both for the concentrates as a whole, and also within analysed zoned crystals. It is shown that anomalous plots of Δ2ϑ(220LiF—062olivine) are related to pronounced Mg-Fe zonal gradients and, in samples from some flows, to mixtures of different generations of olivine. Regressions of Δ2ϑ vs. Fo (mol %) and FeO (wt %) for the least-zoned olivines are in close accord with those for Hawaiian olivines reported by Murata and others (1965).

MnO percentages increase linearly with FeO; this and the Hawaiian trend are indistinguishable. Limited data for the most magnesian olivines indicate that NiO increases with FeO up to ∼ 15 wt % of FeO; the trend then decreases with further iron enrichment. This trend is apparent from other olivine data, and its relationship to the onset of pyroxene crystallization is discussed. CaO in olivine phenocrysts is inversely related to normative anorthite percentages in host rocks; the trend appears to be controlled largely by co-precipitation and fractionation of calcic plagioclase.

A refinement of the crystal structure of spencerite, Zn4(PO4)2(OH)2·3H2O, was performed on a twin crystal from Salmo, British Columbia. Three-dimensional intensity data were collected by a Weissenberg apparatus. The R index was 0·098 for 335 independent observed reflections. The crystal structure previously determined is essentially confirmed. Co-ordination around Zn is both octahedral and tetrahedral. The atomic arrangement consists of complex sheets of co-ordination octahedra and tetrahedra around Zn and P atoms connected by layers of water molecules. The frequent occurrence of twinning in spencerite is explained from structural considerations.

The assemblage aluminous pyroxenes+ spinel forms reaction zones between olivine-rich and plagioclase-rich layers in the Jotunheimen complex. These zones have probably formed by cooling from high T at moderate P, passing through the ol + plag → pyroxenes + spinel reaction. The absence of garnet, which would be expected to form upon further cooling, is attributed to interruption of the cooling history by rapid uplift. This uplift is demonstrated by symplectitic breakdown of aluminous pyroxenes, with expulsion of Ts and Acm, to yield low-Al pyroxenes, spinel, and plagioclase. The uplift must be Precambrian, and suggests that the Jotun rocks were involved in rapid vertical movements long before the Caledonian thrusting took place.

The field relations, mineralogy, and petrography of a small Tertiary ultrabasic sheet are briefly described. Chemical analyses show that compositional variations exist within the intrusion and electron-probe analyses demonstrate that optically undetectable zoning is present in the olivine. Throughout the intrusion, which is composed primarily of forsteritic olivine, calcic plagioclase, and clinopyroxene, there is a differential distribution of olivine. This distribution is attributed to flow differentiation during intrusion followed by gravitative sinking of olivine crystals.

Of the metals in the series Sc, V, Cr, Mn, Fe, and Ga pyroxenes of the type LiM3+Si2O6 were obtained only from Sc, V, Cr, and Fe in dry synthesis experiments near 1000 °C. Ga and A1 gave keatite derivatives (so-called ‘β-spodumenes’) by dry heating; α-Ga-eucryptite was obtained from Ga hydrothermally at pressures between 4·5 and 6·5 kb. Mn gave Mn2O3. The lattice parameters of the pyroxenes vary irregularly with atomic number. This variation and the failure to produce a Mn3+-pyroxene can be explained by the crystal-field theory. At high temperatures A1 and Ga are too small to stabilize a silicate pyroxene phase even at moderately high pressures and form less dense tectosilicates. The octahedral stabilization energy for Cr3+ ensures that Cr, which has the same size as Ga, forms a pyroxene.

Retrograde metamorphism of gneisses and pegmatites leads in part to the destruction of feldspar and its replacement by late-stage lobate myrmekite and muscovite. Reactions promoted by retrogression suggest a range in volume of quartz production that may supplement that developed by exsolution and lead to deviations from the strict proportionality relationship suggested by previous workers. There is no need, however, to propose that quartz in myrmekite originates by constriction of pre-existing quartz within exsolved albite.

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.