Contact metamorphism in the aureole of the Easky adamellite produced andalusite at the expense of regional staurolite, kyanite, and garnet. In the inner aureole sillimanite and K-feldspar also grew. Cordierite is only rarely present. Conditions of metamorphism in the inner aureole have been deduced from five independent criteria as 595 ± 30 °C and 2.5 ± 0.5kb. The nearby Lough Talt adamellite was emplaced at slightly higher pressures. Some aureole rocks have undergone oxidation with conversion of regional garnet to magnetite and andalusite. The reacting assemblage buffered ƒO2 near 10−17 bars. It is inferred that oxidation was caused by movement of H2O from the country rocks into the intrusion.

Normal carbonatite magmas are characteristically associated with ijolites and produce extensive fenitization by alkali metasomatism, commonly feldspathization or phlogopitization. The sequence of carbonatites developed from this magma are characterized by igneous isotopic ratios, high contents of incompatible elements, their distinctive pattern of differentiation from sövite to beforsite, and a late-stage rare-earth element, baryte, fluorite mineralization. Carbonatite rock is composed mainly of calcite, but fluid inclusion and related data indicate that the original magma was highly alkaline and chemically similar to that known at Oldoinyo Lengai volcano in Tanzania. It is suggested that this carbonatite magma is secondary magma produced from carbonated nephelinite magma by liquid immiscibility. Carbonatite magma can also occur associated with kimberlites but these carbonatites are alkali-poor and do not produce the characteristic fenitization.

The development of low- and hightemperature alteration products in a 23 m section of ocean-floor basalts is described. Analcime, calcite and dioctahedral smectite are ubiquitous. Trioctahedral smectite, smectite-chlorite mixed layers, chabazite and scolecite occur in the deeper sections with Fe3+ oxides/hydroxides progressively becoming more abundant in the upper regions. The upper layers of the sequence show marked chemical reduction. High-temperature chemical changes include Na and Mg enrichment accompanied by Ca and Fe2+ losses. Superimposed low temperature changes include gains in Fe3+ K, Li, and Rb, and losses in Na, Ca, and Fe2+ Many trace elements also show consistent behaviour.

Textural relationships shown by oxide phases in olivine melilitites from Namaqualand-Bushmanland, South Africa, indicate early crystallization of picroilmenite from a relatively reduced magma. Evolution of a CO2-rich vapour during magma ascent led to an increase in oxygen activity and liquidus temperatures, causing rapid crystallization of titanomagnetite. Higher oxygen activities, together with the increase in calcium activity following CO2 loss from the magma, resulted in perovskite replacing ilmenite as the stable Ti phase.

Found by J. E. DuHamel, at a prospect near Payson, Arizona, where it occurs with chrysocolla, malachite, rare fornacite, wulfenite, and bismutite. Colour chartreuse green (RHS 1A), H = 3, D = 5.80. Pleochroism in yellow weak; α = 2.08, β = 2.11. Crystals are minute orthorhombic fibres a = 7.49 Å, b = 9.66, c = 5.87, Z = 1, Dcalc 5.99 g/cm3. Strongest lines: 5.014(4), 4.828(3), 3.493(5), 3.159(7), 2.950(10), 2.642(9), 1.870(3), 1.755(3). Wet analysis (avg. of 3) gave CuO 20.4%, PbO 28.4, Bi2O3 15.9, V2O5 23.1, H2O 11.8.

Least-squares analyses of powder X-ray diffraction data have been undertaken for minerals and synthetics of composition (Mg,Mn,Fe,Co,Ni)3−xSi2O5 (OH)4. New polytypes of nepouite and greenalite have been established, and eleven new or altered unit cells have been calculated. Baumite is an unnecessary varietal name for a manganoan ferroan lizardite-1T; tosalite is an unnecessary varietal name for a manganoan greenalite; clinochrysotile is an unnecessary polytype name for chrysotile-2Mc1; orthochrysotile is an unnecessary polytype name for chrysotile-2Orc1; ortho-antigorite and ortho-hexagonal serpentine are unnecessary names for lizardite-6T1; and septechlorite should not be used. The powder data of the serpentine group are in general, poor.

Allanite phenocrysts and co-existing glass from the perlitic obsidian of Sandy Braes have been analysed for nine rare earths (RE), uranium, and thorium by instrumental neutron activation analysis and for the major elements by electron microprobe. The chondritenormalized RE plot for the allanite shows a steep slope with a negative Eu anomaly. Allanite/glass partition coefficients show a smooth variation with ionic radius (except for Eu), the variation spanning two orders of magnitude. The partitioning behaviour, which is distinct from that shown by the RE in sphene, apatite, and zircon, can be explained by the allanite structure. The pronounced affinity of the light RE for allanite makes this an important mineral in considerations of RE concentrations during the evolution of granitic liquids.

Thermal aspects of the conflicting hypotheses that the acid magmas of the British Tertiary Igneous Province were generated by either fractional crystallization of basic magmas or partial fusion of country rocks around basic intrusions are investigated by combining petrological and experimental data. Sparse large xenoliths (up to 12 m2 outcrops) of Lewisian gneiss occur in the ferrodiorite member of the Marscoite Suite in the Western Redhills Eocene intrusive complex of Skye. Most of the blocks are of granodioritic-tonalitic gneiss which is very similar to the grey gneisses of the northern and southern regions of the mainland Lewisian. One is a two-pyroxene basic granulite, closely resembling in petrography and composition the granulite-facies basic gneisses of the central region of the Scottish mainland Lewisian. During Tertiary thermal metamorphism the xenoliths recrystallized patchily to pyroxene hornfelses and up to 50% of melting occurred in any parts of blocks that were rich in alkali feldspar and quartz. Microprobe analyses of intergrown Ca-rich and Ca-poor pyroxenes in a hornfelsed ultramafic mica pyroxenite lens within a leucogneiss block give a calculated temperature of 950 °C for the Tertiary metamorphism. Melting experiments at 1 kb PH2O were carried out on leucocratic and mesocratic Lewisian gneisses (from the xenoliths), Torridonian arkose and shale. Extensive melting of the leucogneiss and arkose, to peraluminous liquids, occurs within a few degrees above their solidus (715 °C). The silicate liquidus of the leucogneiss is at 930 °C. Microprobe analyses of the glass products of melting experiments (mostly of leucogneiss) show that liquid composition trends during progressive melting are consistent with theoretical equilibria in the synthetic system Ab-Or-An-Qz-H2O. Partial fusion in the Skye Lewisian gneiss xenoliths took place at a water vapour pressure of a few hundred bars, probably under water-undersaturated conditions.

This paper presents new data on the metasomatic development of zoned ultramafic balls from Fiskenaesset, West Greenland. Field and petrographic evidence indicate retrogression of original ultrabasic inclusions in acid country rock gneisses to serpentinemagnesite assemblages, followed by regional metamorphism and consequent development of the zonal structure upon metasomatic re-equilibration via a supercritical aqueous fluid phase confined to grain boundaries. The balls show varying degrees of deviation from an ideal sequence (antigorite-talc-tremolite-hornblende-chlorite-country rock) intimated by non-equilibrium thermo-dynamics, the currently accepted conceptual framework for the discussion of diffusion metasomatism.

Major and trace-element variations behave in a similar manner to those reported from other zoned ultramafic balls but fail to define the original country rock ultrabasic discontinuity unambiguously. It is tentatively suggested that application of the apparently systematic deviations from ideality may provide additional evidence.

The presence of a hornblende zone and absence of a continuous biotite zone are two significant differences from other zoned ultramafic bodies. The former may suggest increased mobility of the aluminium species at Fiskenaesset, the latter a lower temperature of formation or smaller K2O content of the gneissic hosts.

Swing mill grinding causes appreciable oxidation of chlorite and biotite, and calcite becomes decarbonated. Magnetite is not affected. Relatively large grains can survive up to six minutes continuous grinding.

A number of geothermometers and geobarometers involving coexisting garnet, biotite, and cordierite have been used to calculate the pressures and temperatures of metamorphism of the Cashel thermal aureole in Connemara. Temperatures from the garnetbiotite thermometer show a wide variation between calibrations, and are markedly different from those obtained from the garnet-ordierite thermometer. These variations, together with the possibility of extensive reequilibration between garnet and cordierite rims and biotite, indicate that the use of exchange reaction thermometry, for these rocks at least, may be invalid. The various calibrations of the garnet-cordierite-sillimanitequartz geobarometer give reasonably consistent pressure estimates which, after allowance for partial pressures of water, indicate pressures of metamorphism of about 5±1 kb.

Two types of zoning are found in garnets from Lewisian rocks. One is due to retrogression of an earlier homogeneous garnet while the other results from growth (or equilibration) during falling temperatures. Both zoning patterns result from metamorphism during or after the Dionard tectonic phase of the Laxfordian event.

In order to be able to use the nature and scale of the exsolution microstructures developed in titanomagnetites as quantitative indicators of thermal history, it is necessary to have available accurate diffusion data for the system. Diffusion data for pure magnetite and Ti-poor titanomagnetites are available, but no data for diffusion in the centre of the solid-solution series exist. In order to obtain values for the activation energy (ΔE) and the pre-exponential factor (D0) for the interdiffusion of Fe and Ti in ulvöspinel-rich titanomagnetites, the natural microstructures developed in titanomagnetites from the Taberg intrusion, Sweden, were homogenized over a range of temperatures from 490 to 730 °C. From the model describing homogenization, values of 49.8 kcal mole−1 and 2.38 × 10−3 cm2 s−1 were calculated for ΔE and D0 respectively. Although the results obtained from these homogenization experiments are slightly less accurate than those which could be obtained by more conventional methods, the homogenization technique has several advantages which outweigh this drawback, namely the ease with which the experiment can be performed and the fact that the diffusion data can be obtained at significantly lower temperatures than is usually possible with more conventional methods.

Apatite concentrates obtained from a carbonatite of the Tororo complex contain cogenetic fluid and solid primary inclusions. The solid inclusions are commonly composed of calcite and shortite and these minerals, together with the host apatite, were deposited from aqueous fluids at approximately 400°C.

A set of pyribole structures can be derived from a model I-beam containing two distinct silicate chains in which the tetrahedra are rotated by different amounts. The model allows some tetrahedral distortion and is not bound by the parity rule (Thompson, 1970). A subset of pyribole structures which includes all the commonly occurring types can be defined using a new rule: that the structure may contain two types of tetrahedral layer, but no tetrahedral layer may contain two types of tetrahedral chain. This rule is more fundamental than the parity rule and has its origin in the optimization of the edge-to-edge packing of the tetrahedral chains into layers. Pnm21 (amphibole) and Pbc21 (pyroxene) emerge as space groups for ‘low protopyriboles’. The approach used here leads naturally to the − and × -chains notation of Thompson used by Veblen and Burnham (1978).

Minute crystals of columbite occur in tungstate ore in the quartz veins at Carrock Fell Mine. Accompanying wolframite crystals show pronounced niobium enrichment adjacent to growth faces. The columbite grains, however, occur as inclusions in minerals formed during metasomatic replacement of the wolframite. They are chemically variable, containing 7–18 % WO3 by weight, up to 1.9% Sc2O3, and up to 4.7% TiO2. Tin, a common minor element in columbite, was not detected. The columbite grains are spatially associated with carbonate minerals involved in wolframite replacement, and it is suggested that their formation occurred principally when carbonate precipitation caused a reduction in the stability of dissolved niobium complexes.

The authors report the first occurrence of awaruite in Pakistan, in the Sakhakot-Qila ultramafites. Electron-microprobe analysis reveals a considerable variation in the compositions of awaruites from different parts of the complex. The presence of copper in awaruite, in amounts up to 5 atomic percent, is also reported for the first time. In one chromitite body, an iridian awaruite with up to 27 wt% of iridium occurs in association with ‘normal’ awaruite and a new Ru-Os-Ir-Ni-Fe alloy. The awaruites are discussed in relation to those from other localities.

New X-ray and optical studies show that thomsonite has a < b < c and its optical orientation is α = b, β = c, and γ = a. The refined cell dimensions of Old Kilpatrick thomsonite are a = 13.051, b = 13.092, and c = 13.263 Å. The systematic absences h+l odd for h0l, h + k odd for odd for hk0, and l odd for 0kl uniquely determine the space group as Pcnn for which the arrangement of the alumino-silicate framework is suggested. The exceptions to the above absences are the 704 reflection (due to Renninger effect) and many weak hk0 reflections which suggest that the space group might be Pcnm or Pcn2. The observed habit, cleavage, and parallel growth are discussed in the light of the proposed framework structure.