Experimental data from the system CaO-MgO-Na2O-Al2O3-SiO2 and from the system CaO-MgO-FeO-Al2O3-SiO2 are used to show the nature of the changes in composition, with temperature and with pressure, of liquids in equilibrium with augite, plagioclase, and olivine as MgO in the system CaO-MgO-Al2O3-SiO2 is partially replaced by FeO and as Na2O replaces CaO. As differentiation of tholeiitic basalts proceeds, Fe/Mg increases, Na/Ca increases, and normative hypersthene increases and these effects alter the solubilities, and hence the proportions of augite, plagioclase, and olivine which co-precipitate. In particular olivine becomes more soluble (less is precipitated) as Fe/Mg increases; plagioclase becomes more soluble but augite less soluble as Na/(Na + Ca) increases; augite also becomes less soluble as normative hypersthene increases, and as pressure is reduced during ascent.

Experimental data from remelted ocean tholeiites encounter the same equilibrium and are presented and compared with the data from synthetic systems.

Some natural examples of daughter liquids related to parents by crystallization of augite, plagioclase, olivine, are combined with the experimental data and with some model calculations to demonstrate that only a very limited range of proportions of augite : plagioclase: olivine (approximately 30 : 50 : 15 to 20 : 60: 20) produces daughter liquids which lie on the major element variation of the tholeiitic basalt series. Other proportions lead to daughter liquids which are not basalts. In the light of these restrictions, several recent publications are reinterpreted as examples of fractionation of augite, plagioclase, and olivine, rather than examples of partial melting. The recognition of the small effect that massive (50 to 83%) crystallization has on basaltic chemistry by contrast with the large effect that small accumulations of phenocrysts can have is particularly emphasized in this reinterpretation.

Comparisons and possible relationships are suggested between some low-K2O, low-TiO2 tholeiites; some calcic-, aphyric-, dykes of some tholeiitic provinces; some chilled margins of some layered intrusions; some basalts from Iceland, and some basalts from the ocean ridges.

Both Species were Found as post-Mine Minerals in the Lone Pine mine, Catron County, New Mexico. They occur encrusting ores of fluorite-pyrite with khademite and gypsum.

Wilcoxite is clear, colourless to white, H = 2, D = 1.58. Abundant as spongy masses of perfect to somewhat rounded crystals. Stubby prisms are bounded by {100}, {010}, {110}, {10}, and {01}. Triclinic P or P1 with a = 14.90, b = 6.65, c = 6.77 Å, α = 117° 26′, β = 100° 35′, γ = 80° 10′, and Z = 1. Strongest lines are 5.654(9) 110, 11, 4.908(10) 11, 4.371(6) 201, 210, and 3.384(5) 11, 111. Biaxial negative with α = 1.424, β = 1.436, γ = 1.438, 2Vα = 48°. Analysis gave MgO 6.61%, Al2O3 8.13, Fe2O3 0.46, MnO 0.13, SO3 27.50, H2O 56.40, F 3.48, total 101.24 (corr. for O ≡ F) leading to MgAl(SO4)2F·18H2O.

Lannonite is usually as chalky white aggregates of microscopic tetragonal (square) platelets; H = 2, D = 2.22. Indexed as tetragonal a = 6.84, c = 28.01 Å, and Z = 1. Strongest lines are 13.98(10) 002, 4.840(7) 110, 3.980(5) 116, and 3.456(7) 017. Uniaxial positive with ω = 1.460 and ε = 1.478. Analysis gave CaO 12.06%, MgO 4.46, Al2O3 11.06, SO3 34.40, H2O 32.00, F 9.44, total 99.45 (corr. for O ≡ F) leading to HCa4Mg2Al4 (SO4)8F9·32H2O.

Both minerals and mineral names have been approved by the Commission on New Minerals and New Mineral Names, IMA.

New analytical data for the khademite associated with these species are presented.

Tetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, and X) affect the tilting and distortion is critically reviewed. Although P, T, and X are generally regarded as analogous variables in their effect on framework structures there is reason to believe that they have different structural effects. In particular, an important, and frequently neglected, thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. The effects of P, T, and X on displacive transformations in framework compounds are reviewed with particular reference to the disordered alkali feldspars and the leucites. It seems probable from the available evidence that displacive transformations do not take place at a critical size of the framework. Displacive transformations can take place with or without a volume discontinuity and hysteresis. Furthermore, the effects of P, T, and X on a solid-solution series with a displacive transformation can be different, one variable causing a volume discontinuity and another a smooth transition.

The kinetics and mechanisms of pentlandite [(Fe,Ni)9S8] exsolution from the monosulphide solid solution [or MSS (Fe,Ni)1−xS] have been studied by synthesis and annealing experiments in part of the Fe-Ni-S system particularly relevant to sulphide nickel orebodies. This experimental work has been combined with the examination of the compositions and textures of pyrrhotine-pentlandite intergrowths from a variety of ore deposits. Isothermal annealing of MSS compositions with varying M:S and Fe:Ni ratios at 400 °C shows the formation of a sequence of textures which depend for their full development chiefly on initial M:S ratio and annealing time. The full sequence of textures starts with heterogeneous nucleation of pentlandite at MSS grain boundaries, the growth of these blebs to form ‘rims’, nucleation of finer bladed particles arranged ‘en échelon’ along fractures, and, finally, homogeneous nucleation of fine orientated pentlandite lamellae. Using the information from the annealing experiments, the inter-growths produced by cooling in the natural ores are interpreted using a simplified Time-Temperature-Transformation Model.

Buddingtonite of similar composition and properties to that described from the type area, is uniformly distributed throughout the upper 600 m of strata in the Condor Oilshale Deposit near Proserpine, Queensland. The mineral, which constitutes up to 16% and averages nearly 10 % of the strata, is associated with abundant montmorillonite, siderite, and quartz as well as minor amounts of disordered kaolinite, illite, calcite, pyrite, cristobalite, and an unnamed species of the jahnsite group. The buddingtonite is concluded to be of diagenetic origin. It developed in an ammonium-rich environment, most probably at significant depth within the mud beneath a stratified lake. Its progenitor, however, remains unknown. The occurrence of this mineral is also of interest in that ammonia could prove an important by-product in the commercial exploitation of the oilshales.

Eluvial pebbles from the Afu Hills, Nigeria, are largely composed of fluocerite, Ce0.50La0.28Nd0.11 Pr0.04Th0.03Ca0.02F3, with minor monazite. The fluocerite shows two types of alteration, to bastnäsite, and to bastnäsite-(La) with cerianite. Electron microprobe analyses are given for fluocerite, monazite, bastnäsite and bastnäsite-(La). The refined cell parameters of the fluocerite are a = 7.130±0.001, c = 7.2985 ± 0.001 Å. Strongest lines are 3.204 Å (100), 3.65 (45), 2.059 (45), 2.010 (45) and 3.565 (40). Space group P 63/mcm, Z = 6, Dcalc. = 6.12 g cm−3, ω = 1.613, ε = 1.609 both ±0.002, uniaxial negative. For bastnäsite a = 7.131 ± 0.002, c = 9.786±0.004 Å, for cerianite a = 5.460 ± 0.005 Å.

A high-pressure modification of NaAlSiO4, with the calcium ferrite structure was synthesized at pressures higher than 24 GPa using a double-stage split-sphere type high-pressure apparatus. The unit cell dimensions are: a=10.1546(8), b=8.6642(8), c= 2.7385(4) Å, and V = 240.93(3) Å3 with the space group Pbnm. Calculated density is 3.916(1) g/cm3. The crystal structure was determined by the ordinary powder X-ray method. Both M1O6 and M2O6 octahedra run parallel to the c-axis, forming edge-shared double chains. The shared edges exhibit remarkable shortening (2.25–2.39 Å). Sodium atoms are located in the ‘tunnel’ formed by the linked double chains, being in eightfold co-ordination. The structure is very similar to that predicted by Dempsey and Strens (1976) with the aid of the DLS method. The possible instability of the calcium ferrite type of Mg2SiO4 is discussed.

Microprobe analyses of members of the erlichmanite-laurite series from Guma Water and Senduma, Sierra Leone and Tanah Laut, Borneo, indicate that complete solid solution is possible between OsS2 and RuS2 with considerable substitution of Os and Ru by Ir, Rh, and Pt. The cell size of the erlichmanite from Guma Water is a = 5.6183±0.0003 Å at a composition (Os0.61Ru0.30Ir0.06Rh0.03)Σ0.93S2 whilst the laurite from Senduma has a composition of (Ru0.88Os0.05Ir0.04 Rh0.03)Σ0.93S2 and a cell size of a = 5.6089±0.0005 Å. Substitution of Os for Ru provides the predominant cause of the variation of cell size. Substitution by other elements of the platinum group appears to produce little effect on cell size and is presumably controlled by genesis rather than considerations of crystal chemistry or structure. The recorded analyses for these elements indicate a pre-dominance of Ir over Rh for members of the series containing more than about 15% of the laurite molecule. For the remainder of the series Rh is more important than Ir. The reflectance in air and oil of the members of the series from Sierra Leone and Borneo are presented and the microhardness of the erlichmanite from Guma Water shown to be 1854 kg/mm2. This is the first report of laurite from Senduma, Sierra Leone.

Evidence obtained from morphological and extensive trace element studies, and from the examination of mineral and fluid inclusions in Witwatersrand pyrites, shows three major types of pyrite: (i) detrital pyrite (rounded pyrite crystals transported into the depositional environment); (ii) synsedimentary pyrite (round and rounded aggregates of fine-grained pyrite formed within the depositional environmen); and (iii) authigenic pyrite (newly crystallized and/or recrystallized pyrite formed after deposition). The detrital grains contain mineral inclusions such as biotite, feldspar, apatite, zircon, sphene, and various ore minerals, and fluid inclusions with daughter minerals. Most of the inclusions are incompatible with an origin by sulphidization. Recrystallized authigenic pyrite occurs in large quantities but only in horizons or localities which have been subjected to higher temperatures during the intrusion or extrusion of younger volcanic rocks. Important additional findings are the often substantial amounts of pyrite and small amounts of particles of gold found in Archaean granites (Hallbauer, 1982) as possible source rocks for the Witwatersrand detritus. Large differences in Ag and Hg content between homogeneous single gold grains within a hand specimen indicate a lack of metamorphic homogenization. The influence of metamorphism on the Witwatersrand pyrites can therefore be described as only slight and generally negligible.

Borehole samples from the Wildmoor Sandstone Formation have been analysed for whole-rock major and trace elements and the mineralogy determined by X-ray diffraction and conventional thin sections. The forty-two samples studied were obtained from boreholes drilled in a long established effluent site and from control boreholes away from the site. Elements are associated with one or more of calcite, quartz, K-feldspar, and clay plus oxide. The most important mineralogical change due to current infiltration is progressive loss of calcite. Background element concentrations are established and only Pb, and in one sample Cu and Zn, are found in higher concentrations representing anthropogenic additions to the system.

The first occurrence of thaumasite resulting from seawater-basalt interaction has been discovered in a drill hole on Mururoa atoll (French Polynesia, South Pacific). This sulphate-carbonate-silicate is associated with zeolites (phillipsite, chabazite, gmelinite), apophyllite, analcime, and gyrolite. In this environment thaumasite can be considered as the last mineral of an alteration sequence. It crystallized from a Ca-SO3-CO2-rich and Al-Na-K-poor fluid. The temperature of this solution is unknown, but was probably not greater than 100°C.

The chemistry of spinels, plagioclase, and iron-rich, normally zoned pyroxene and melilite from some metallurgical slags has been investigated by electron microprobe analysis. Minor element partition coefficients, some of which are composition-dependent, have been calculated from the analytical data. The pyroxene/liquid partition coefficients range from 4.03 to 0.03 in the order Ti/Zr, Al, Mn, Zn, Ba, Sn, Na, reflecting increasing incompatibility. The spinel/liquid partition coefficients range from 40.89 to 0.02 but in the order Ti, Ni, Mg/Zn, Al, Mn, Cu, Sn, Zr. However, Sn becomes very compatible when the pyroxene and spinels crystallize in association with cassiterite. Melilite greatly discriminates against the incorporation of minor elements into its crystal structure. The crystallization of these phases produces residual liquids enriched in Na, Mn, Zn, Sn, Ba, W, and Pb.

Ion microprobe analyses of Li are presented for minerals of the Variscan granites and related rocks of west Cornwall. Together with electron microprobe data these provide insight into the behaviour of Li during the protracted late- and post-magmatic history of the granites. The role of the Mg-Fe tourmaline series is emphasized in this exploratory study.

Clinopyroxene solid solutions crystallized at Ptot = 2 kbar in the natural system phonolitic tephrite-H2O (lava type from Etna eruption 1971) indicate a linear increase of ln Xcpxcats with H2Oliq %. After coupling this with the In Xcpxcats pressure dependence found through experiments, a simple relation has been set up for clinopyroxene- and plagioclase-bearing magmas. This relation allows us to calculate the amount of water dissolved in the melt, at any known pressure in the crustal range.

Sulphur isotope ratios in sulphides and baryte from stratabound and stratiform orebodies in a metavolcanic-sedimentary sequence in Namaqualand were found, in part, to be extreme for Precambrian sulphur. Black Mountain, Aggeneys, in the west gave an average for the sulphides of δ34S = +8.9±3.7‰ (9 samples), an average for barytes of +20.6±4.3‰ (3 samples). Broken Hill, Aggeneys, in the centre gave an average for the sulphides of δ34S = +19.8±3.1‰ (19 samples). Gamsberg, in the east, gave an average for the sulphides of δ34S = +29.2±1.8‰ (24 samples), and an average for barytes of +35.4±0.2‰ (2 samples). The δ34S values increase eastward. Their range is strongly on the positive side and does not centre around zero. The Gamsberg barytes and most Gamsberg sulphides have more positive δ34S values than those reported for other Precambrian sulphides and sulphates. We interpret the above sulphur isotope range as being mainly due to the varying contributions of submarine-exhalative sulphide sulphur with δ34S close to zero and bacterially(?) reduced sulphate with strongly positive δ34S, apparently from evaporites in the east. Metamorphism of amphibolite facies grade has partly isotopically re-equilibrated the ore minerals, as indicated by galena-pyrrhotine and sulphide-baryte isotope temperatures from single specimens, but has not destroyed the primary sulphur isotope range indicating pre-existing sulphate concentrations.

Infrared spectroscopy affords a rapid and easy method of estimating the position of a mineral in the olivenite-adamite solid solution series, and of estimating the amount of phosphate substitution in olivenites. Toman's discovery of the monoclinic symmetry of olivenites with up to approximately 20 atom % Zn/(Cu + Zn) has raised a problem in nomenclature. It is suggested that the definition of ‘cuproadamite’ be extended to cover all orthorhombic members of the series containing appreciable Cu. Studies of deuterated materials have helped to solve some of the absorption band assignments for olivenite-adamite, libethenite and related minerals.

Sphalerite is a common constituent of the mineralized rocks and host metasediments of the Foss baryte-base metal deposit, located near Aberfeldy in the central Scottish Highlands. Microprobe analyses of sphalerite show a wide range in minor element content (0–17 mol. % FeS, 0–3 mol. % MnS), and sphalerites of contrasting composition are often found in the same rock. This suggests that equilibrium domains in some rocks were minute (< 1 mm), during regional metamorphism. Pressures derived from the selective application of the sphalerite geobarometer are consistent with other mineralogical evidence of peak metamorphic pressures in the range 7–10 kbar, at 540–580 °C. However, there is considerable evidence of partial retrograde re-equilibration of sphalerite, by continued buffering with pyrite+ pyrrhotine and by outward diffusion of iron. Marginal depletion of Fe and Mn in sphalerite within coarse carbonate rocks is attributed to partitioning reactions following recrystallization. Sphalerite which has retained its pre-metamorphic composition shows systematic variations in composition through profiles of mineralized beds, which may be related to depositional environments. Bimodal primary compositions can be explained by precipitation of zinc sulphides under the contrasting chemical environments of hydrothermal vents and cooler, exhaled brine layers on the sea floor.

Cesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x) H2O, is hexagonal, space group P63/m, a = 9.446(1) and c = 6.895(1) Å, Z = 2. The crystal structure refinement, carried out by utilizing 457 independent reflections (final R = 0.021), shows that cesanite is isotypic to hydroxyapatite. The P atom of apatite is completely replaced in cesanite by an S atom; the two independent Ca sites of apatite are occupied respectively by Na and Na + Ca, the charge balance being by partial substitution of H2O for OH− although the occupancy of the (H2O,OH−) sites is not complete. The relationship between the water vacancies and the structural features of the (Ca,Na) polyhedron is discussed. A new general formula for the apatite-wilkeite-ellestadite series is proposed.

Electron microprobe analyses of almandine-spessartine garnets from pegmatites and aplites from the Hub Kapong batholith and Phuket Island in peninsular Thailand show three types of zoning. Garnets from pegmatites show extreme zoning, with Mn-rich cores (⋍ 80 % spessartine) and Mn-poor rims (⩾ 40 % spessartine), whereas those from aplites are either unzoned (35–40% spessartine) within the limits of detection, or have Mn-enriched rims (cores 45 %, rims 55 % spessartine). The origin of the three types of zoning is considered to reflect different crystal growth histories in each case. The pegmatitic garnets grew under conditions favourable for the development and preservation of marked concentration gradients—low nucleation density, rapid growth rate and slow cation diffusion rates for the crystal and rapid diffusion rates for the pegmatitic liquid. The aplitic garnets had a more complex growth history, with slower growth rates and faster diffusion rates for the crystal, coupled with slower diffusion rates within the aplite magma, tending to prevent the formation and preservation of concentration gradients. Subsequent resorption of aplitic garnets at lower temperatures gave rise to Mn-rich rims because of the preferential retention of Mn by the garnet; lower cation diffusion rates within the crystal permitted these marginal concentration gradients to be preserved.

The distribution of the minor impurities, aluminium and silicon, between co-existing phases in altered ilmenite grains from three Western Australian localities has been investigated using SEM and electronmicroprobe analyses. A striking dependence of the impurity levels on the Ti/(Ti + Fe) fraction is observed. For compositions with Ti/(Ti + Fe) between 0.45 and 0.60, i.e. between ferrian-ilmenite and pseudorutile, the impurity content is virtually independent of Ti/(Ti + Fe), and is very low (0.2 wt. % Al2O3. 0.05 wt. % SiO2). For compositions between those of rutile and pseudorutile, there is a direct correlation between the impurity contents and the Ti content of the alteration phase. The impurity levels increase with increasing Ti/(Ti+Fe) to about 3 wt. % Al2O3 and 1 wt. % SiO2 for compositions close to TiO2. Thus during the latter stages of ilmenite alteration, alumina and silica are extracted from the ambient environment and are coprecipitated with, or adsorbed on to, the alteration products. The observed dependence of the alumina and silica contents on extent of alteration is consistent with a two-stage alteration mechanism earlier proposed (Grey and Reid, 1975).