The mineral priderite has been examined by electron microprobe analysis and electron diffraction. The composition was approximately (K0.97Ba0.33)(Fe1.17Ti6.60Mg0.23)O16, which is in line with the observed superlattice periodicity of m = 5.88, there being inter-growths of m = 5 and m = 6 superstructures. A surprisingly high degree of lateral correlation between tunnel cations was noted.

The ultramafic-hosted disseminated nickel sulphide deposit at Mount Keith, Western Australia, originally consisted of sulphide droplets and chrome spinels interstitial to olivine. During cooling, the sulphide droplets crystallized to pentlandite-pyrrhotine. Hydration and carbonation caused rimming and replacement of pentlandite-pyrrhotine by tochilinite, magnetite, and magnesite. These textures are interpreted in terms of diffusion between serpentinite matrix and the sulphide blebs.

Cr micas identified as chrome phengites occur in association with other Cr-rich minerals in a peculiar schist which lies along a complex shear zone within the pre-Caledonian Erris Complex. The schist generally has a chaotic internal structure but locally there is a crude planar mineralogical zoning with a serpentinebearing zone structurally above a Cr mica zone. Chemical analyses indicate that the schist is a tectonic derivative of a mixture of rock with a pronounced metasomatic character.

Six specimens of Australian iron ore, three hematite-rich and three goethite-rich, have been investigated by Mössbauer spectroscopy at both 300 K and 4.2 K. The resulting spectra provide data relevant to crystallite particle size variations in the hematite and goethite, the extent of isomorphous replacement, and the existence within one specimen of a poorly defined goethite-like material.

Sulphide and sulphosalt mineralization in the Hällefors silver mining district occurs as stratabound bodies in skarn-like black carbonates and other carbonates in the eastern part of the district, and as epigenetic, tectonically controlled vein mineralization in tuffaceous metavolcanics and, to a lesser extent in slates, in the western part.

Previous work has suggested that the Ag-bearing Hällefors deposits were formed by the action of metamorphic solutions on sediments of volcano-sedimentary origin. At the stages of sulphosalt and sulphide formation, temperature and pressure conditions were probably in the ranges 500–440 K and 4.5–3.5 kbar. Examination of a log aS2-1/T diagram and of Ag-Sb phase relations combined with study of the ores suggest the paragenesis of the Ag-bearing minerals is as follows: allargentum and dyscrasite as exsolution bodies in silver bearing galena; Ag-containing tetrahedrite → freibergite → miargyrite → pyrargyrite → stephanite (from hydrothermal solutions).

Chemical analyses and structural formulae of biotites from the Zaër pluton, a zoned granitic body in the Central Hercynian Massif of Morocco, are presented. The pluton grades from more mafic single-mica granodioritic facies near the margin to more felsic two-mica granitic facies in the central part. There is a relationship between the composition of the biotites and that of the host rocks. Biotite composition in the internal two-mica facies was influenced by a hydrothermal phase.

The chemistry and crystallography of type georgiadesite from Laurion, Greece, have been reexamined using electron microprobe analysis along with powder and single-crystal X-ray diffraction. Georgiadesite is monoclinic, P21/c, with a = 13.803(10), b = 7.910(2), c = 10.812(4) Å, and β = 102.68(3)°. No twinning was observed. The probable chemical formula is either Pb16(AsO4)4Cl14O2(OH)2 or Pb16(AsO4)4Cl14(OH)6. The calculated densities for these formulae are 6.39 and 6.44 g/cm3, respectively, compared to a measured value of 6.3 + 0.3 g/cm3

Using solution techniques, ΔG°f(298.2k) has been calculated for schröckingerite, NaCa3UO2(CO3)3 SO4F · 10H2O, and grimselite, NaK3UO2(CO3)3 · H2O. The values are −8077.3 ±8.7 and −4051.3 ±1.8 kJ mol−1 respectively. ΔH°f(298.2k) for grimselite is −4359.0 ± 1.8 kJ mol−1. An estimate for ΔG°f of the synthetic compound Na4UO2(CO3)3(s) using previously published equilibria has been made, −3720.0±9.7 kJ mol−1. The results have been used to reconstruct the chemical environments in which these and related compounds can form. Grimselite is only stable at relatively high activities of K(aq)+ and the alkali metal carbonates containing only potassium or sodium ions have not been reported to occur naturally. This is most probably due to their relatively high solubility in water. Schröckingerite can form from solutions which are more than saturated with respect to calcite and fluorite. The close relationship of schröckingerite with gypsum, observed frequently in the field, is evident from synthetic and solution studies.

Massive stratiform and stratabound sulphide bodies in the central Appalachians exhibit a wide variety of metamorphic features which are typical of similar deposits world-wide. The ores occur as lens- to plate-like bodies which are concordant with the enclosing meta-sediments and volcanics and are interpreted as products of Late Precambrian to Early Palaeozoic submarine volcanism. Sulphide mineralization ranges from pyritic to pyrrhotinic bodies with variable, but Zn- and Cu-dominant, base-metal contents. The deposits have been subjected to metamorphism ranging from greenschist to amphibolite grade. The metamorphism has been pervasive and has resulted in thorough recrystallization of most ores and intense deformation of pyrrhotinic ores, but does not appear to have significantly altered original sulphide assemblages. Recrystallization has homogenized most sulphide minerals including pyrite and sphalerite, so that any original compositional zoning is no longer seen. The presence of chalcopyrite has apparently promoted an increase in grain size and has facilitated post-metamorphic retrograde re-equilibration. Consequently, sphalerite geobarometry is not reliable in Cu-bearing assemblages. Pyrrhotines, mostly hexagonal, have re-equilibrated to low temperatures but commonly display pressure twins and kink-banding, apparently due to the late stages of deformation. Characteristic mineralogical changes in the host rocks include changes in the abundance of minerals, changes in the Fe: Mg ratios, and the presence of gahnite.

The infra-red spectrum and X-ray powder pattern of a chemically analysed specimen of leadhillite, a lead carbonate sulphate hydroxide mineral from Leadhills, Scotland, are shown to be different from those in the literature. The IR spectra of several specimens suggest that mutual replacement of SO4, CO3, and OH may occur in this mineral, and it is thought that this might be responsible for the observed variation in X-ray spacings.

Pectolite has been identified, using petrographic, chemical, and X-ray methods, in kimberlites from the De Beers and Dutoitspan Mines, Kimberley, South Africa and the Letseng-La-Terai Mine, Lesotho. It occurs as radiating aggregates of fibrous or acicular crystals not only in the groundmass of certain kimberlites but also in altered xenoliths included within kimberlite. The occurrence of Na-rich minerals in kimberlite is unusual. It is suggested that it can occur as an apparently primary mineral resulting from the incorporation and assimilation of foreign Na-bearing material prior to final consolidation, and/or as a secondary mineral after metasomatic introduction of Na-bearing fluids.

Unit-cell parameters of synthesized members of the crandallite (a = 7.007 Å, c = 16.216 Å)-goyazite (a = 7.013 Å, c = 16.650 Å) series vary linearly with composition between end-members. Most members of the series consist of 0.1 μm platy crystals, but crandallite also contains some larger (1–5 µm) tapered crystals elongated along the c axis.

With increasing Sr substitution the dehydroxylation temperature decreases from c. 475 °C for crandallite to 420 °C at 20 mole % Sr, and then increases to 440 °C for goyazite. Partial dehydroxylation of crandallite is accompanied by contraction of the c unit cell parameter and expansion of a, thereby retaining an unaltered unit cell volume. The much greater sensitivity of c to both Sr substitution and dehydroxylation may be due to the rigidity of continuous sheets of Al(OH)4O2 octahedra which are parallel to the (001) plane in these minerals.

Zoned spherulites in greenalite-siderite-silica rocks of the Emilia-San Valentin lead-zinc deposit, Sierra de Cartagena, SE Spain, show a core of iron-rich talc, (Mgl.8Fel.2)Si4Ol0(OH)2, an intermediate zone of opal-chalcedony, and a rim of minnesotaite, (Fe2.7Mg0.3)Si4Ol0(OH)2. Crystalllization of the spherulites, presumably from undercooled silica sols carrying dissolved Mg and Fe, began with the non-equilibrium precipitation of metastable iron-rich talc; the residual fluids enveloping the growing spherulites became more iron-rich in composition until metastable equilibrium between iron-rich talc and iron-enriched residual liquid impeded the further growth of the iron-rich talc; the spherulites were then overgrown by colloidal silica flocculates and a rim of minnesotaite precipitated from the iron-enriched residual fluid. The proposed crystallization model implies that, if talc and minnesotaite represent an isomorphic series, under equilibrium conditions there is a broad immiscibility region in the series.

Small crystals of babingtonite and rare sphene occur in a coarse-grained aggregate of fluorapophyllite, stilbite, and calcite, infilling a late-stage cavity in granodiorite from Harcourt, Victoria. This is the first reported occurrence of babingtonite in Victoria. The assemblage crystallized from fluids in which Ca and F were significant and under P–T conditions of the order of 0.5 kbar, 100–150°C. Some of the fluorapophyllite has been altered to opaline silica suggesting that the residual solutions were acidic.

A detailed study of pyrite in a number of metamorphosed, stratiform, sediment-hosted Pb-Zn deposits has shown the importance of cataclastic deformation, pressure-solution, and grain growth in the deformation and textural development of pyrite. Primary depositional or early diagenetic microstructures are preserved in pyritic ores deformed or metamorphosed at grades up to mid-upper greenschist facies, whereas at higher temperatures only metablastic or annealed pyrite textures are found. Brittle deformation is found at all metamorphic grades and is favoured by coarse grain-sizes. Pressure-solution is a major deformation mechanism in fine-grained pyritic ores in low-grade metamorphic environments. Grain growth and annealing dominate at higher metamorphic temperatures and are likely to have obliterated any evidence of deformation by dislocation processes. Significant macroscopic ductility of fine-grained pyritic ores in low-grade environments may be accounted for by a combination of pressure-solution, grain boundary sliding, and cataclastic flow.

An unnamed Fe3+ analogue of hematolite is described from Sterling Hill, New Jersey and Långban, Sweden. Eight microprobe analyses are in good agreement with ratios derived from a prior analysis which yielded: Al2O3 0.24, Fe2O3 10.85, MgO 10.61, MnO 41.76, As2O3 6.65, As2O5 15.29, H2O 13.23 (rem. = 1.63), sum = 100.26 %. Single-crystal study indicated that this compound is hexagonal with a = 8.28 Å, but the value of c could not be well-defined due to complex polytypism giving rise to diffuse and poorly resolved reflections along c*. In one case, a value of c = 72.69 Å was dominant. All values that could be determined were multiples of approximately 12 Å. The strongest lines in the X-ray powder diffraction pattern are: 2.400(100), 1.563(100), 6.09(80), 3.42(50), and 5.13(50). This compound is dark red and occurs as platy hexagonal crystals in clusters associated with a wide variety of species in varied assemblages. It remains unnamed because of the ambiguity arising from polytypism.

Sark's Hope silver-lead lode, which was mined during the 1830s and 1840s cuts a Late Precambrian granite at the southernmost point of the island of Sark. The primary ore assemblage is pyrite, galena, chalcopyrite, tennantite, tetrahedrite, sphalerite, marcasite, arsenopyrite, pyrrhotine, bravoite, enargite, and the silver minerals pyrargyrite, pearceite, polybasite, and acanthite. Gangue minerals are hematitic quartz, calcite, and illite. Alteration products include chalcosine, covelline, blaubleibender covelline, limonite, malachite, azurite, cerussite, and anglesite. The generalized paragenesis is of early Fe, Co, Ni, As, and S species and later minerals of Pb, Cu, Ag, Zn, Fe, As, Sb, and S. The earliest alteration products are copper sulphides; these are followed by lead and copper carbonates and sulphates, and hydrated iron and manganese oxides. Growth zoning is a common feature of many of the ore minerals, and electron microprobe analysis shows that this is sometimes related to compositional differences. Tetrahedrite and tennantite, particularly, exhibit a wide range of compositions.