During research on the influence of temperature on cation partitioning in natural Mg-Al-Fe2+-Fe3+ spinels, some crystals were accidentally oxidized during heat treatment. The oxidation product, studied by means of single-crystal X-ray diffraction, turned out to be a phase retaining the Fd3m parent spinel structure, but with cell edge a and oxygen coordinate u considerably smaller than the parent ones (a ∼ 8.087 as compared with ∼ 8.111 Å; u ∼ 0.2609 vs. 0.2617–0.2636) and with vacant sites due to oxidation.

Assuming that the oxidation process must occur due to the addition of oxygen to the crystal boundary as cations are being preserved and rising in total valence, the site population was determined and compared with that of untreated and heated samples. It was found that, on oxidation, a charge enrichment in the tetrahedral site T had occurred, this phenomenon following that observed during heating at increasing temperatures also in other spinel series. This continuity was always in the direction of an increase in random charge distribution. Cation vacancies produced during oxidation were restricted to the octahedral site M.

Examination of bulk sections by reflected light microscopy showed a few hematite lamellae as inclusions in the oxidized samples, not detectable by microprobe analysis or single-crystal structural refinement. However, hematite played a marginal part in oxidation. Vacancy-oxygen distances in oxidized spinels were determined from experimental data in the literature.

The crystal structure of mawbyite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is monoclinic, C2/m with a = 9.066(4), b = 6.286(3) c = 7.564(3) Å, β = 114.857(5)°, Z = 2; the structure has been refined to a conventional R = 4.3% using 361 observed reflections [I> 3σ(I)]. The structure contains chains of edgesharing Fe(O,OH)6 octahedra which are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations. Mawbyite is confirmed to be isostructural with tsumcorite and dimorphous with carminite and the relationship between these two structures is discussed.

The FTIR spectra of synthetic BaMg(CO3)2 (norsethite) are measured at ambient temperature and atmospheric pressure, and the influence of formation conditions on the FTIR spectra is investigated. The results are compared with those for natural norsethite from Långban (Sweden) and Rosh Pinah (Namibia). The Raman spectrum of synthetic norsethite is reported, too. A number of first-order internal modes of the carbonate ion group (ν1, ν2, ν3, ν4) are found to be infrared and Raman active. Additonally, the (ν1+ν3) and (ν1+ν4) combination modes and the (2*ν2) overtone are observed in the FTIR and Raman spectrum, respectively. The carbon isotopic-shift coefficient for ν2 due to the substitution of 12C by 13C (ν2(13CO32-)/ν2(12CO32-) = 0.971 ± 0.002), observed by FTIR spectroscopy, agrees with the theoretical value of 0.969.

Two C2/c pyroxene suites from sodic alkaline rocks (Basanite-Phonolite: B-Ph and Alkali basalt-Trachyphonolite: AB-T) belonging to the McMurdo Volcanic Group (Mt. Melbourne province and Mt. Erebus, Antarctica) were investigated by single-crystal X-ray diffraction combined with electron probe microanalysis which together provide accurate site occupancy and site configuration parameters. Variations in site volumes distinguish the clinopyroxenes belonging to the more alkaline B-Ph suite from those of the AB-T suite. The former have higher VM2 and, for similar cell volume, lower VM1 and higher VT. In these C2/c pyroxenes, the bond lengths of M1 depend on R3+ content, necessary to balance AlIV in the T site. M1 geometric variations are similar for both B-Ph and AB-T suites. However, the M2 site is crucial for variations in polyhedral configurations. The increase in AlIV affects the shortest M2-O bond lengths in different ways depending on (Ca+Na) contents in the M2 site. Thus, the clinopyroxenes were distinguished in two different groups not related to the two suites. The first group is characterized by (Ca+Na) higher than 0.90 atoms per formula unit but shows a good positive correlation between the shortest M2-O bond lengths and AlIV content, at quite constant (Ca+Na). The second group has (Ca+Na) less than 0.90 atoms per formula unit but shows a poor correlation between the shortest M2-O bond lengths and AlIV content. In general, shortening of the longest M2-O bond lengths is associated with increase in AlIV. The cell and M1 volumes suggest that the clinopyroxenes, including the larger and sometimes resorbed macrocrysts, crystallized at a pressure lower than 5 kbar, fitting the petrography and evolved character of the rocks in question.

A small 33 ± 0.8 Ma lamproite pluton is exposed in the midst of a 23–26 Ma basalt-rhyolite province in Middle Park, NW Colorado. It contains abundant phlogopite phenocrysts in a fine-grained groundmass of analcime pseudomorphs after leucite, biotite, potassic richterite, apatite, ilmenite and accessory diopside. The phlogopite phenocryst cores contain ∼4 wt.% TiO2, 1% Cr2O3 and 0.2% BaO. The smallest groundmass biotites have normal pleochroism but compositions unlike any previously reported, with ∼2% Al2O3, ∼8% TiO2 and F <1.5%. Apart from those elements affected by leucite alteration, both the elemental and isotopic composition of this lamproite are close to those of the Leucite Hills, Wyoming. Its Nd-isotopic model age (TDM = 1.6 Ga) is outside the Leucite Hills range but within that of other Tertiary strongly potassic magmatism in the region underlain by the Wyoming craton. Evidence from both teleseismic tomography and the mantle xenoliths within other western USA mafic ultrapotassic igneous suites shows that the total lithospheric thickness beneath NW Colorado was probably ∼150–200 km at 33 Ma, when the Middle Park lamproite was emplaced. This is an important constraint on tectonomagmatic models for the Cenozoic evolution of this northernmost part of the Rio Grande rift system.

Alkali-deficient tourmalines are found in albitized rocks from the hanging-wall of the Sullivan Pb-Zn-Ag deposit (British Columbia, Canada). They approximate the Mg-equivalent of foitite with an idealized formula □(Mg2Al)Al6Si6O18(BO3)3(OH)4. Major chemical substitutions in the tourmalines are the alkali-defect type [Na*(x) + Mg*(Y) = □(x) + Al(Y)] and the uvite type [Na*(x) + Al(Y) = Ca(x) + Mg*(Y)], where Na* = Na + K, Mg* = Mg + Fe + Mn. The occurrence of these alkali-deficient tourmalines reflects a unique geochemical environment that is either alkali-depleted overall or one in which the alkalis preferentially partitioned into coexisting minerals (e.g. albite).

Some of the alkali-deficient tourmalines have unusually high Mn contents (up to 1.5 wt.% MnO) compared to other Sullivan tourmalines. Manganese has a strong preference for incorporation into coexisting garnet and carbonate at Sullivan, thus many tourmalines in Mn-rich rocks are poor in Mn (<0.2 wt.% MnO). It appears that the dominant controls over the occurrence of Mn-rich tourmalines at Sullivan are the local availability of Mn and the lack of other coexisting minerals that may preferentially incorporate Mn into their structures.

Sulphosalts in the system CuSbS2-CuBiS2 (chalcostibite-emplectite) form a complete solid solution series. Seven compositions with the general formula Cu(SbxBi1–x)S2 have been synthesized using dry methods at 310°C. All members of the series are orthorhombic (space group Pnma) and show smoothly increasing a and b cell parameters with substitution of Bi for Sb; the c cell parameter increases up to 50% CuBiS2 substitution and then becomes constant. DSC experiments on CuBiS2 show an endothermic heat effect (2.45 kJ/mol.) at 472°C due to the breakdown reaction to Cu3BiS3 (wittichenite) plus Bi2S3 (bismuthinite). With the addition of 10% CuSbS2 to CuBiS2, the decomposition temperature increases and the endothermic peak is broadened but the energy remains essentially the same (2.53 kJ/mol.). No evidence of this decomposition was observed when the amount of the CuSbS2 component was >30%. The local structure and co-ordination of Cu in the samples were studied by EXAFS analysis of the Cu-K edge but no significant variation occurs in the local Cu environment. The Debye-Waller factor for the first shell of S atoms surrounding Cu in end member CuSbS2 tends to be slightly smaller than for the intermediate solid solutions, suggesting that the tetrahedral Cu environments in the intermediate composition samples is somewhat more disordered than in the end-member. The low expansion characteristics along c appear to be controlled by the linkages between the (CuS3 + BiS2) sheets perpendicular to c being relatively inflexible.

Warwickite constitutes about 5% of an outcrop of metamorphosed ultramafic rocks of Precambrian age in North-West Greenland. It occurs as slender grains, several millimetres long, and in anhedral grains up to 5 mm in size, together with forsterite, pleonaste, phlogopite, magnetite ± tourmaline. Post-metamorphic alteration of warwickite produced a network of boron-rich minerals and magnetite. The warwickite, containing up to 9.72% Al2O3, displays a significantly different chemical composition from warwickite elsewhere, such as that in recrystallized limestones from the type locality Warwick, New York, and in lamproitic and carbonatite-like rocks at Jumilla, Spain.

The crystal structure of averievite, Cu5O2(VO4)2·nMX has been determined. Trigonal system, space group P3, a = 6.375(1), c = 8.399(1) Å, V = 295.6(1) Å3, Z = 1, Dx = 4.01(1) g/cm3. The atomic arrangement is characterized by infinite nets parallel to (001) composed of [OCu4]6+ tetrahedra linked via corners in hexagonal rings. The bases of neigbouring tetrahedra are in one plane and their non-shared corners are turned to the opposite sides. The [VO4]3− tetrahedra are attached to the bases of [OCu4] tetrahedra. There are large (R >3.2 Å) channels in the structure where large molecular particles can enter. The comparison of the averievite structure with related compounds (in particular, copper oxovanadates) is given from the point of view of [OT4] polyion crystal chemistry.

Igneous graphite, a rare constituent in terrestrial mafic and ultramafic rocks, occurs in three EH and one EL enstatite chondrite impact-melt breccias as 2–150 µm long euhedral laths, some with pyramidal terminations. In contrast, graphite in most enstatite chondrites exsolved from metallic Fe-Ni as polygonal, rounded or irregular aggregates. Literature data for five EH chondrites on C combusting at high temperatures show that Abee contains the most homogeneous C isotopes (i.e. δ13C = −8.1 ± 2.1‰); in addition, Abee's mean δ13C value is the same as the average high-temperature C value for the set of five EH chondrites. This suggests that Abee scavenged C from a plurality of sources on its parent body and homogenized the C during a large-scale melting event. Whereas igneous graphite in terrestrial rocks typically forms at relatively high pressure and only moderately low oxygen fugacity (e.g., ∼ 5 kbar, logfO2 ∼ −10 at 1200°C), igneous graphite in asteroidal meteorites formed at much lower pressures and oxygen fugacities.

The proton microprobe has been used to determine contents of Ca, Ti, Ni, Mn and Zn in the olivine of 54 spinel lherzolite xenoliths from Australian and Chinese basalts. These data are compared with proton-probe data for Ni, Mn and Zn in the olivine of 180 garnet peridotite xenoliths from African and Siberian kimberlites. Fe, Mn, Ni and Zn contents are well-correlated; because the spinel lherzolite olivines have higher mean Fe contents than garnet peridotite olivines (average Fo89.6vs. Fo90–92) they also have lower Ni and higher Mn contents. Zn and Fe are well-correlated in garnet peridotite olivine, but in spinel peridotites this relationship is perturbed by partitioning of Zn into spinel. None of these elements shows significant correlation with temperature. Consistent differences in trace-element contents of olivines in the two suites is interpreted as reflecting the greater degree of depletion of Archean garnet peridotites as compared to Phanerozoic spinel lherzolites. Ca and Ti contents of spinel-peridotite olivine are well correlated with one another, and with temperature as determined by several types of geothermometer. However, Ca contents are poorly correlated with pressure as determined by the Ca-in-olivine barometer of Köhler and Brey (1990). This reflects the strong T-dependence of this barometer: the uncertainty in pressure (calculated by this method) which is produced by the ±50°C uncertainty expected of any geothermometer is ca ± 8 kbar, corresponding to the entire width of the spinel-lherzolite field at 900–1200°C.

Back-scattered electron imaging with a scanning electron microscope was applied to the intimate association of fine chalcopyrite grains and sphalerite (‘chalcopyrite disease’) in synthesized products and natural specimens, in order to distinguish between diagnostic features of two formation mechanisms: replacement and coprecipitation. In the synthetic chalcopyrite disease in Fe-bearing sphalerite formed by a replacement reaction, chalcopyrite occurs as fine lamellae, which are also observed in relatively Fe-rich growth bands of the natural zoned sphalerite. Ellipsoidal to lens-like habits of chalcopyrite appear in sphalerite that has undergone extensive replacement reactions. These textures may have grown steadily from the lamellar chalcopyrite by consuming the FeS component dissolved in the sphalerite. All the sphalerite samples formed by the coprecipitation mechanism are Fe-poor, hosting triangular or irregularly bleb-like inclusions of chalcopyrite. This variety of chalcopyrite morphology could be attributed to diffusion rates and variations in fluid saturation, and their effect on the rate of crystal growth. Thus, in both replacement and coprecipitation the chalcopyrite habit depends strongly both on the FeS content of the host sphalerite and on kinetic factors, and is significant when interpreting chalcopyrite disease textures in natural samples.

The Las Aguilas Ni-Cu-PGE deposit is associated with a sequence of basic-ultrabasic rocks made up of dunite, harzurgite, norite and amphibolite. These igneous (partially metamorphosed) rocks, and their host granulites, gneisses and migmatites of probable Precambrian age, are highly folded. The sulphide ore, consisting of pyrrhotite, pentlandite and chalcopyrite, occurs in the cores of both antiform and synform structures, within dunite, harzburgite and mainly along shear zones in bronzitite, replacing small mylonitic subgrains. The platinum-group mineral assemblage is dominated by Pd bismuthotellurides (Pt-free merenskyite, palladian bismuthian melonite and michenerite), with minor sperrylite, and PGE-sulpharsenides. The latter often occur as single, zoned crystals frequently showing cores of irarsite; outside these are concentric zones of cobaltian hollingworthite, rhodian nickelian cobaltite and Fe-rich nickelian cobaltite.

Mineralogical, textural and chemical evidence indicate that the sperrylite and platinum-group element sulpharsenides were formed during a primary magmatic event associated with the fractionation of a basaltic melt, which was contaminated by the assimilation of metamorphic crustal rocks. PGE sulpharsenides crystallized from As-bearing, residual magmatic liquids that collected PGE and segregated after the crystallization of the monosulfide solid solution. During high-grade metamorphism, sulpharsenides were remobilized as solid crystals in the liquated sulfides suffering partial dissolution and fracturing. On the other hand, there is no evidence of a primary concentration of Pd-bismuthotelluride minerals, and their present spatial distribution is only the consequence of their formation under high- to medium-grade metamorphism, down to temperatures of below 500°C. Pd bismuthotellurides crystallize even in fractures of sulpharsenides, attached to the boundaries of highly dissolved sulpharsenide crystals, and intergrown with molybdenite.

The textural and paragenetic relationships of sulphide and sulphosalt minerals within Cu-Pb-Sb-Bi hydrothermal vein mineralization at the Apollo mine, Siegerland, Germany, are interpreted in terms of various reaction sequences. An earlier primary sulphide mineralization hosted within a siderite vein of the Siegerland type, with pyrite, chalcopyrite, sphalerite and galena as main component phases, has been overprinted by Sb-, Bi- and Cu-rich fluids. This superposition resulted in the formation of new quartz-stibnite veins, and various mineral reactions with the primary sulphides including the formation of the sulphosalt minerals semseyite, tetrahedrite, meneghinite, jaskolskiite, boulangerite, bournonite and zinkenite. Based on microprobe analyses of reaction pairs and determination of mineral proportions in some cases, a series of quantitative data for each mineral reaction may be generated. This, in turn, allows for the construction of isocon diagrams permitting the relative mobility and immobility of all chemical elements involved in each reaction to be discussed. Two stages of reactive replacement are identified, characterized by immobile behaviour of S and supply of Sb and Cu during the first stage and relative immobility of S and Sb with no further supply of metals during the second stage. Formation of sulphosalts inside the siderite vein during the first stage is interpreted as a decrease of disequilibrium between hydrothermal fluids and pre-existing vein minerals. Replacement processes of the second stage are interpreted as an equilibration of geochemical contrasts between different points within the siderite vein and also between the siderite and quartz-stibnite vein systems. The geochemical evolution of fluid composition during the entire mineralizing event may therefore be modelled, based on the transfer of chemical components reflected in the succession of mineral reactions. Such an approach has applications to comparable polyphase mineralization sequences, in which an understanding of fluid evolution patterns may greatly assist in the development of genetic models for mineral deposits. Solid-state diffusion and grain-boundary diffusion are considered to be the dominant mechanisms for short-range mass transport, whereas diffusion of ionic and complex species through the fluid is considered to be of major importance in long-range mass transport.

A sample of the zeolite paulingite from the locality Vinarická Hora was investigated by means of chemical, thermal, powder and single crystal X-ray methods. The fully transparent, colourless to pale yellow crystals exhibit the form {110} and occur together with phillipsite. The chemical composition is (Ca2.57K2.28Ba1.39Na0.38)(Al11.55Si30.59O84)·27H2O, Z = 16 with minor amounts of Mg (<0.05), Sr (<0.13), Mn (<0.01), and Fe (<0.04). The chemical differences from previously described paulingites are a high Ba-content, a lower Si/(Al+Fe) ratio of 2.64, and a reduced water-content. The calculated density is 2.098 g cm−3, and the observed refractive index is 1.482(2). The dehydration behaviour is characterized by a main weight loss from 24–190°C (−11.2 wt.%, ≅ 21H2O) and a minor weight loss from 190–390°C (−3.1 wt.%, ≅ 6H2O). The rehydration capability was proven up to 150°C. The dehydration process during the main weight loss is accompanied by a reduction of the cell volume of 11%. The refined lattice parameters of the X-ray powder data are a a = 35.1231 (5) Å and a = 33.7485(8) Å of an untreated and a dehydrated sample, respectively. A breakdown of the paulingite structure can be observed while the remaining water content decomposes. The single crystal X-ray refinement of this chemically different sample material derived three main cation positions, which are inside a so called paulingite or π-cage (Ca), between 8-rings of neighbouring π-cages (Ba), and in the centre of the non-planar 8-rings of the γ-cage (K). Further partially occupied cation positions (Ca,Na) were located in the planar 8-rings of the α- and γ-cages. No positions within the double 8-membered rings were detected. The water is localized around the main cation positions and in three clusters of partially occupied sites.

The North Qôroq centre comprises a series of nested nepheline syenite intrusions and forms part of the mid-late Proterozoic Gardar province of South Greenland. Within the centre fractionation has produced varied rock types ranging from augite-syenite to lujavrite, a eudialyte microsyenite. Samples of eudialyte from the lujavrites of unit SN1B of the centre show evidence for two-stage alteration. This alteration ranges from slight modification along crystal margins to complete breakdown and replacement by new pseudomorphing phases. Modification to crystal margins is accompanied by increasing Nb and Zr contents and is related to metasomatism produced by the intrusion of younger syenite units of the North Qôroq centre. More extensive alteration is as a result of metasomatism followed by lower-temperature supergene alteration. Simplified reactions for this breakdown include eudialyte + metasomatic fluid = allanite + nepheline; eudialyte + metasomatic fluid = titanite + aegirine + møsandrite + wöhlerite; eudialyte + fluid = zirfesite + fluid. Mass balance calculations for altered compared with unaltered samples of lujavrite show that alteration took place at approximately constant volume with an overall increase in Fe (+2.41 g/100g), Si and K (+0.65 and +0.61 g/100g), whilst Na (−2.67 g/100g) and all trace elements, particularly La, Y, Nb and Zr (−5.6 to −166 g/10000g) are lost from the system.

Gold in Early Proterozoic Birimian greenstone at Prestea in Ghana is associated with base metal sulphides and sulphosalts including arsenopyrite, pyrite, sphalerite, chalcopyrite, pyrrhotite, galena, tetrahedrite, bournonite, boulangerite and jamesonite. The occurrence of the gold is intimately associated with arsenopyrite and the sulphosalts, and to a lesser extent with the other sulphides. The tetrahedrites at Prestea constitute the major component of sulphosalts associated with gold and occurring in two distinct types. Type I show ideal stoichiometric composition. Type II tetrahedrites deviated from the ideal stoichiometry and are represented approximately by the average formula (Cu,Ag)9.61(Fe,Zn)2.39(Sb,As)4S13. The tetrahedrites co-precipitated with gold exhibit ideal characteristics indicating an equilibruim state of the mineralizing fluid during precipitation. Three types of pyrites were distinguished by electron-microprobe analyses based on their As, Co and Ni composition. The As content in type I vary from 0.15 to 0.37 wt%, and contain up to 2 wt.% Co.Type II pyrites are As-rich and form the most dominant with As content ranging from 0.2 to 2.69 wt.%. Ni content varies from below-detection to 1000 ppm. Type III pyrites are poor in the trace elements and consistent with the stoichiometric composition. The mineralization occurred in three paragenetic stages from at least a two-phase hydrothermal fluid, with stage II forming a prolonged and main stage of the ore and gold mineralization. Redox changes in ore fluid which were triggered by episodic pressure releases during fissuring and fracturing caused fluctuation of the activity of the As/Ni ratio and subsequent oscillatory zoning of Ni in As-rich ores.

A Ba-rich celestine (Sr0.87Ba0.13SO4) filling cavities of volcanoclastic rocks from Montecchio Maggiore (Vicenza, Italy) was studied. The role of the Ba content in the mineral was determined using X-ray powder data, single crystal X-ray refinement, thermal and chemical analyses. The unit cell parameters (obtained by single crystal diffraction) are a = 8.408, b = 5.372, c = 6.897 Å, and the refinement in the space group Pnma (Z = 4) gives the final R value of 0.039. The average (Sr,Ba)-oxygen bond length is 2.842 Å and agrees with an occupancy of Sr 87% and Ba 13%. Individual bond lengths (Sr,Ba)-O and bond strength calculations confirm that all twelve interactions are significant and define an irregular array around the cation.

Jarosite, a hydrous potassium iron sulphate mineral, has been found as the product of weathering in a silicic chalk building stone of a 13th century abbey at Fontevrault (Maine-et-Loire, France). Destabilization of pyrite and glauconite dispersed in the calcareous stone results in the formation of jarosite. The alteration process is probably of very local origin, within the zone in the building stone at its surface where oxidation occurs during wetting and drying on a cyclical basis. The problem of the incompatibility of highly acidic solutions needed to stabilise jarosite (2.5 < pH) within the highly porous, calcareous silicate rock is not explained at present.

Recent studies on albitite rocks located in the granodiorite complex of Central Sardinia have revealed that epidote has a widespread occurrence as a light rare-earth element (LREE)-bearing accessory common phase. Titanite has been recorded as a heavy rare earth element (HREE)-bearing mineral. The Hercynian granodiorite complex of Central Sardinia is composed chiefly of quartz, Ca-plagioclase, K-feldspar and biotite and of a wide variety of secondary assemblages, mainly allanite, titanite and zircon. Albitic plagioclase and quartz are the main mineral components of the albitites. Additional minerals include, besides allanite and epidote, a more calcic-plagioclase (oligoclase), K-feldspar, chlorite, titanite and more rarely muscovite. The mineral assemblages and REE-bearing minerals of albitites were analysed by wavelength dispersive spectrometry (WDS). Chemical data suggest that there is a near complete solid-solution between epidote and allanite whereas little variations in HREE of titanites were detected. In epidote-group minerals a pronounced zoning in REE was observed while titanite was recorded unzoned. Textural relations were studied by SEM to distinguish primary from secondary epidotes. Chemical criteria to recognize magmatic from alteration epidotes were also applied. The alteration epidotes mainly occur and generally originate from plagioclase alteration and from leaching of magmatic allanite. Comparison of textures using both the SEM technique and EPMA data showed that the characteristic ‘patchy zoning’, observed in epidotes, corresponds with different amounts of REE in these minerals.

The schematic model proposed for the epidote-forming reactions during the metasomatic processes that affected the granodiorites involves: (i) the instability of the anorthitic component of plagioclase; (ii) the simultaneous formation of albite; (iii) the leaching of the magmatic allanite with a redistribution of REE in the epidotes of the albitites.