In this work a single crystal of synthetic hercynite, FeAl2O4, was investigated by X-ray diffraction up to 7.5 GPa and at room temperature, in order to determine its pressure–volume equation of state. The unit-cell volume decreases non-linearly with a reduction of 3.4% (i.e. 18.43 Å3). The pressure–volume data were fitted to a third-order Birch-Murnaghan equation of state providing the following coefficients: V0 = 542.58(3)Å3, KT0 = 193.9(1.7) GPa, K' = 6.0(5). These results are consistent with previous investigations of Cr and Al spinels measured with the same experimental approach but the KT0 differs significantly from the experimental determination carried out more than 40 years ago by Wang and Simmons (1972) by the pulse echo overlap method. Our new results were used to redetermine the FeAl2O4(hercynite) = FeO(wüstite) + Al2O3(corundum) equilibrium in P–T space and obtain geobarometric information for Cr-Al spinels found as inclusions in diamond.

The sizes, distributions and shapes of zircon grains within variably deformed granite gneiss from the western Alps have been studied. Zircon shows numerous indicators of a metamorphic response in both the host gneiss and a 5 cm wide continuous ductile shear zone, within which the zircon grain sizes range from <1 urn to >50 μm. However, the very fine grain sizes are virtually absent from grain boundaries. Within this zone, zircons consistently have more rounded and embayed margins, which are interpreted as evidence of dissolution in response to fluid influx during shearing. Zircons are preferentially located near metamorphic muscovite in both the host gneiss and the shear zone and tend to show the poorest crystal shape, indicating that fluids linked to the formation and presence of muscovite may enhance both the crystallization of zircon and its subsequent dissolution. Larger zircon crystals typically show a brittle response to deformation when adjacent to phyllosilicates, with fractures consistently perpendicular to the (001) mica cleavage. The variety of metamorphic behaviour observed for zircon indicates that it may be highly reactive in sub-solidus mid-crustal metamorphic environments.

Natropharmacoalumite, ideally NaAl4[(OH)4(AsO4)3]·4H2O, is a new mineral from the Maria Josefa Gold mine, Rodalquilar, Andalusia region, Spain. It occurs as colourless, intergrown cubic crystals with chenevixite, kaolinite, jarosite and indeterminable mixtures of Fe and Sb oxyhydroxides. Individual crystals are up to 0.5 mm on edge, although crystals are more commonly ˜0.25 mm across and occur in patchy aggregates several millimetres across. The mineral is transparent with a vitreous to adamantine lustre. It is brittle with an imperfect cleavage, irregular fracture and a white streak. The Mohs hardness is ˜2.5 with a calculated densityof 2.56 g cm–3 for the empirical formula. Electron microprobe analyses yielded Na2O 2.52%, K2O 1.49%, Al2O3 29.50%, As2O5 48.84% and H2O was calculated in line with the structural analysis as 16.28% totalling 98.63%. The empirical formula, based upon 20.21 oxygen atoms, is [Na0.57K0.22(H3O)0.21]Σ1.00Al4.05(As2.97O12)(OH)4·4H2O. The five strongest lines in the X-ray powder diffraction pattern are [dobs(Å), Iobs,(hkl)]: 7.759,100,(100); 4.473,40,(111); 3.870,50,(200); 2.446,9,(301); 2.331,12,(311). Natropharmacoalumite is cubic, space group with a = 7.7280(3) Å, V = 461.53(3) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.063 for 295 reflections with F>4σ(F). The structure conforms broadly to that of the general pharmacosiderite structure type, with Na as the dominant cation in cavities of strongly distorted Al octahedra and As tetrahedra. A new group nomenclature system for minerals with the pharmacosiderite structure has been established, including the renaming of aluminopharmacosiderite to pharmacoalumite.

Uvarovite and grossular, the former comparatively rare, occur along the serpentinite-graphite schist contact in the Fengtien area, on the eastern slope of the Central Range of Taiwan. Uvarovite occurs as small emerald-green euhedral crystals on diopside-fels with dodecahedral crystal forms and many other modifications. Its refractive index is 1.782, specific gravity 3.702, and unit cell edge 11.912 Å. Chemical and probe analyses give average Cr2O3 contents of 11.60 wt. %; spectrographic analysis shows significant enrichment in Cr, Be, Co, Y, Sb, and La over grossular. Associated minerals include nephrite, diopside, tremolite asbestos, zoisite, and clinozoisite. Grossular is reddish-brown; large crystals, dodecahedral in form often modified by trapezohedrons, are associated with diopside, idocrase, and calcite. n = 1.746, SG = 3.636, and a = 11.866 Å. Structurally and chemically it is quite near the grossular end member. Grossular is considered to be formed from pneumatolysis associated with the intrusion of ultramafic rocks, whereas uvarovite is a replacement product of relict chromite in the original ultramafic rocks where migration of elements such as silicon and calcium from wall rocks are prominent.

The crystal structure of charoite was investigated mainly by using selected-area electron diffraction (SAED), X-ray diffraction (XRD) and high-resolution electron microscopy (HREM). SAED and XRD patterns indicate that the structure has a monoclinic cell: a = 32.296, b = 19.651, c = 7.16 Å, β = 96.3° and V = 4517 Å3. The space group inferred from systematic absences and HREM images is P21/m. A model of the charoite structure is proposed that is based on the features of related Ca-alkaline silicate structures and HREM images. The structure of charoite consists of three different silicon-oxygen radicals (polymerized SiO4 tetrahedra) which are located between Ca polyhedra. Two of these radicals form continuous tubular structures comprising pectolite-like tetrahedral chains. Calcium polyhedra are joined to form blocks, each of which consists of four columns sharing edges and apices. Potassium and H2O molecules are probably located inside the tubular silicate radicals. From these results, a general formula is derived: K6-7(Ca,Na)18[(Si6O17)(Si12O30)(Si18O45)](OH,F)2.nH2O with two formula units in the unit cell (Z = 2).

Magnetite is present in most carbonatites, and in the most abundant and best-known form of carbonatite, coarse-grained intrusions, it typically falls in a narrow composition range close to Fe3O4. A fine-grained carbonatite from Zambia contains magnetites with an extraordinary array of compositions (from 18–1% TiO2, 10–2% Al2O3, and 16–4% MgO) outranging previously-reported examples. Zoning trends are from high TiO2 to high Al2O3 and MgO. No signs of exsolution are seen. Checks on similar rocks from Germany, Uganda and Tanzania reveal magnetites with comparable compositions, ranges, and zoning. Magnetites from alkaline and alkaline ultramafic silicate volcanic rocks cover only parts of this array. Magnetite analyses from some other fine-grained carbonatites, reported in the literature, fall in the same composition field, suggesting that this form of carbonatite may be distinctive. The chemistry and zoning would be consonant with rapid high-temperature crystallization in the carbonatite melts, with the lack of exsolution pointing to fast quenching: this contrasts with coarse-grained intrusive carbonatites, in which the magnetite compositions are attributed to slow cooling, with final equilibration at low temperature. In some complexes, both forms of carbonatite, with their different magnetite compositions, are represented.

Chromites from two horizons of the Sukinda area (India) marked as ‘grey ore’ and ‘brown ore’ zones have been studied by 57Fe Mössbauer spectroscopy, which revealed that both chromite types are oxidised and have a type of disordered spinel structure in which octahedral sites are occupied by Fe2+ ions.

The spectra of the grey ore sample can be fitted to three doublets corresponding to Fe2+ (A), Fe3+ (A) and Fe2+ (B) sites. This sample is less oxidised than the brown ore, in which progressive oxidation in the magmatic (?) stage led to the complete conversion of Fe2+ in A sites to Fe3+. The spectra of the brown ore are characterised by two doublets correpsonding to two tetrahedral (A) sites of Fe3+ with different next-nearest neighbour configurations and a third doublet for Fe2+ at the B site. The brown ores have higher chromium and Fe3+ content and have lesser amounts of Ni and Al in comparison to the grey ores. Megascopically, the former shows larger crystal sizes. The high Fe3+ content in the brown ore suggests that this type of chromite was formed in a region of high ƒO2 in the magmatic environment. This perhaps occurred at the part of the mantle where the temperature was higher and the rate of cooling was slower than that of the grey ores which crystallised in the magmatic melt.

Verbeekite, ideally PdSe2, monoclinic with space-group choices C2/m, C2 or Cm; a = 6.659(7), b = 4.124(5), c = 4.438(6) Å, ß = 92.76(3)°, V = 121.7(4) Å3; a:b:c = 1.6147:1:1.0761, Z = 2, is a new, very rare, primary mineral, intimately associated with secondary oosterboschite {(Pd,Cu)7Se5}, from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo. Additional associated minerals are Cu- and Pd-bearing trogtalite {(Co,Cu,Pd)Se2}, Se-bearing digenite and Se-bearing covellite. The strongest five lines of the X-ray powder-diffraction pattern {d in Å (I) (hkl)} are: 4.423(30)(001), 3.496 (30)(110), 2.718(100)(111), 1.955(50)(310 and 1.896(50)(12). The mineral has also been identified, as a single anhedral 25 µm-sized grain, from Hope's Nose, Torquay, Devon, England where it is associated with native gold, chrisstanleyite Ag2Pd3Se4, oosterboschite(?), unnamed Pd2HgSe3 and cerussite. At Musonoi, altered verbeekite grains do not exceed 200 µm in size and are anhedral, black, with a black streak and a metallic lustre. The mineral is opaque, brittle, has an uneven fracture, and lacks discernible cleavage. The VHN5 ranges 490–610, mean 550 kp/mm2 (2 indentations), roughly approximating a Mohs' hardness of 5Ý. Dcalc. = 7.211 g/cm3 for the ideal formula. Electron-microprobe analyses (mean of 4 spot analyses) yielded Pd 39.6, Cu 0.5, Se 58.8, total 98.9 wt.%. The empirical formula is (Pd0.99Cu0.02)σ1.01Se1.99, based on Pd+Cu+Se = 3. In plane-polarized reflected light, the mineral is a nondescript grey and is neither pleochroic nor perceptibly bireflectant. Anisotropy is moderate with rotation tints in varying shades of brown. Reflectance spectra and colour values are tabulated. The name honours Dr Théodore Verbeek (1927–1991) who was the first geoscientist to study the Musonoi palladium mineralization in the Democratic Republic of Congo (1955–1967) and who co-discovered this new mineral phase.

The exhumation history of mountain belts can be derived from radiometric dating of detrital mineral grains in proximal and distal post- and synorogenic sediments. The application of single-crystal dating techniques avoids the averaging effect that characterizes multi-grain and whole-rock techniques and allows the identification of populations of grains with distinct thermal histories. Of the major single crystal dating methods available, 40Ar/39Ar dating of detrital K-bearing minerals, in particular white mica, is perhaps the most versatile and widely applied technique. For a closure temperature of Ar of 350–400°C, muscovite 40Ar/39Ar ages record the time a rock mass passed through 8–10 km beneath actively eroding mountain belts. Detrital muscovit ages eroded from orogenic mountain belts have been used extensively to identify the provenance of sediments from source regions with distinct thermal histories, determine the history and rate of exhumation of the source region, and provide an upper limit on the sediment age. Here I review the principles of 40Ar/39Ar dating of detrital muscovite and illustrate the method with examples showing how the provenance and the thermal history of sediment source regions derived from such studies can be used to constrain the exhumation and tectonic history of orogenic belts.

Zincalstibite-9R, a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9R is uniaxial (–), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn1.092+Cu0.872+Al0.04)Σ2.00Al1.01(Sb0.975+Si0.02)Σ0.99(OH)12, and the ideal formula is (Zn,Cu)2Al(OH)6[Sb(OH)6]. Zincalstibite-9R crystallizes in space group R, with a = 5.340(2), c = 88.01(2) Å, V = 2173.70(15) Å3 and Z = 9. The crystal structure was refined to R1 = 0.0931 for 370 unique reflections [Fo > 4σ(F)] and R1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date.

The elemental compositions of zoned alkali feldspar megacrysts from the Karkonosze pluton have been analysed and Pb isotope ratios determined using LA-ICP-MS, EMPA and TIMS. The results are used to interpret the magmatic environments within which they crystallized. Growth zones in the megacrysts show fluctuating trace element patterns that reflect a systematic relationship between incompatible LREE and compatible Ba. Chemical gradients between zones in the cores and rims of the megacrysts are not accompanied by significant variation in initial Pb isotope composition. The nucleation and crystallization of the megacrysts is interpreted as having occurred in an environment of magmatic hybridization caused by mixing of mantle and crustal components in which effective homogenization of the Pb isotope composition preceded the onset of megacryst growth. The concentrations of LREE in alkali feldspar zones were used to reconstruct hypothetical melt compositions. Some of the zones appear to have crystallized in an homogenous magmatic environment having clear geochemical affinities with end-member magmas in the Karkonosze pluton, whereas others crystallized in heterogeneous domains of magma hybridization. With the exception of Nd, zones crystallized in more homogeneous magma show LREE fractionation under near-equilibrium conditions. Trace element abundances of megacrysts grown in dynamic, homogeneous magmatic environments of the Karkonosze pluton occasionally deviate from the predicted patterns and show LREE impoverishment.

Grandidierite has been identified in two aluminous metasedimentary xenoliths from quartz-latitic volcanic rocks from Mt. Amiata and Mt. Cimino, central Italy. Physical and electron microprobe data for the grandidierites and petrological data for the grandidierite-bearing xenoliths are presented. The grandidierites formed by a reaction involving pre-existing aluminium rich minerals, possibly at temperatures of at least 800 °C and at low pressures. The grandidierite from Mt. Amiata replaces sillimanite. Several common characteristics can be demonstrated for magmatic and metamorphic grandidierite-bearing rocks. It is suggested that metamorphic rocks in which grandidierite occurs have often undergone partial melting.

Correlated data prove the approximate constancy of the number of oxygen atoms in the unit cells of several nepheline and elaeolite specimens. Thence the number of atoms of each kind per unit cell have been counted. The cell-volumes and optical properties have slso been correlated with the chemical composition. An approximate structure is suggested which, together with the chemical work, explains the variable composition of nepheline. The contents of the unit cell may be written Si16−nAln(Na,K,½Ca)n where n ranges from 6.6 to 8.2. Kaliophilite is shown to possess a much larger cell than that of nepheline, and its Lauegram exhibits higher symmetry. 'Pseudonepheline' (rich in potassium) has a slightly greater cell-volume than normal nepheline, but its Lauegram is almost identical and its axial ratio only slightly less.

Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy data demonstrating that sulfur is accommodated predominantly in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the X-ray photoelectron spectra, however, also indicate that more complex substitution mechanisms incorporating S2– and S4+ are possible. Incorporation of S6+ through clino-anhydrite-type substitution results in an excess of M2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH– for O2–. However, Raman data show no indication of OH–, and instead we suggest charge imbalance is accommodated through F– substituting for O2–. The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements, Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolution–precipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.

Two palladium arsenide-antimonides have been found as small inclusions associated with native gold at Hope's Nose. One of the minerals has been identified as isomertieite; the other is chemically very similar to mertieite-II (Cabri et al., 1975). Electron probe microanalysis gives the formula of the isomertieite as (Pd10.89 Au0.08Cu0.03)Σ11.00(Sb2.01As1.99)Σ4.00 and of mertieite II as (Pd7.90Au0.07Cu0.01)Σ7.98(Sb2.43As0.59)Σ3.02. The relectance spectra of isomertieite in air and in oil at intervals of 10 nm from 400–700 nm are tabulated. The luminance values of the Hope's Nose isomertieite are 55.5 % in air and 42.5% in oil. The type specimen of isomertieite from Itabira, Minas Gerais, Brazil, has been re-examined; a new electron probe analysis is given and improved reflectance spectra are tabulated. The latter gives luminance values of 54.3% in air and 41.3% in oil.

Laumontite is a common zeolite mineral indicative of low-grade metamorphism of lavas and volcaniclastic sediments. Stoichiometric laumontite (CaAl2Si4O12·4.5H2O) dehydrates in air at 298.15 K, 1 bar to leonhardite (CaAl2Si4O12·3.5H2O) via loss of water from the W1 crystallographic site. Consideration of reported X-ray diffraction and calorimetric data indicates that the standard molal volume and entropy for dehydration of laumontite to leonhardite + liquid water are ∼13 cc/mol and ∼8 cal/molK, respectively, at 298.15 K, 1 bar. Equilibrium between laumontite and leonhardite occurs at 70 to 80% relative humidity at 298.15 K, 1 bar, corresponding to a standard molal Gibbs energy and enthalpy of reaction of ∼170±40 and ∼2630±100 cal/mol, respectively. Calculated univariant equilibrium for this reaction is nearly linear from 46±3°C at 1 bar to 235±3°C at 5000 bar. Comparison of geological observations with these results suggests that laumontite forms as ‘leonhardite’ during metamorphism and diagenesis. Consideration of ‘leonhardite’, instead of laumontite, in low-grade metamorphic phase relations facilitates prediction of the relative stabilities of zeolites in natural and geologic systems, where calculated entropies of reaction incorrectly predict that assemblages bearing fully hydrated laumontite are stable at lower temperatures than the zeolites heulandite and stilbite.

Sediments from DSDP 424, a core taken in a hydrothermal mound in the Galapagos Mounds Field, comprise biogenic oozes, siliceous ash-rich layers and two varieties of hydrothermal precipitates, an Fe-rich clay (nontronite), and Mn oxides. Compositionally, these sediments differ considerably from one another and vary in proportion down the core to basement. Geochemical partition studies on the sediments have indicated a variable fractionation of the elements that they contain between clays, carbonate, and Mn oxides with the hydrothermal phases being strongly depleted in trace elements. The hydrothermal sediments are thought to have been formed as a result of the fractional precipitation of Fe silicates and Mn oxides from ascending hydrothermal solutions which are depleted in trace elements due to subsurface precipitation of sulphides, and have had insufficient time to scavenge trace metals from sea water due to their rapid precipitation.

Around the world large quantities of sludge wastes derived from nuclear energy production are currently kept in storage facilities. In the UK, the British government has marked sludge removal as a top priority as these facilities are nearing the end of their operational lifetimes. Therefore chemical understanding of uranium uptake in Mg-rich sludge is critical for successful remediation strategies. Previous studies have explored uranium uptake by the calcium carbonate minerals, calcite and aragonite, under conditions applicable to both natural and anthropogenically perturbed systems. However, studies of the uptake by Mg-rich minerals such as brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite [Mg5(CO3)4 (OH)2·4H2O], have not been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. Experiments with mineral powders were used to determine the partition coefficients (Kd) and coordination of UO22+ during adsorption and co-precipitation with brucite, nesquehonite and hydromagnesite. The Kd values for the selected Mg-rich minerals were comparable or greater than those published for calcium carbonates. Extended X-ray absorption fine structure analysis results showed that the structure of the uranyl-triscarbonato [UO2(CO3)3] species was maintained after surface attachment and that uptake of uranyl ions took place mainly via mineral surface reactions.

The equation of state of Fo90 hydrous ringwoodite has been measured using X-ray powder diffraction to 45 GPa at the GSECARS beam line at the Advanced Photon Source synchrotron at Argonne National Laboratory. The sample was synthesized at 1400°C and 20 GPa in the 5000 ton multi anvil press at Bayerisches Geoinstitut in Bayreuth. The sample has the formula Mg1.70Fe0.192+ Fe0.023+H0.13- Si1.00O4 as determined by electron microprobe, Fourier transform infrared and Mössbauer spectroscopies, and contains ~0.79% H2O by weight. Compression of the sample had been been measured previously to 11 GPa by single crystal X-ray diffraction. A third-order Birch-Murnaghan equation of state fit to all of the data gives V0 = 530.49±0.07 Å3, K0 = 174.6±2.7 GPa and K' = 6.2±0.6. The effect of 1% H incorporation in the structure on the bulk modulus is large and roughly equivalent to an increase in the temperature of ∼600°C at low pressure. The large value of K' indicates significant stiffening of the sample with pressure so that the effect of hydration decreases with pressure.

Chemical, optical, and X-ray data are presented for forsteritic olivine, bronzite-enstatite, diopsidic augite, anorthite, and spinel from ultramafic nodules at seven localities in Auckland province. Olivine has a composition range from Fo79–93 for large primary crystals to Fo80–100 for smaller interstitial grains. Orthopyroxenes (En83–96) carry exsolution lamellae of clinopyroxene parallel to (100); clinopyroxenes are mainly diopsidic augites with exsolved bronzite. The plagioclase (An97) has high-temperature characteristics and a lattice structure probably transitional between primitive and body-centred anorthite. Spinels include chromite, picotite, ceylonite, hercynite, and magnetite. Element distribution indicates that the ultramafic assemblages attained equilibrium at temperatures near 1250 °C and at moderate pressures, corresponding to the melting interval of anhydrous basaltic magmas within the uppermost mantle.