The previously unknown, complex crystal structures of two fibrous ferric iron phosphate minerals have been solved using single-crystal X-ray diffraction data. The structure of a slightly arsenatian kidwellite has been refined in space group P2/c (a = 20.117(4), b = 5.185(1), c = 13.978(3)Å, β = 107.07(3)°, V = 1393.8(5)Å3, Z = 2) to R1 = 5.21%; a revision of both space group symmetry and chemical formula is proposed. The idealized formula is Na(Fe3+,M)9+x(OH)11(H2O)3(PO4)6, where M = Fe3+, Cu2+ or other metal cation, and x ≈ 0.3. The structure of a slightly arsenatian ‘laubmannite’ (as defined by Moore, 1970) has been refined in space group Pbcm (a = 5.172(1), b = 13.999(3), c = 31.083(6)Å, V = 2250.5(8)Å3, Z = 4) to R1 = 3.14%. The revised, idealized formula is (Fe3+,Fe2+,M)8+x(OH,H2O)9(-H2O)2(PO4)5, where M = Fe3+, Cu2+ or other metal cation, and x ≈ 0.1. The framework structures of both minerals are similar. Dominant building units are dimers composed of face- and edge-sharing FeO6 octahedra. Whereas kidwellite contains an additional trimer built of three corner-sharing FeO6 octahedra, ‘laubmannite’ instead contains a dimer built of two corner-sharing FeO6 octahedra. Kidwellite contains only trivalent iron, while one of the Fe sites in ‘laubmannite’ is occupied by a mixture of Fe3+ and Fe2+ in a 1:1 ratio. In both structures, the FeO6-based building units are linked via corners to PO4 tetrahedra; the M sites are located in narrow channels and have very low occupancies (~2 to 7%) and strongly distorted [6]- or [5+1]-coordinations. Close structural relations between kidwellite and ‘laubmannite’, and other fibrous iron phosphates explain observations of epitaxial intergrowths of them.

We examined grains of the platinum-group mineral, laurite (RuS2), from the type locality, Pontyn River, Tanah Laut, Borneo, and from the Tambanio River, southeast Borneo. The grains show a variety of morphologies, including euhedral grains with conchoidal fractures and pits, and spherical grains with no crystal faces, probably because of abrasion. Inclusions are rare, but one grain contains Ca-Al amphibole inclusions, and another contains an inclusion of chalcopyrite+bornite+pentlandite+heazlewoodite (Ni3S2) that is considered to have formed by a two-stage process of exsolution and crystallization from a once homogeneous Fe-Cu-Ni sulphide melt.

All grains examined are solid solutions of Ru and Os with Ir (2.71 –11.76 wt.%) and Pd (0.31–0.66 wt.%). Their compositions are similar to laurite from ophiolitic rocks. The compositions show broad negative correlations between Os and Ir, between As and Ir, and between As (0.4 –0.74 wt.%) and Se (140 to 240 ppm). Laurite with higher Os contains more Se and less Ir and As. The negative correlations between Se and As may be attributed to their occupancy of the S site, but the compositional variations of Os, Ir and As probably reflect the compositional variation of rocks where the crystals grew.

Ratios of S/Se in laurite show a narrow spread from 1380 to 2300, which are similar to ratios for sulphides from the refractory sub-arc mantle. Sulphur isotopic compositions of laurite are independent of chemical compositions and morphologies and are similar to the chondritic value of 0%. The data suggest that S in laurite has not undergone redox changes and originated from the refractory mantle. The data support the formation of laurite in the residual mantle or in a magma generated from such a refractory mantle, followed by erosion after the obduction of the host ultramafic rocks.

Mineral compositions of small peridotite bodies in an Ordovician collision zone of the Vermont Appalachians provide important clues to their tectonic environment of origin. The bodies have been deformed and partially serpentinized under greenschist- to lower amphibolite-facies conditions during the Ordovician and Devonian. Before serpentinization, the peridotite bodies were dunite as shown by their mineral assemblage and by their high MgO, and low Ti and Al whole-rock contents. Despite deformation and metamorphism, remnant olivine and spinel grains occur; their compositions are taken to represent conditions prior to regional metamorphic events. High Mg/(Mg+Fe) in olivine and very high Cr/(Cr+Al) in spinel indicate that the peridotites formed as highly-depleted mantle residues. The compositions are similar to those in harzburgite and dunite from some ophiolites and from fore-arc regions of subduction zones. Accordingly, the southern Vermont peridotites probably formed in a forearc, supra-subduction zone during the Early Palaeozoic. They were subsequently emplaced by obduction of the upper plate of an east-facing subduction complex.

A reappraisal of Hermann's ‘irite’, described in 1836 and 1841, has been attempted by examining and analysing three museum samples, accessioned before 1865. The three samples were determined to be mixtures of chromite, native Os and Ir, rutheniridosmine, platinum, laurite, hongshiite, irarsite, cuprorhodsite, iridsite, prassoite, hollingworthite, erlichmannite, several Ru-Ir-Pt-Ti-Cr-Fe oxide/ hydroxide compounds (sometimes well crystallized), Pt-Ir-K chlorocompounds, and Pt-Ir-Ru-K-Clcontaining opal. The latter two are considered as artifacts generated by the hydrometallurgical processes applied to the crude platinum ores. Individual particles of native iridium and osmium display baroque crystal habits (filaments, leafs, blades, hollow crystals) that could be their natural, although rarely observed, states. There is still doubt about the origin (either natural or artificial) of all Ru-Ir-Pt- Ti-Cr-Fe oxides, but they can be compared with those found in several pristine placer and hard-rock deposits worldwide and in the Urals.

Orthorhombic edingtonite has been found coexisting with tetragonal edingtonite in a specimen from Ice River, British Columbia, Canada.

We report data on the composition and crystal structure of the orthorhombic sample. Lattice parameters are: a = 9.5341(6), b = 9.6446(6), c = 6.5108(7)Å, V = 598.68(8)Å 3. The crystal structure was refined in space group P 21212 to R1 = 1.8% using 879 observed reflections. For the first time, evidence for splitting of the extra-framework Ba site in two different sites (Ba1, Ba2), ~0.37 Å apart, is demonstrated. A comparison with the published crystal structures of tetragonal and orthorhombic edingtonite is made.

The present result supports the suggestion that the two edingtonite phases are a consequence of different nucleation phenomena and not different physicochemical conditions.

Ammonioleucite, (NH4)[AlSi2O6], and its deuterated analogue ND4-ammonioleucite (ND4)[AlSi2O6] have been synthesized in 20–150 mg amounts at 300°C and 500 MPa in 5 mm wide, 4 cm long Au capsules using Rene’ metal hydrothermal autoclaves. The resultant product consists of 20–30 mm-size single tetragonal crystals as well as 50 –100 mm wide clumps of ingrown crystals. Infrared (IR) spectra obtained from powdered samples are assigned on the basis of Td symmetry for both the ammonium and deutero-ammoniumion. They show triply degenerate vibrational bands (i.e. v3 and v4), some overtones, and combination modes from NH4+ and ND4+. While Td symmetry for NH4+ in ammonioleucite is not strictly correct due to distortion of the NH+4 molecule, the non-cubic field is not large enough at room temperature to cause a substantial splitting in the bands. However, this perturbation is documented in the IR spectra by a substantial increase in the FWHH as well as the occurrence of shoulders on the broadened bands. In contrast, at lower temperatures, the observed band splittings in the former triply degenerated states of v3 and v4 could be explained by an effective local field with D2 symmetry.

Rietveld refinement indicates that ammonioleucite, like leucite, has a tetragonal structure with space group symmetry I41/a. Here the NH4+ molecule replaces the K+ cation on the 8-fold co-ordinated W site, which has m symmetry. Substitution of NH4+ for K+ in the leucite structure results in an increase of the cell parameter a, whereas c is slightly reduced. The mean <W–O> bond length of ammonioleucite is increased in comparison to leucite from 3.00 to 3.12 Å whereas the mean <T–O> bond length of 1.65 Å remains unchanged. This results in an increase in the volume of the polyhedron hosting the NH4+ molecule as well as a decrease in distortion for structural channels parallel to the <111> direction, formed by the arrangement of the six-fold rings, on which the W cations are located. The same effect is also observed, in general, when Rb+ or Cs+ is substituted for K+ in leucite.

Arsenic-rich magmatic sulphide mineralization is hosted by a diorite intrusion at Talnotry, southwest Scotland. A relatively abundant and diverse platinum-group mineral assemblage is present and is dominated by sperrylite, irarsite and electrum with subordinate merenskyite, michenerite and froodite. Early euhedral gersdorffite is enriched with respect to Rh, Ir and Pt and in some cases contains exsolved blebs of irarsite or euhedral grains of sperrylite. Sperrylite is also enclosed within silicates and sulphides indicating that it crystallized directly from an As-rich sulphide liquid. Pyrrhotite-chalcopyrite mineral assemblages are consistent with the fractional crystallization of monosulphide solid solution and are overlain by PGE-, Ni- and As-rich mineral assemblages indicative of crystallization from a NiAs liquid. Late-stage, cross-cutting, electrum-bearing chalcopyrite veins are consistent with the crystallization of Cu- and Au-rich intermediate solid solution. The chemistry, mineralogy and lithological relationships of the diorite suggest that it may be an appinite and as such is potentially analogous to the Au-rich lamprophyre dykes present within southwest Scotland.

Silica sinter masses in the southern portion of the Pliocene Puhipuhi geothermal field of Northland, New Zealand, have recrystallized to microcrystalline quartz and moganite but many primary depositional fabrics of the sinters can still be recognized. Finely disseminated cinnabar, acicular stibnite, pyrite framboids and minor livingstonite are distributed through both massive sinter and stromatolitic fabrics with sulphide mineralization extending from fractured rocks about former spring vents into less disturbed sinter layers. The deposition of sulphides in the sinters is part of a continuum of mineralization resulting from the former hydrothermal regime and which extends to depth in the extinct geothermal system. Periodic changes in the hydrology, such as repeated fracturing following fracture sealing facilitated episodic sulphide deposition. Mercury is considered to have travelled in the liquid phase with antimony and precipitated directly as cinnabar. Remobilization of the sulphides, along with the recrystallization of the sinter masses, have produced complex textural relations. The multifaceted paragenesis of the sulphides is reflected in the range of their minor and trace element compositions revealed by electron microprobe analyses.