Crystals of lutetium disilicate (Lu2Si2O7) have been synthesized at 4 GPa and 1200 degrees C, using a piston-cylinder type high-pressure apparatus. Systematic single-crystal X-ray structure analysis shows that Lu2Si2O7, type X is enantiomorphic in space groups P4(1)2(1)2 (structure 1) and P4(3)2(1)2 (structure 2). Unit cell parameters are a = 6.5620(2), c = 11.9535(4) angstrom (1, space group P4(1)2(1)2) and a = 6.5621(9), c = 11.954(2) angstrom (2, space group P4(3)2(1)2), respectively. The crystal structures of the two enantiomers are based on helical chains of Lu cations linked by [Si2O7](6-) groups, which are parallel to each other and possess the same chirality, being right-handed for structure 1 and left-handed for structure 2. More interesting is that we have directly observed the helical chain under high-resolution transmission electron microscopy (HRTEM).

We have conducted electron microprobe (EMP) analysis of 158 grains of platinum-group minerals (PGM; 0.1–1 mm in size) from 11 placer samples collected from Holocene fluvial placers and buried paleochannel placers at various localities in British Columbia. These grains principally comprise Pt-Fe-(Cu) alloy minerals: Fe-rich platinum [ΣPGE:(Fe + Cu + Ni) = 3.6–7.6], Pt3Fe-type alloy (isoferroplatinum or Fe-rich platinum), subordinate “Pt2Fe”-type alloy (probably, a compositional variant of Fe-rich platinum) and the tulameenite-tetraferroplatinum series. Less-abundant are iridium [Ir-dominant Ir-Os-(Pt) alloy] and osmium [Os-dominant Os-Ir-(Pt) alloy]. Ruthenium [Ru-dominant Ru-Ir-Os alloy] occurs as a single grain. One of these Pt-Fe alloy grains is unusually zoned; its core zone is: Pt74.0Fe20.4Cu1.9Ir1.5Rh1.1Pd1.0Os0.08Ru0.01Ni0.01 (in at%) [ΣPGE:(Fe + Cu + Ni) = 3.5], and its rim zone is: Pt78.5Fe15.5Cu1.7Ir1.5Rh1.4 Pd1.2Ni0.15Os0.06Ru<0.01 [ΣPGE:(Fe + Cu + Ni) = 4.8]. This zoning indicates late-stage removal of Fe and corresponding addition of Pt, probably as a result of interaction with a late fluid phase. Various combinations of minor elements: Ir-Rh, Rh-Pd, and Ir-Rh-Pd are observed in the analysed Pt-Fe-Cu alloys. However, the Ir-Pd pair appears to be prohibited because of crystallochemical factors. Minute PGM inclusions in Pt-Fe alloy grains, likely derived from the Tulameen complex, comprise: hongshiite (Pt1.04Pd0.02 Cu0.93), sperrylite (Pt0.93Ir0.03)Σ0.96(As2.02Sb0.01)Σ2.03, hollingworthite-platarsite (Rh0.74 Pt0.21Fe0.02Pd0.02Ir0.01)Σ1.00S0.91As1.10, cuprorhodsite-malanite (Cu0.91Fe0.03Ni<0.01)Σ0.95 (Rh1.06Pt0.89Ir<0.01)Σ1.95S4.10, a rare Te-rich isomertieite (Pd10.96Fe0.03)Σ10.99(Sb1.13 Te0.94)Σ2.07As1.93, and an unusual Pt-Pd-Rh antimonide [(Pt + Pd + Rh):(Sb + As) = 1.2–1.25], related to genkinite. This antimonide may exhibit a minor solid solution extending from genkinite toward stumpflite. In addition, 20 grains of diopside [Ca46.4–49.1Mg42.8–48.2Fe3.1–8.1; ≤0.59 wt% Cr2O3] and 20 grains of olivine [Fo86.8–91.5 Fa7.9–12.5], from a PGM-bearing placer located in the vicinity of the Tulameen complex, were analysed. The compositional ranges of these placer silicates are comparable to those of clinopyroxene and olivine in the olivine clinopyroxenite and dunite units of the Tulameen complex. The majority of the analysed placer PGM grains were probably derived from Alaskan-type source rocks, whereas an ophiolitic source, associated with the Atlin ophiolite complex, is suggested for the placer PGM deposits in the Atlin area, northern British Columbia.

Single crystals of gadolinium holmium silicate hydroxyapatite Gd4.33Ho4.33(SiO4)(6)(OH)(2) have been synthesized at 2.0 GPa and 1450 degrees C using a piston-cylinder-type high-pressure apparatus. The crystal symmetry by single-crystal X-ray diffraction analysis is hexagonal, space group P6(3)/m (No. 176), with a = 9.3142(5) angstrom, C = 6.7010(4) angstrom, Z = 1. Gadolinium and Ho are disordered over the two large cation positions, A(1) and A(2), and charge balance in this silicate apatite is maintained by cation vacancies in A(l). Two other apatite-structure crystals investigated have P (3) over bar and Imma symmetry, and represent either partially ordered Gd-Ho distributions or crystal strain induced during quenching. (C) 2006 Elsevier Inc. All rights reserved.

A series of titanium silicate glasses along the composition joins SiO 2 –TiO 2 , Na 2 SiO 3 –TiO 2 , K 2 SiO 3 –TiO 2 , and CaSiO 3 –TiO 2 have been examined using titanium (Ti) L -edge X-ray absorption near-edge spectroscopy (XANES). XANES spectra were collected at the Canadian Synchrotron Radiation Facility (CSRF), University of Wisconsin, Madison, using the Spherical Grating Monochromator (SGM) beamline. Glass spectra were compared with spectra obtained from crystalline analogues with differing Ti coordination environments: β r Ba 2 TiO 4 ( [4] Ti); fresnoite ( [5] Ti); and rutile and anatase ( [6] Ti). The Ti L -edge data indicate that for homogeneous TiO 2 –SiO 2 glasses Ti coordination is [5] Ti at TiO 2 contents below 3.6 wt% but predominantly [4] Ti with some [5] Ti present above this content. There is no evidence for [6] Ti. For the Na 2 O-containing glasses the L -edge data indicate that Ti is [4] Ti with some [5] Ti at low TiO 2 contents, becomes a mix of [4] Ti and [5] Ti with increasing TiO 2 content, but is exclusively [5] Ti by 14.3 wt% TiO 2 . The K 2 O composition glasses exhibit similar behavior but contain a greater proportion of [4] Ti and less [5] Ti than the equivalent Na 2 O-bearing glasses. These findings are consistent with previous Raman and XANES pre-edge studies. Alkaline-earth-containing glasses behave somewhat differently, with [5] Ti occurring in low TiO 2 content glasses, becoming a mix of [4] Ti and [5] Ti, and then gradually changing to predominantly [4] Ti at higher TiO 2 compositions. Finally, we have obtained data for a fresnoite composition (Ba 2 TiSi 2 O 8 ) glass. Previous pre-edge and Raman data had suggested that this composition glass contained [5] Ti; however, our Ti L -edge data indicate that Ti is almost exclusively [4] Ti, although some [5] Ti may also be present.

The Santa Cruz massif, which forms part of the Ipanema mafic/ultramafic Complex, Minas Gerais, Brazil, has an exposed upward sequence of metadunite, metaharzburgite (including three separate chromitite layers), metapyroxenite, metagabbro, and meta-anorthosite. Primary igneous chromite grains in the main chromitite layer are poikiloblastic and tectonically fragmented, and have a narrow (10–20 μm) margin of chromian spinel. Cataclased chromite fragments are extensively replaced and mantled by chromian spinel; they have a composite margin comprised of an inner zone of more aluminous spinel and an euhedral outer zone of more Cr-rich spinel, representing granulite and amphibolite facies metamorphic events, respectively. The contents of platinum-group elements (PGE) and Au in chromite separates are relatively high (Os 45, Ir 23, Ru 136, Rh 19, Pt 98, Pd 63, and Au 83 ppb), and significantly enriched (∼ 4x) over whole rock values. Platinum-group minerals are not observed and micrometre-sized inclusions of sulfide minerals (chalcopyrite and pentlandite) in relict chromite are rare. However, comparison of mineral proportions in the separated chromite and whole rock shows that the precious metals are hosted predominantly in the relict igneous chromite grains, rather than the secondary chromian spinel and primary and secondary Mg-rich silicates. The major element composition and average chondrite-normalized PGE pattern of the separated chromite correspond to S-poor stratiform chromitite. We suggest that the precious metals accumulated with chromite during crystallization of a S-poor magma, and were not remobilized in the relict chromite during the subsequent high grade metamorphism.

Long-standing uncertainty on the structure type of Na2Ge4O9has been resolved. Sodium tetragermanate has been grown by crystallization from a supercooled melt and its single-crystal X-ray structure has been determined (R=0.022). Sodium tetragermanate is trigonal witha=11.3234(12),c=9.6817(9) Å, space groupP3c1,Z=6, andDx=4.451 g cm−3. The structure is comprised of a mixed tetrahedral–octahedral framework with three-membered [Ge3O9] rings of GeO4tetrahedra interconnected by isolated GeO6octahedra via shared corners and isA2Ge4O9-type. Bond distances and angles for GeO4tetrahedra and GeO6octahedra are very similar to the corresponding values in the type structure of K2Ge4O9, the two structures differing mainly in the accommodation of the smaller (medium–large-sized) Na cation, which is now in a 5+2 coordination. The structure–composition relationships of wadeite-type,A2Ge4O9-type, and Na2Si4O9-type structures of germanates and silicates depend largely on theT–O distance and the size of the monovalent cation. We confirm that sodium tetragermanate is a metastable phase at all pressures up to 2 kbar, the stable assemblage for the Na2Ge4O9composition being sodium enneagermanate (Na4Ge9O20) plus a more sodic phase.

Si K- and L-edge X-ray absorption near-edge structure (XANES) of SiO2-P2O5 and Na2O-SiO2-P2O5 glasses containing P2O5 above 30 mol% were investigated using synchrotron radiation. Both Si K- and L-edge spectra indicate that Si remains fourfold coordinated (Si-[4]) With O in these glasses until the content of P2O5 reaches about 32 mol%, at which sixfold coordinated Si (Si-[6]) first appears. The proportion of Si-[6] increases qualitatively with increase in the content of P2O5. However, several P2O5-rich glasses contain Si-[4] only, possibly pointing to a dependence of Si-[6] content on quench rate. These results are consistent with Si-29 MAS NMR spectra for silicate-phosphate glasses of similar composition. To estimate further the relative proportions of Si-[4] and Si-[6] in these glasses using Si K-edge spectra, model composite materials of a-SiO2, containing ([4])Si only, and c-SiP2O7, containing [6]Si only, were used to establish the correlation of area ratio for Si-[6] and Si-[4] edge features with bulk composition. The regression equation may be used for semiquantitative estimation of relative proportions of Si-[6] and Si-[4] in glasses and other materials of unknown structure with compositions similar to those of the present glass systems.

Ankerite, siderite, calcite and magnesite occur in variable proportions within all host and mineralized rocks of the Bogosu and Prestea mining districts of the Ashanti Gold Belt, Ghana. The compositions of coexisting ankerite-siderite grains establish that complex rhythmically zoned growth banding and replacement textures are present. This compositional variation is attributed to episodic fluctuation in the temperature and composition of fluids in the Bogosu-Prestea mesothermal gold system. Temperatures derived from the ankerite-siderite composition geothermometer are generally consistent with those from calcite-dolomite, arsenopyrite, carbon and oxygen stable isotope, and fluid inclusion geothermometers, and are about 360°C for the metamorphic peak, 400 to 350°C for carbonate alteration of mafic dikes, and 340 to 140°C for gold deposition. The latter range occurs on a thin-section scale and represents separate pulses of fluid in the ore conduit.

Various polyphosphate glasses have been synthesized. O 1s and P 2p photoelectron and high resolution P L-edge x-ray absorption near edge structure (XANES) spectroscopies were used to characterize the polyphosphates. It has been shown that from O 1s photoelectron spectra and P L-edge XANES, it is possible to determine the degree of polymerization of the polyphosphates. Using polyphosphate glasses as model compounds, the nature of phosphorus in tribochemical films generated on steel and thermally deposited films has been investigated. It has been shown that P L-edge XANES spectroscopy is more sensitive than either O 1s or P 2p photoelectron spectroscopy for gaining structural information about the films. Phosphorus always appears as a polyphosphate and the degree of polymerization is related to the alkyl or aryl groups used in ZDDP. No appreciable amount of thiophosphate could be detected.

Polarized S K- and L-edge, Mo L3- and L2-edge x-ray absorption near-edge structure (XANES) of natural molybdenite (2H-MoS2) have been measured with synchrotron radiation. These results are qualitatively interpreted using the energy band model of molybdenite and provide important information on the unoccupied states of molybdenite. The valence band (VB) maximum of molybdenite is characterized by fully occupied Mo 4dz2, and the conduction band (CB) minimum of molybdenite is characterized by unoccupied Mo 4d states. The unoccupied Mo 4d band is split into two sub-bands, designated as t 2g − /t 2g + and e g − /e g + sets. Although the relative energy of these two sets are difficult to be evaluated, probably the former has the lower energy than the latter, both two sets have the combination wave functions of the other unoccupied Mo 4d components, rather than the simple 4dx2 — y2 and 4dxy states. The unoccupied Mo 4d sub-bands contain significant DOS of both S 3 p- and 3 s-like states, indicating strong hybridization with S 3s and 3 p states. In the lower energy sub-band, the DOS of the S pz- and px,y-like states are very similar. However, in the higher energy sub-band, the DOS of the S 3 px,y-like state is lower than that of the S 3pz state. Polarized S K-edge XANES also reveal the features of antibonding S pz- and px,y-like states in molybdenite. The feature assigned to the S 3 pz-like states is stronger and sharper, and shifts to lower energy by about 2 eV relative to that for the S 3 px,y-like states.

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO 4 4− cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al for Si shifts the Si K-edge to lower energy. The chemical shift of Si K-edge is also sensitive to cations in more distant atom shells; for example, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak correlation with average Si-O bond distance (dSi-O), Si-O bond valence (sSi-O) and distortion of SiO4 tetrahedra, due to the crystal structure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.

A variety of LREE-rich minerals are associated with late magmatic-stage platinum-group element (PGE) mineralization [Σ(PGE + Au) = 300 ppb) in unsheared clinopyroxenite and gabbro proximal to sheared amphibolite in the Boston Creek Flow (BCF) Al-depleted komatiitic basalt, Archean Abitibi greenstone belt, Ontario. The LREE-rich minerals are LREE-rich apatite (La2O3 + Ce2O3 ≥ 1.5 wt%), LREE-rich epidote (Ce, La: 12 wt% ΣREE), and bastnaesite [(Ce,La)(CO3)(F,OH)]. The LREE-rich apatite forms rare zones in altered apatite grains and discrete, multifaceted micrometric-sized grains. LREE-rich epidote forms large (up to 100 ,μm), compositionally zones grains in amphibolitized plagioclase. Bastnaesite forms areas marginal to and veinlets within the LREE-rich epidote and analyses are characterized by up to 0.4 wt% Cl. Compared to other unsheared rocks from the flow, the REE-rich mineral host rocks contain: intermediate REE contents (ΣREE = 38 to 71 ppm), Ba contents (up to 240 ppm), and U/Th values (0.3 to 7.2); variable Cl contents (21 to 60 ppm); and slightly elevated δ34S values (up to 3.3). In contrast, the sheared amphibolite is characterized by low contents of REE (ΣREE = 25 ppm), Cl (15 ppm), Ba (20 ppm), U (0.5 ppm), and Th (0.4 ppm), and a distinctive chondrite-normalized whole-rock REE pattern profile [(La/Sm)n = <2 and (Tb/Yb)n = < 1).

The S K and L-edge x-ray absorption near-edge structures (XANES) of low bornite, cubanite, chalcocite, covellite, enargite and tetrahedrite have been measured with synchrotron radiation. The near-edge features are interpreted based on comparison with the S K- and L-edge spectra of chalcopyrite and a MO/energy band structure model. The XANES spectra of these sulfides reflect the DOS of unoccupied S s-, p- and d-like states near and above the Fermi level. In tetrahedral Cu-Fe sulfides, the Fe3+ 3d crystal field band has much more significant DOS of unoccupied S 3p-and 3s-like states than the Cu+ 3d crystal field band. For Cu sulfides, the Cu+ 3d crystal field band has the higher DOS of S 3p- and 3 s-like states in tetrahedral structure than in structures with the triangular CuS3 cluster. The shifts in both S K- and L-edges correlate approximately linearly with the energy gap.

Sulfur K-edge x-ray absorption spectra (XANES and EXAFS) and L-edge XANES of sphalerite (ZnS), chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) have been recorded using synchrotron radiation. The K- and L-edge XANES features are interpreted using a qualitative MO/energy band structure model. The densities of unoccupied states at the conduction bands of sphalerite, chalcopyrite and stannite are determined using S K- and L-edge XANES features (up to 15 eV above the edge), combined with published metal K-edge XANES. The SK- and L-edge XANES also indicate that, for sphalerite, the Fe2+ 3d band at the fundamental gap has little or no bonding hybridization with S 3p and S 3s orbitals; for chalcopyrite, the Cu+ 3d and Fe3+ 3d bands have strong mixing with S 3p and S 3s states, while for stannite the Cu+ 3d band strongly hybridizes with S 3p and S 3s orbitals, but the Fe2+ 3d band does not. The post-edge XANES features (15–50 eV above the edge) of sphalerite, chalcopyrite and stannite are similar. These features are related to the tetrahedral coordination of sulfur in all these structures, and interpreted by a multiple scattering model. The resonance energies from both the K-edge and L-edge XANES for these minerals are well correlated with reciprocal interatomic distances and lattice spaces. Sulfur K-edge EXAFS analyses using Fourier transform and curve fitting procedures are presented. Comparison of the structural parameters from EXAFS with x-ray structure data shows that the first shell bond distances (BD) from EXAFS are usually accurate to ±0.02 Å, and that coordination numbers (CN) are generally accurate to ±20 percent. For sphalerite, EXAFS analysis yields the structure parameters for the first three neighbour shells around a sulfur atom; the BD and CN even for the third shell are in close agreement with the x-ray structure, and the Debye-Waller term decreases from the first shell to the third shell. It is shown that sphalerite (ZnS) is a good model compound for EXAFS analysis of sulfur in chalcogenide glasses and metalloproteins.

Platinum-group minerals (PGM) and native gold are reported in association with gersdorffite ± nickeline from the Thompson mine, Thompson Nickel Belt, Manitoba, Canada. Four PGM-gold-bearing ore types are distinguished on the basis of mineral assemblages and host rocks: I. Irarsite in massive Ni sulphide ore hosted by metapelite; II. Gold, sudburyite, testibiopalladite-antimonian michenerite, unnamed PGM, and merenskyite in As-rich Ni ore hosted by metapelite from the T-1 mine; III. Gold with tellurides in As-rich Ni ore hosted by metapelite from the open pit; and, IV. Gold, majakite, kotulskite, merenskyite, and michenerite in As-rich Ni ore hosted by pegmatite from the T-1 mine. Limited whole-rock assays of II yielded Pt < 10 ppb, Pd 18 ppm, and Au 13 ppm. Native gold is argentian (Ag22-Ag32), and most Ag-rich in pegmatite-hosted samples. Testibiopalladite compositions straddle the previously inferred miscibility gap with michenerite. The unnamed PGM has a composition of (Pd, Ni)0.44(Te, Sb)0.56, and is distinctly anisotropic. Sporadic, minor amounts of PGE (Ru excepted) are present in gersdorffite and nickeline.

Raman spectra of glasses with compositions along the Na2OGeO2 join and corresponding crystalline phases have been investigated using micro-Raman techniques. The main vibrational band in the Raman spectrum of GeO2, which is associated with symmetric stretch of the GeOGe bonds, is observed to contain fine structure. These weak vibrational features may be indicative of several distinct 4-membered ring populations within the network. Changes in the intensity of the fine structure with addition of Na2O indicate that the ring statistics change systematically with composition. No evidence is observed along the join for the formation of 6-fold coordinated germanium atoms. The ‘germanate anomaly’ exhibited by these glasses appears to result from the formation of 3-membered rings of GeO4 tetrahedra. The maximum (or minimum) in the anomaly occurs when the network becomes saturated in 3-membered GeO4 rings. Beyond this point, the continued formation of Q3 tetrahedra (tetrahedra containing 1 NBO) is responsible for the decline (increase) in some properties. The glass structure begins to resemble the crystalline digermanate structure at ≥ 30–35 mol% added Na2O. Crystallization occurs at ∼ 40 mol% Na2O compositions at which large numbers of Q2 tetrahedra form and there is total breakdown of the glass network.

Na 8 (Al 6 Ge 6 O 24 )Cl 2 cristallise dans P43n avec affinement jusqu'a 0,013. Na 8 (Al 6 Ge 6 O 24 )Br 2 cristallise dans P43n avec affinement jusqu'a 0,019. Na 8 (Al 6 Ge 6 O 24 )I 2 cristallise dans P43n avec affinement jusqu'a 0,016

The phase relations in the (Na,K)AlGeO4 system have been investigated at atmospheric pressure over the temperature range 700–1100° C by X-ray powder diffraction and electron diffraction/microscopy. Four distinct structure-types occur in this system including the beryllonite, nepheline, kalsilite and KAlGeO4 types in order of increasing KAlGeO4 content. In contrast to the (Na,K)Al-SiO4 system, the nepheline structure is only stable over a narrow composition range around 25 percent K at temperatures above approximately 800° C and transforms reconstructively into the beryllonite structure at lower temperatures. The formation of domain microstructures in some K-rich phases has been directly observed by high-resolution electron microscopy and can be associated with the presence of diffuse scattering in their diffraction patterns. The structural trend observed across the (Na,K)AlGeO4 series as a function of composition can be rationalized to a large extent in terms of the dependence of the framework topology of these tridymite-derivative structures on the size of the alkali atoms.