Unique W-rich alloy of Os and Ir and associated Fe-rich alloy of Os, Ru, and Ir from California
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Abstract
A shell-like polycrystalline grain (ca. 1 mm) of W-(Mo)-bearing Os-Ir alloy (11.4.18.6 wt% W; up to 1.5% Mo) is present in a very old collection (probably the 1890s) of tiny nuggets from Trinity Co., California. An extensive compositional series [(Os0.43-0.80Ir0.28-0.05) W0.12-0.18], and inverse Ir-Os correlation, are observed; the mean composition [Os0.676W0.153Ir0.124Fe0.021Mo0.015Ru0.011; Σatoms = 1], based on results of 50 electron-microprobe analyses, displays a ratio (Os + Ir):W of 5:1. The observed variations and element correlations suggest that (W + Mo) contents are controlled by Ir, and incorporated via the following substitution scheme: [(W + Mo) + Ir] ↔ Os. The X-ray diffraction data indicate that the W-rich alloy has a hexagonal close-packed structure, related to that of osmium and allargentum, with a = 2.7297(4) Å, c = 4.3377(6) Å, and V = 27.99(1) Å3; the c:a ratio is 1.59. The probable space-group is P63/mmc, and Z = 2; the calculated density is 21.86(1) g/cm3. The W-rich alloy is associated with an Os-Ru-Ir alloy rich in Fe (7.0.9.7 wt%), which exhibits atomic Fe ↔ [Os + Ru] and Ir ↔ [Os + Ru] mechanisms of substitution. We suggest that these W-(Mo)- and Fe-rich alloys formed by metasomatic alteration of a primary Os-Ir-Ru alloy, associated with mineralized ultramafic-mafic rocks of ophiolite afinity. A fluid phase may well have remobilized and transported W, Mo, and Fe. The W-rich alloy likely crystallized from a reducing fluid under conditions of low fugacities of O2 and S2, thus promoting the observed siderophile behavior of W and Mo. These unusual W-(Mo)- and Fe-rich alloy grains were likely derived, as a placer material, from the Trinity ophiolite complex of northern California.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Dana Lecture. Rates of Fe, Mg, Mn, and Ca diffusion in garnet
- An FTIR study of hydrogen in anorthoclase and associated melt inclusions
- First occurrence of iodine in natural sulfosalts: The case of mutnovskite, Pb2AsS3(I,Cl,Br), a new mineral from the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation
- The real topological conÞ guration of the extra-framework content in alkali-poor beryl: A multi-methodological study
- A low-temperature heat-capacity study of synthetic anhydrous Mg-cordierite (Mg2Al4Si5O18)
- Dissolution kinetics of pyrochlore ceramics for the disposition of plutonium
- Oxy-amphibole equilibria in Ti-bearing calcic amphiboles: Experimental investigation and petrologic implications for mantle-derived amphiboles
- Fe2+/Fe3+ charge ordering in contact layers of lamellar magnetism: Bond valence arguments
- Calcic amphibole growth and compositions in calc-alkaline magmas: Evidence from the Motru Dike Swarm (Southern Carpathians, Romania)
- Anomalously high Fe contents in rehomogenized olivine-hosted melt inclusions from oxidized magmas
- The rate of ferrihydrite transformation to goethite via the Fe(II) pathway
- Phase transitions and volumetric properties of cryolite, Na3AlF6: Differential thermal analysis to 100 MPa
- The crystal structure of dissakisite-(La) and structural variations after annealing of radiation damage
- Effects of metal protection coils on thermocouple EMF in multi-anvil high-pressure experiments
- First-principles study of the OH-stretching modes of gibbsite
- In situ X-ray diffraction study of phase transitions of FeTiO3 at high pressures and temperatures using a large-volume press and synchrotron radiation
- High-pressure proton disorder in brucite
- Microhardness, toughness, and modulus of Mohs scale minerals
- Effects of pH, temperature, and aqueous organic material on the dissolution kinetics of meta-autunite minerals, (Na, Ca)2-1[(UO2)(PO4)]2⋅3H2O
- InterstratiÞ ed kaolinite-smectite: Nature of the layers and mechanism of smectite kaolinization
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- An electron microprobe analysis, secondary ion mass spectrometry, and single-crystal X-ray diffraction study of phlogopites from Mt. Vulture, Potenza, Italy: Consideration of cation partitioning
- Unique W-rich alloy of Os and Ir and associated Fe-rich alloy of Os, Ru, and Ir from California
- Schreyerite, V2Ti3O9: New occurrence and crystal structure
- A cold-sealing capsule design for synthesis of fluid inclusions and other hydrothermal experiments in a piston-cylinder apparatus
- Complete solid-solution between Na3Al2(PO4)3 and Mg3Al2(SiO4)3 garnets at high pressure
