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Thin crystals of rutile, brookite, anatase, and cassiterite were irradiated in situ in the transmission electron microscope using 1.0 MeV Kr ions at 50-300 K. Synthetic rutile and natural cassiterite, with 0.1-0.2 wt% impurities, remain crystalline up to a fluence of 5 x [10.sup.15] ions [cm.sup.-2] without evidence for amorphization at 50 K. Natural brookite and anatase, with 0.3-0.5 wt% impurities, become amorphous at fluences of 8.1 x [10.sup.14] and 2.3 x [10.sup.14] ions [cm.sup.-2], respectively. We have also studied two natural rutile samples containing ~1.7 and 1.2 wt% impurities. These samples became amorphous at 9.2 x [10.sup.14] and 8.6 x [10.sup.14] ions [cm.sup.-2] at 50 K, respectively. Further analyses of the fluence-temperature data for natural brookite, rutile, and anatase give critical amorphization temperatures of 168 [+ or -] 11,209 [+ or -] 8, and 242 [+ or -] 6 K, respectively. Results are briefly discussed with respect to several criteria for radiation resistance, including aspects of the structure, bonding, and energetics of defect formation and migration. Keywords: Ti[O.sub.2] polymorphs, anatase, brookite, rutile, cassiterite, ion irradiation, defect migration DOI: 10.2138/am.2010.3329

Fly ash from a coal-fired power plant was investigated to obtain detailed information on its physical and chemical properties, and to gain an understanding of potential environmental and health impacts associated with its disposal in landfills. The studied material was produced through combustion of Illinois Basin coal and trapped within the power plant by an electrostatic precipitator. It is a fine-grained, low-Ca fly ash containing primarily Si[O.sub.2], [Al.sub.2][O.sub.3], and [Fe.sub.2][O.sup.3], and is enriched in many toxic elements (e.g., Be, Zn, As, Cd, Tl, Pb, and U) by a factor of up to 30 relative to coal. The ash consists of mainly hematite, magnetite, mullite, quartz, and amorphous material. These constituents occur mostly as spherical particles with diameters of less than 13 [micro]m. We examined the physical, chemical, and structural characteristics of individual fly ash particles by scanning and transmission electron microscopy and electron probe microanalysis. The results demonstrate that, with the exception of complex plerospheres, individual particles are chemically fairly homogeneous, but a pronounced compositional variation exists among particles with similar physical and structural attributes. Electron microprobe data document that several trace elements, including U, are partitioned into the Ferich particles. Transmission electron microscopy revealed that various types of small (

Euhedral crystals of purple spinel are associated with calcite and forsterite in the central zone of composite metasomatic veins of the Adamello contact aureole (Northern Italy). In thin section, spinel is generally colorless, but exhibits concentric zones of dark brown color. These zones are aligned parallel to prominent crystal faces and contain abundant anisotropic, lath-shaped inclusions with their long axis oriented in the six directions of spinel. This orientation results from the alignment of [{001}.sub.Geik] and the [{111}.sub.Sp] crystallographic planes. The small (up to approximately 20 x 1 [micro]m) inclusions were identified as geikielite by means of element distribution maps, micro-Raman spectroscopy, and transmission electron microscopy. Electron microprobe data revealed that spinel consists mainly of Mg[Al.sub.2][O.sub.4], with only minor amounts of other components. The overall chemical variation within individual crystals is characterized by a continuous increase in Fe[O.sub.tot] and ZnO from center to rim (0.6-2.1 wt% and The textural relationships between geikielite inclusions and spinel matrix, combined with the analytical data, suggest that geikielite laths represent exsolution features, thus, a miscibility gap exists between Mg-Al-spinel and geikielite. The purple color results from scattering of light by the geikielite inclusions. Spinel with similar features was also observed in metasomatic veins of the Bergell contact aureole (Italy) and in granulite-facies marbles of Southern India.

The pyrochlore subgroup of pyrochlore minerals frequently contain radioactive rare earth elements and heavy metals. Pyrochlore minerals alter easily and predictably under magmatic and hydrothermal conductions when sodium and calcium substitute for other cations, when fluorine substitutes for oxygen, and when radioactive elements decay. They provide a sensitive indicator of the thermodynamic conditions under which their host rocks formed. Specific pathways of alteration for many members of this groups are elaborated.

A study was conducted on the geochemical alteration of pyrochlore group minerals belonging to the microlite group. Microlite was found to be stable at moderate to high aNa+ and aCa2+ and low to moderate aMn2+. Further observations also show that microlite is replaced during the latter stages of granite pegmatite evolution. Microlite proved to be a reliable indicator of geochemical processes in pegmatite emplacement and showed potential in nuclear waste disposal applications.

The hydroxide contents of spessartine-almandine garnets from the Rutherford no. 2 (Virginia), Himalaya (California), and George Ashley Block (California) pegmatites were determined by infrared spectroscopy. The hydroxide content of garnet increases from the wall zone to the core zone of the Rutherford no. 2 and Himalaya pegmatites, consistent with increasing [H.sub.2]O activity during pegmatite crystallization. However, the absolute OH contents differ by about two orders of magnitude for these two suites of garnets, possibly due to the elevated Ca content of the Rutherford no. 2 and the differences in the depth of emplacement. The garnets from the George Ashley Block show significant excursions from this correlation at the positions within the pegmatite where Kleck and Foord (1999) identified disruptions in major- and minor-element trends that they associated with re-injections of magma and subsequent flushing of the dike system. Ease of measurement as well as a relative amplified sensitivity compared to the Mn and Fe trends, make hydrogen an excellent tracer for the evolution of granitic pegmatites.

Davidite (A1-xM21O38) samples from five different geological localities contain approximately 0.2 to 9.5 wt% UO2 (0.02 to 0.65 atoms per formula unit) and <0.1 to 1.3 wt% ThO2 (<0.01 to 0.09 atoms per formula unit). Maximum amounts of other notable cations include 3.7 wt% V2O3, 4.1 wt% Cr2O3, 2.5 wt% Y2O3, 5.6 wt% La2O3, 6.0 wt% Ce2O3, 4.0 wt% MnO, 2.4 wt% ZnO, 2.7 wt% SrO, and 4.9 wt% PbO. As a result of the variation in age and Th-U content, the calculated α decay dose ranges from ~0.2 to 44 x 1016 α/mg (~0.06 to 14.5 dpa). For samples with ages of 275--295 Ma, the critical dose for amorphization based on electron diffraction is ~0.8 x 1016 α/mg. Natural davidite is commonly altered to rutile, ilmenite, titanite, and other minor phases. [ABSTRACT FROM AUTHOR]

Zirconolites based on the replacement of Ti4+ with equimolar amounts of Nb5+ and Fe3+, CaZrTi2-2x NbxFexO7, have been jointly refined using high-resolution neutron powder diffraction and resonant X-ray powder diffraction data, with extra information provided from 57Fe Mössbauer spectroscopy, to determine cation disorder. The results indicate that the CaZrTi2-2x NbxFexO7 series adopts the zirconolite-2M polytype across the range, with the replacement of Ti4+ by Fe3+ and Nb5+ located within the hexagonal tungsten bronze (HTB) layers. Mössbauer spectroscopy shows that Fe3+ preferentially fills the Ti split (C2) site, with secondary filling of the C1 site and no observable occupancy of the C3 site. This has been confirmed by neutron and resonant X-ray diffraction. Niobium has been found to occupy both the C1 and C3 sites with no evidence for occupancy of the C2 site. [ABSTRACT FROM AUTHOR]

Presents a study which determined the hydroxide contents of spessartine-almandine garnets from pegmatites in the United States by infrared spectroscopy. Methods; Results; Discussion.

Recent experiments have shown that microporous gold can be obtained via the oxidative dealloy ing of Au(Ag)-tellurides such as calaverite (AuTe2), krennerite (Au3AgTe8), and sylvanite [(Au,Ag)2Te4] under mild hydrothermal conditions. The same Au textures have been found in natural gold-telluride ores from the Late Miocene epithermal Aginskoe Au-Ag-Te deposit in Kamchatka, Russia. This confirms that natural microporous gold can form via the replacement of telluride minerals. This replacement may take place under hydrothermal conditions, e.g., during the late stage of the ore-depositing event, explaining the wide distribution of "mustard gold" in some deposits. At Aginskoe, the oxidation of Au-tellurides appears to have resulted only in local redistribution of Au and Te, because the associated oxidation of chalcopyrite scavenged the excess Te, inhibiting the crystallization of secondary Te minerals more than a few micrometers in size. Such cryptic mobility may explain the lack of reported secondary Te minerals in many Te-bearing deposits. [ABSTRACT FROM AUTHOR]