17 research outputs found

    Hydrothermal alteration of chevkinite-group minerals: products and mechanisms:Part 1. Hydration of chevkinite-(Ce)

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    Samples from Russia and Scotland are used to examine the interaction of the REE-Ti silicate chevkinite-(Ce) with hydrothermal fluids. Altered zones in crystals are distinguished by using areas of low intensity on backscattered-electron images, low analytical totals, increasingly large departures from stoichiometry and, in some cases, the presence of micropores. Initial alteration of the chevkinite results in strong Ca enrichment. With increasing degrees of alteration, Ca abundances drop sharply, as do those of the REE, Fe and Si. In contrast, Ti levels increase strongly, usually accompanied by higher Nb ± Th levels. The most altered zones contain up to 36 wt.% TiO2 and the formula cannot be expressed in the standard chevkinite formula. In detail, samples follow different alteration trends, presumably reflecting different P, T, f O2 and fluid composition. The Ti enrichment may have been related to a reaction front of dissolution-reprecipitation passing through the outer zones of the original chevkinite, leaving behind a reprecipitated Ti-enriched phase which may or may not be chevkinite

    Hydrothermal alteration of chevkinite-group minerals:Part 2. Metasomatite from the Keivy massif, Kola Peninsula, Russia

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    Chevkinite-(Ce) in a mineralized quartz-epidote metasomatite from the Keivy massif, Kola Peninsula, Russia, underwent at least two stages of low-temperature alteration. In the first, it interacted with hydrothermal fluids, with loss of Ca, Fe, LREE and Si and strong enrichment in Ti. The altered chevkinite was then rimmed and partially replaced by a zone of ferriallanite-(Ce) and davidite-(La), in turn rimmed by a zone of allanite-(Ce) richer in the epidote component. The allanite zone was in turn partially replaced by rutile-titanite-quartz assemblages, the formation of titanite postdating that of rutile. Aeschynite-(Y), aeschynite-(Ce) and REE-carbonates are accessory phases in all zones. The hydrothermal fluids were alkaline, with significant proportions of CO2 and F. At various alteration stages, the Ca, Si ± Al activities in the fluid were high. Formation of the aeschynite is discussed in relation to its stability in broadly similar parageneses; it was a primary phase in the unaltered chevkinite zone whereas in other zones it formed from Nb, Ti, REE and Th released from the major phases

    Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage:interaction with a F-, CO2-rich fluid

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    The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnäsite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb ± Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F- and CO2-rich, with variable levels of Ca activity, and with fO2 mainly between the nickel-nickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral

    THE PYROCHLORE SUPERGROUP OF MINERALS: NOMENCLATURE

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    A new scheme of nomenclature for the pyrochlore supergroup, approved by the CNMNC-IMA, is based on the ions at the A, B and Y sites. What has been referred to until now as the pyrochlore group should be referred to as the pyrochlore supergroup, and the subgroups should be changed to groups. Five groups are recommended, based on the atomic proportions of the B atoms Nb, Ta, Sb, Ti, and W. The recommended groups are pyrochlore, microlite, romite, betafite, and elsmoreite, respectively. The new names are composed of two prefixes and one root name (identical to the name of the group). The first prefix refers to the dominant anion (or cation) of the dominant valence [or H(2)O or rectangle] at the Y site. The second prefix refers to the dominant cation of the dominant valence [or H(2)O or rectangle] at the A site. The prefix "" keno-"" represents "" vacancy"". Where the first and second prefixes are equal, then only one prefix is applied. Complete descriptions are missing for the majority of the pyrochlore-supergroup species. Only seven names refer to valid species on the grounds of their complete descriptions: oxycalciopyrochlore, hydropyrochlore, hydroxykenomicrolite, oxystannomicrolite, oxystibiomicrolite, hydroxycalcioromite, and hydrokenoelsmoreite. Fluornatromicrolite is an IMA-approved mineral, but the complete description has not yet been published. The following 20 names refer to minerals that need to be completely described in order to be approved as valid species: hydroxycalciopyrochlore, fluornatropyrochlore, fluorcalciopyrochlore, fluorstrontiopyrochlore, fluorkenopyrochlore, oxynatropyrochlore, oxyplumbopyrochlore, oxyyttropyrochlore-(Y), kenoplumbopyrochlore, fluorcalciomicrolite, oxycalciomicrolite, kenoplumbomicrolite, hydromicrolite, hydrokenomicrolite, oxycalciobetafite, oxyuranobetafite, fluornatroromite, fluorcalcioromte, oxycalcioromite, and oxyplumboromite. For these, there are only chemical or crystalstructure data. Type specimens need to be defined. Potential candidates for several other species exist, but are not sufficiently well characterized to grant them any official status. Ancient chemical data refer to wet-chemical analyses and commonly represent a mixture of minerals. These data were not used here. All data used represent results of electron-microprobe analyses or were obtained by crystal-structure refinement. We also verified the scarcity of crystal-chemical data in the literature. There are crystalstructure determinations published for only nine pyrochlore-supergroup minerals: hydropyrochlore, hydroxykenomicrolite, hydroxycalcioromite, hydrokenoelsmoreite, hydroxycalciopyrochlore, fluorcalciopyrochlore, kenoplumbomicrolite, oxycalciobetafite, and fluornatroromite. The following mineral names are now discarded: alumotungstite, bariomicrolite, bariopyrochlore, bindheimite, bismutomicrolite, bismutopyrochlore, bismutostibiconite, calciobetafite, ceriopyrochlore-(Ce), cesstibtantite, ferritungstite, jixianite, kalipyrochlore, monimolite, natrobistantite, partzite, plumbobetafite, plumbomicrolite, plumbopyrochlore, stannomicrolite, stetefeldtite, stibiconite, stibiobetafite, stibiomicrolite, strontiopyrochlore, uranmicrolite, uranpyrochlore, yttrobetafite-(Y), and yttropyrochlore-(Y).Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[2008/04984-7]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[2009/09125-5

    Yttriaite-(Y): The natural occurrence of Y 2 O 3 from the Bol'shaya Pol'ya River, Subpolar Urals, Russia

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    abStraCt Yttriaite-(Y), ideally Y 2 O 3 , is a new mineral (IMA2010-039) from the alluvial deposits of the Bol'shaya Pol'ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 µm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of syntheti

    Yttriaite-(Y): The natural occurrence of Y_(2)O_(3) from the Bol’shaya Pol’ya River, Subpolar Urals, Russia

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    Yttriaite-(Y), ideally Y_(2_O_(3), is a new mineral (IMA2010-039) from the alluvial deposits of the Bol’shaya Pol’ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 µm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of synthetic Y_(2)O_(3) are well known. Synthetic Y_(2)O_(3) crystals are colorless to white with a white streak; crystals are transparent with an adamantine luster, while massive Y2O3 is typically translucent with an earthy luster. Synthetic Y_(2)O_(3) has a Vickers hardness of 653.91, which corresponds to 5.5 on the Mohs scale. Synthetic Y_(2)O_(3) crystals have good cleavage on {111}. Yttriaite-(Y) is isotropic; the refractive index measured at 587 nm on synthetic Y_(2)O_(3) is n = 1.931. The empirical chemical formula (mean of 4 electron microprobe analyses) calculated on the basis of 3 O is: Y_(1.98)Dy_(0.01)Yb_(0.01O3). Yttriaite-(Y) is cubic, space group Ia3(overbar), with parameters a = 10.6018(7) Å, V = 1191.62(7) Å3, and Z = 16. The five strongest lines in the powder X-ray diffraction pattern (measured on synthetic Y_(2)O_(3) using synchrotron radiation) are [d_obs in Å (I) (hkl)]: 3.0646 (100) (222), 1.8746 (55) (440), 1.5984 (38) (622), 2.6537 (26) (400), and 4.3356 (14) (211). The mineral name is based on the common name for the chemical compound, yttria

    Filamentation and Self-compression of High-Energy mid-IR Pulses

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    We report self-action of 0.5-TW peak-power few-cycle 4-um pulses in air and bulk dielectrics that is strikingly different compared to the case of near-IR drivers. An example of scalable nonlinear self-compression of 20-mJ is highlighted
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