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  • Mineralogical Society  (2)
  • 1
    Online Resource
    Online Resource
    Mineralogical classification and crystal water characterisation of beryl from the W–Sn–Be occurrence of Xuebaoding, Sichuan province, western China
    Mineralogical Society ; 2021
    In:  Mineralogical Magazine Vol. 85, No. 2 ( 2021-04), p. 172-188
    Details
    In: Mineralogical Magazine, Mineralogical Society, Vol. 85, No. 2 ( 2021-04), p. 172-188
    Abstract: Beryl from Xuebaoding, Sichuan Province, western China is known for its unusual tabular habit and W–Sn–Be paragenesis in a greisen-type deposit. The crystals are typically colourless transparent to pale blue, often with screw dislocations of hexagonal symmetry on the (0001) crystal faces. Combining electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry with single-crystal X-ray diffraction (XRD), correlated with Raman and micro-infrared (IR) spectroscopy and imaging, the crystal chemical characteristics are determined. The contents of Na + (0.24–0.38 atoms per formula unit (apfu)) and Li + up to 0.38 apfu are at the high end compared to beryl from other localities worldwide. Li + substitution for Be 2+ on the tetrahedral (T2) site is predominantly charge balanced by Na + on the smaller channel (C2) site, with Na + ranging from 91.5% to 99.7% (apfu) of the sum of all other alkali elements. Cs + and minor Rb + and K + primarily charge balance the minor M 2+ substitution for Al 3+ at the A site; all iron at the A site is suggested to be trivalent. The a axis ranges from 9.2161(2) to 9.2171(4) Å, with unit-cell volume from 678.03(3) to 678.48(7) Å 3 . The c/a ratio of 1.0002–1.0005 is characteristic for T2-type beryl with unit-cell parameters controlled primarily by Be 2+ substitution. Transmission micro-IR vibrational spectroscopy and imaging identifies coordination of one or two water molecules to Na + (type IIs and type IId, respectively) as well as alkali free water (type I). Based on IR absorption cross section and XRD a C1 site water content of 0.4–0.5 apfu is derived, i.e. close to 50% site occupancy. Secondary crystal phases with a decrease in Fe and Mg, yet increase in Na, suggest early crystallisation of aquamarine, with goshenite being late. With similar crystal chemistry to beryl of columnar habit from other localities worldwide, the tabular habit of Xuebaoding beryl seems to be unrelated to chemical composition and alkali content.
    Type of Medium: Online Resource
    ISSN: 0026-461X , 1471-8022
    URL: Article
    DOI: 10.1180/mgm.2021.13
    RVK:
    TE 1000
    Language: English
    Publisher: Mineralogical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2034522-7
    SSG: 13
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Rare-earth crystal chemistry of thalénite-(Y) from different environments
    Mineralogical Society ; 2018
    In:  Mineralogical Magazine Vol. 82, No. 2 ( 2018-04), p. 313-327
    Details
    In: Mineralogical Magazine, Mineralogical Society, Vol. 82, No. 2 ( 2018-04), p. 313-327
    Abstract: Thalénite-(Y), ideally Y 3 Si 3 O 10 F, is a heavy-rare-earth-rich silicate phase occurring in granite pegmatites that may help to illustrate rare-earth element ( REE ) chemistry and behaviour in natural systems. The crystal structure and mineral chemistry of thalénite-(Y) were analysed by electron microprobe analysis, X-ray diffraction and micro-Raman spectroscopy from a new locality in the peralkaline granite of the Golden Horn batholith, Okanogan County, Washington State, USA, in comparison with new analyses from the White Cloud pegmatite in the Pikes Peak batholith, Colorado, USA. The Golden Horn thalénite-(Y) occurs as late-stage sub-millimetre euhedral bladed transparent crystals in small miarolitic cavities in an arfvedsonite-bearing biotite granite. It exhibits growth zoning with distinct heavy-rare-earth element ( HREE ) vs . light-rare-earth element ( LREE ) enriched zones. The White Cloud thalénite-(Y) occurs in two distinct anhedral and botryoidal crystal habits of mostly homogenous composition. In addition, minor secondary thalénite-(Y) is recognized by its distinct Yb-rich composition (up to 0.8 atoms per formula unit (apfu) Yb). Single-crystal X-ray diffraction analysis and structure refinement reveals Y-site ordering with preferential HREE occupation of Y2 vs . Y1 and Y3 REE sites. Chondrite normalization shows continuous enrichment of HREE in White Cloud thalénite-(Y), in contrast to Golden Horn thalénite-(Y) with a slight depletion of the heaviest REE (Tm, Yb and Lu). The results suggest a hydrothermal origin of the Golden Horn miarolitic thalénite-(Y), compared to a combination of both primary magmatic followed by hydrothermal processes responsible for the multiple generations over a range of spatial scales in White Cloud thalénite-(Y).
    Type of Medium: Online Resource
    ISSN: 0026-461X , 1471-8022
    URL: Article
    DOI: 10.1180/minmag.2017.081.044
    RVK:
    TE 1000
    Language: English
    Publisher: Mineralogical Society
    Publication Date: 2018
    detail.hit.zdb_id: 2034522-7
    SSG: 13
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
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