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@article{2334040,
author = {Skřápková, Lenka and Cempírek, Jan and Belley, Philippe M. and Groat, Lee A. and Škoda, Radek},
article_location = {London},
article_number = {5},
doi = {http://dx.doi.org/10.1180/mgm.2023.59},
keywords = {oxy-dravite; crystal structure; Beluga; EMPA; LA-ICP-MS; Al-Mg disorder; Raman spectroscopy},
language = {eng},
issn = {0026-461X},
journal = {Mineralogical Magazine},
title = {Physical properties and crystal structure of near end-member oxy-dravite from the Beluga occurrence, Nunavut territory, Canada},
url = {https://doi.org/10.1180/mgm.2023.59},
volume = {87},
year = {2023}
}
TY - JOUR
ID - 2334040
AU - Skřápková, Lenka - Cempírek, Jan - Belley, Philippe M. - Groat, Lee A. - Škoda, Radek
PY - 2023
TI - Physical properties and crystal structure of near end-member oxy-dravite from the Beluga occurrence, Nunavut territory, Canada
JF - Mineralogical Magazine
VL - 87
IS - 5
SP - 719-730
EP - 719-730
PB - Mineralogical Society
SN - 0026461X
KW - oxy-dravite
KW - crystal structure
KW - Beluga
KW - EMPA
KW - LA-ICP-MS
KW - Al-Mg disorder
KW - Raman spectroscopy
UR - https://doi.org/10.1180/mgm.2023.59
N2 - Oxy-dravite, ideally Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3(O), was found in a composition near its ideal end-member at the Beluga occurrence, Nunavut territory, Canada. It occurs in retrograde albite–muscovite–corundum–calcite domains in a calc-silicate rock. This uncommon oxy-dravite occurs as dark brown, equant to short-prismatic, idiomorphic crystals with vitreous lustre and up to ca. 4 × 3 cm in size. The oxy-dravite is optically uniaxial (–), with ω = 1.6453(5) and ε = 1.6074(18); its calculated density is 3.069 g.cm–3 with a compatibility index of 0.016. The Beluga oxy-dravite has trigonal symmetry, space group R3m with a = 15.9121(2) Å, c = 7.1788(10) Å, V = 1574.12(5) Å3 and Z = 3. The crystal structure was refined to R1 = 1.45 using 1613 unique reflections. The empirical crystal-chemical formula is X(Na0.88Ca0.08□0.03K0.01)Y(Al1.49Mg1.31Fe0.15Ti0.04Zn0.01)Z(Al5.42Mg0.58)T(Si5.84Al0.16O18)B(BO3)3 V(OH2.95O0.05)W(O0.84OH0.01F0.15). Oxy-dravite in nature commonly occurs in a solid solution with foitite, schorl and oxy-schorl. At the Beluga occurrence, its minor contents of Al, vacancy [□], and Ca are most likely compensated by (□Al)(NaR2+)–1 and (CaMg)(NaAl)–1 exchanges of the oxy-magnesio-foitite and magnesio-lucchesiite components. The Beluga occurrence of oxy-dravite is characterised by an Mg-rich environment related to a metamorphic overprint of the original sedimentary sequence. This sequence of marine dolomitic argillaceous marl was influenced by (B,Cl)-rich fluids, probably proximally-derived from mineral breakdown reactions in the calc-silicate during the retrograde stage of metamorphism. The locality is a rare example of a tourmaline + corundum assemblage.
ER -
SKŘÁPKOVÁ, Lenka, Jan CEMPÍREK, Philippe M. BELLEY, Lee A. GROAT and Radek ŠKODA. Physical properties and crystal structure of near end-member oxy-dravite from the Beluga occurrence, Nunavut territory, Canada. \textit{Mineralogical Magazine}. London: Mineralogical Society, 2023, vol.~87, No~5, p.~719-730. ISSN~0026-461X. Available from: https://dx.doi.org/10.1180/mgm.2023.59.
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