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@article{1411005, author = {Plášil, Jakub and Škoda, Radek}, article_location = {Praha}, article_number = {2}, doi = {http://dx.doi.org/10.3190/jgeosci.232}, keywords = {shabaite-(Nd); uranyl carbonate; rare-earth elements; crystal structure; mineral evolution}, language = {eng}, issn = {1802-6222}, journal = {Journal of Geosciences}, title = {Crystal structure of the (REE)-uranyl carbonate mineral shabaite-(Nd)}, volume = {62}, year = {2017} }
TY - JOUR ID - 1411005 AU - Plášil, Jakub - Škoda, Radek PY - 2017 TI - Crystal structure of the (REE)-uranyl carbonate mineral shabaite-(Nd) JF - Journal of Geosciences VL - 62 IS - 2 SP - 97-105 EP - 97-105 PB - Česká geologická společnost SN - 18026222 KW - shabaite-(Nd) KW - uranyl carbonate KW - rare-earth elements KW - crystal structure KW - mineral evolution N2 - Shabaite-(Nd) is a rare supergene mineral formed during alteration-hydration weathering of uraninite; its structure has remained unknown until now. Based on single-crystal X-ray diffraction data, shabaite-(Nd) is triclinic, twinned (leading to a pseudo-monoclinic diffraction pattern), space group P-1, with a = 8.3835(5), b = 9.2766(12), c = 31.7519(3) angstrom, alpha = 90.058(3), beta = 89.945(4), gamma = 90.331(4)degrees, V = 2469.3(4) angstrom(3) and Z = 4. The structure was refined from diffraction data to R = 0.060 for 8434 unique observed reflections. The structure of shabaite-(Nd) is based upon finite clusters of polyhedra, the well-known uranyl-tricarbonate cluster (referred to as UTC), the Ca-polyhedra linked to UTC and infinite sheets of Nd-polyhedra with internal Nd-O-C linkages. The infinite sheets of Nd-polyhedra are stacked perpendicular to c; to the UTC are staggered approximately perpendicular to the Nd-based sheets (thus approx. parallel to c), forming electroneutral ({Nd-2(3+)(CO3)(2-)(2)(H2O)(2)}(2+){Ca(H2O)(5)}(2+)[(UO2)(CO3)(3)](4-))(0) layers. Adjacent layers are linked by hydrogen bonds. The ratio of elements in the chemical formula of shabaite-(Nd), obtained from the structure refinement, Nd2Ca[(UO2)(CO3)(3)] (CO3)(2)(H2O)(10.5), Z = 4, was confirmed by an electron-microprobe study. The resulting empirical formula for the average of six analyses is Ca-1.01(Nd0.64Ce0.32Sm0.28Gd0.19Y0.19Pr0.13Dy0.10La0.07Tb0.05Ho0.01)(Sigma 1.98)(UO2)(CO3)(4.98)(H2O)(10.5)(based on 1 U apfu). A discussion of the crystal-structural relationships of shabaite-(Nd) and chemically related minerals is given as well as discussion of complexities of their crystal structures. ER -
PLÁŠIL, Jakub a Radek ŠKODA. Crystal structure of the (REE)-uranyl carbonate mineral shabaite-(Nd). \textit{Journal of Geosciences}. Praha: Česká geologická společnost, 2017, roč.~62, č.~2, s.~97-105. ISSN~1802-6222. Dostupné z: https://dx.doi.org/10.3190/jgeosci.232.
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