The structure of priceite, a basic hydrated calcium borate, by ab initio powder-diffraction methods
Date
2002
Authors
Wallwork, K.
Pring, A.
Taylor, M.
Hunter, B.
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Journal article
Citation
Canadian Mineralogist, 2002; 40(Part 4):1199-1206
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Abstract
The crystal structure of priceite, data and refined to R<inf>wp</inf> = 0.042 and R<inf>p</inf> = 0.030 using the Rietveld method. The monoclinic structure was refined in space group P2<inf>1</inf>/c, a 11.623(1), b 6.976(1), c 12.350(1) Å, β 110.70(1)°, V936.72(1) Å<sup>3</sup>, Z = 4. The structure consists of infinite chains of pairs of borate rings that extend along [100] via corner-sharing; three corner-linked BΦ<inf>4</inf> (Φ: OH<sup>-</sup>, O<sup>2-</sup>, or H<inf>2</inf>O) tetrahedra form one ring linked through a common boron atom to the next ring, composed of two BΦ<inf>4</inf> tetrahedra and one BΦ<inf>3</inf> triangle. Chains of edge-sharing CaΦ<inf>8</inf> polyhedra zigzag along [010]. The borate chains are cross-linked by CaΦ<inf>8</inf> polyhedra via edge- and corner-sharing. There are three borates in addition to priceite, that contain a <3B>-<3B> chain motif, but priceite is the only one containing a 3□ ring. These chains extend perpendicular to the calcium chains of polyhedra, in contrast to colemanite, which displays a <3B> motif where the strings are parallel.