Polyhedron distortions in tourmaline
Polyhedron distortions in tourmaline
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DOI：
10.2113/gscanmin.40.1.153
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发表时间：
2002-02-01
影响因子：
0.9
通讯作者：
Marler, B
中科院分区：
文献类型：
--
作者：
Ertl, A;Hughes, JM;Marler, B
已针对不同化学成分的电气石中的阳离子多面体计算了畸变参数[Δ、σ(2)、DI(Y - O)、DI(O - Y - O)、DI(O - O)]。在YO₆八面体中含有较多小的、高电荷离子的电气石，其Y处的键长畸变更大。Y位占据离子的大小和电荷已包含在一个经验确定的公式中，该公式旨在评估YO₆八面体的键长畸变。此方程表明，YO₆八面体中的键长畸变是Y位占据离子大小和电荷的函数，并且可由这些占据离子预测（观测到的与计算出的畸变的相关系数r = 0.972）。电气石中Z八面体的畸变在很大程度上是该电气石[对于所有O₃被3(OH)每分子式单位（apfu）占据的电气石，相关系数r = -0.985]的函数，尽管O - 3位的占据离子也会影响该畸变。TO₄四面体的键长畸变较小，但对四面体角度畸变的研究表明，它与X位的电荷有很强的协方差（相关系数r = 0.892）。最后，发现XO₉多面体的畸变与Y位占据离子的电荷以及氟含量相关（相关系数r = 0.881）。
Distortion parameters [Delta, sigma(2), DI(Y-O), DI(O-Y-O), DI(O-O)] have been calculated for cation polyhedra in tourmalines of different chemical compositions. Tourmalines with greater amounts of small, highly charged ions in the YO6 octahedron display greater bond-length distortion in Y. The size and charge of the occupants at the Y site have been included in an empirically determined formula intended to evaluate the bond-length distortion of the YO6 octahedron. This equation demonstrates that the bond-length distortion in the YO6 octahedron is a function of the size and charge of the Y-site occupants, and is predictable from those occupants (r = 0.972 for observed versus calculated distortion). The distortion of the Z octahedron in a tourmaline is largely a function of the of that tourmaline [r = -0.985 for all tourmalines where 03 is occupied by 3 (OH) apfu], although the occupant of the O-3 site also affects that distortion. The bond-length distortion of the TO4 tetrahedron is small, but examination of the angle distortion of the tetrahedron demonstrates a strong covariance with the charge at the X site (r = 0.892). Finally, distortions in the XO9 polyhedron were found to correlate with the charge of the occupants at the Y site and the fluorine content (r = 0.881).