Monticellite in the Gwena kimberlite (Shaba, Zaïre): evidence of late-magmatic crystallization
Monticellite in the Gwena kimberlite (Shaba, Zaïre): evidence of late-magmatic crystallization
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格韦纳金伯利岩（扎伊尔沙巴）中的蒙蒂塞利特：晚期岩浆结晶的证据
DOI：
10.1180/minmag.1994.058.392.18
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发表时间：
1994
影响因子：
2.7
通讯作者：
D. Demaiffe
中科院分区：
文献类型：
--
作者：
D. Kampata;P. Nixon;J. Salemink;D. Demaiffe
通过氟和/或羟基取代氧来保持电荷平衡。如果确实发生这种情况，O（1）位将被部分占据，这一事实与大的热参数相一致。然而，由Appleton等人（1992）给出的红外吸收光谱和电子探针相分析表明，这种取代即使发生，也只发生在非常少量的情况下。为了检验这一假设，释放了O（1）位点的占用率。尽管该场所的占用率下降至0.93（4），但该值与完全占用率相比小于2 σ，并且R值没有下降。这些结果表明，该位点基本上被完全占据，这一结果与Appleton等人（1992）的化学和红外数据雅阁。因此，大的热参数可能是由位置无序等因素造成的，在大青山矿-（Ce）（位对称性= 3 m）中占据高对称位置的原子中并不少见。高精度的晶体结构研究结果阐明了红透石-大青山石-（Ce）关系;工作还证明了Nkom B waHil ldaqiingshanite（Ce）的理想分子式为Sr 3（REE）I（CO 3）30 aO 4）I，并且在其原子排列中几乎没有或没有羟基或氟的取代。确认
charge balance being maintained by substitution of fluorine and/or hydroxyl for oxygen. If indeed this occurs, the O(1) site would be partly occupied, a fact consistent with a large thermal parameter. However, the infrared absorption spectrum and electron-microprobe analysis of the phase given by Appleton et al. (1992) suggest such substitution occurs only in very small amounts, if at all. To test this hypothesis, occupancy of the O(1) site was released. Although the occupancy of the site dropped to 0.93(4), the value is less than 2 sigma from full occupancy and there was no decrease in the R value. These results suggest that the site is essentially fully occupied, a result in accord with the chemical and infrared data of Appleton et al. (1992). The large thermal parameter may thus result from factors such as positional disorder, not uncommon in atoms occupying positions of high symmetry as O(1) in daqingshanite-(Ce) (site symmetry = 3m). The results of the high-precision crystal structure study described herein elucidate the huntite-daqingshanite-(Ce) relationship; the work also demonstrates that the ideal formula of N k o m b w a Hi l l d a q i n g s h a n i t e ( C e ) is Sr3(REE)I(CO3)30aO4)I, and that there is little or no substitution of hydroxyl or fluorine in its atomic arrangement. Acknowledgements