THE CRYSTAL CHEMISTRY OF NEPHELINE
THE CRYSTAL CHEMISTRY OF NEPHELINE
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霞石的晶体化学成分
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
A. Khomyakov
中科院分区：
文献类型：
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作者：
K. Tait;E. Sokolova;F. Hawthorne;A. Khomyakov
本文报道了采自俄罗斯科拉半岛Khibina-Lovozero杂岩的三个霞石样品的晶体结构：（1）K_（1.91）Na_（6.04）Si_（8.15）Al_（7.72）Fe_（3+ 0.10）O_（32），a_（9.9995）（6），c_（8.384）（2）A，P_（63），Z = 1，Dx = 2.673 g cm-3，（2）K 1.60 Na 6.21 Ca 0.08 Si 8.44 Al 7.43 O 32，a 9.985（1），c 8.372（1）A，P63，Z = 1，Dx 2.660 g/cm 3，得自班克罗夫特，安大略，加拿大，和（3）K 1.76 Na 5.86 Ca 0.13 Si 8.12 Al 7.84 Fe 3+ 0.04 O 32，a 9.9979（6），c 8.3852（2），P63，Z = 1，Dx 2.654 g/cm 3，来自意大利Monte Somma，已使用1273、1191和1364独特观测值将R1指数细化为1.8、2.7和1.7%（|Fo|> 4F）用单晶衍射仪和MoK X-辐射收集的反射。未观察到超结构反射。从[001]往下看，铝硅酸盐四面体出现在63网络的顶点，其中有两种不同类型的六元四面体环：四分之一是以（0，0，z）为中心的近似正六边形环，而其他四分之三是以0 ½ z为中心的扁平六边形环。在这两个环中，四面体的序列都是ududud，上下连接的c形成了一个四连接的三维框架。A位位于沿着0 0 z的通道中，并且对于样品1、2和3，分别在2.97和3.04 A之间由氧原子[9]-配位。霞石（1）中的A位完全被K占据，样品（2）和（3）中的A位部分被K（0.80和0.88）占据。B位点出现在0 ½ z处的通道中，并且分别由2.48和2.79 A之间的氧原子[8]-配位; = 2.633、2.632和2.627 A。B位主要被Na占据[霞石（3）中有少量Ca]。对于所有三个样品，Si和Al在骨架的T位置上高度有序：T（1，4）= Al，= 1.731，1.723和1.732，= 1.736，1.728和1.734; T（2，3）= Si，= 1.606，1.603和1.605，= 1.616，1.615和1.616 A。对于Khibina-Lovozero复合体中的霞石样品，简化的化学式K2 Na 6 Si 8 Al 8 O32对应于霞石的理想端员式，其中A位完全被K占据，B位完全被Na占据，并且Si和Al在T位完全有序。该样品结晶于低温气成岩活动最后阶段形成的超火山岩中。霞石（2）也形成于低温伟晶环境，在T位上显示出很高的Al-Si有序性。蒙特索玛霞石为高温成因。以前的结构精修表明它的Al-Si分布相当无序，本研究结果表明它具有最大的Al-Si有序度，与以前的29 Si MAS NMR结果雅阁。我们的研究结果表明，霞石具有最大的Al-Si顺序，而不管霞石的起源温度。
The crystal structures of three nepheline samples, (1) K1.91 Na6.04 Si8.15 Al7.72 Fe 3+ 0.10 O32, a 9.9995(6), c 8.384(2) A, P63, Z = 1, Dx = 2.673 g cm –3 , from the Khibina–Lovozero complex, Kola Peninsula, Russia, (2) K1.60 Na6.21 Ca0.08 Si8.44 Al7.43 O32, a 9.985(1), c 8.372(1) A, P63, Z = 1, Dx 2.660 g/cm 3 , from Bancroft, Ontario, Canada, and (3) K1.76 Na5.86 Ca0.13 Si8.12 Al7.84 Fe 3+ 0.04 O32, a 9.9979(6), c 8.3852(2), P63, Z = 1, Dx 2.654 g/cm 3 , from Monte Somma, Italy, have been refined to R1 indices of 1.8, 2.7 and 1.7% using 1273, 1191 and 1364 unique observed (| Fo | > 4F) reflections collected with a single-crystal diffractometer and MoK X-radiation. No superstructure reflections were observed. Viewed down [001], the aluminosilicate tetrahedra occur at the vertices of a 63 net in which there are two distinct types of six-membered rings of tetrahedra: one quarter are nearly regular hexagonal rings centered on (0, 0, z), whereas the other three-quarters are flattened hexagonal rings centered on 0 ½ z. In both rings, the tetrahedra have the sequence ududud, and linkage up and down c forms a four-connected three-dimensional framework. The A site is located in the channel along 0 0 z and is [9]-coordinated by oxygen atoms between 2.97 and 3.04 A; = 2.999, 3.009 and 3.008 A for samples 1, 2 and 3, respectively. The A site is fully occupied by K in nepheline (1), and it is partly occupied by K (0.80 and 0.88) in samples (2) and (3). The B site occurs in the channels at 0 ½ z and is [8]-coordinated by oxygen atoms between 2.48 and 2.79 A; = 2.633, 2.632 and 2.627 A, respectively. The B site is occupied mainly by Na [with minor Ca in nepheline (3)]. For all three samples, Si and Al are highly ordered over the T sites of the framework: T(1,4) = Al, = 1.731, 1.723 and 1.732, = 1.736, 1.728 and 1.734; T(2,3) = Si, = 1.606, 1.603 and 1.605, = 1.616, 1.615 and 1.616 A. For the nepheline sample from the Khibina–Lovozero complex, the simplified chemical formula, K2 Na6 Si8 Al8 O32, corresponds to the ideal end-member formula of nepheline with the A site fully occupied by K, the B site fully occupied by Na, and Si and Al completely ordered at the T sites. This sample crystallized in a hyperagpaitic rock formed at the last stages of low-temperature pneumatolitic activity. Nepheline (2), also formed in low-temperature pegmatitic environment, shows very high Al–Si order at the T sites. The Monte Somma nepheline is of high-temperature origin. Previous refinements of the structure had indicated a fairly disordered Al–Si distribution for it. The present results indicate maximal Al–Si order, in accord with previous 29 Si MAS NMR results. Our results suggest that nepheline exhibits maximal Al–Si order irrespective of temperature of origin of the nepheline.