THE CRYSTAL CHEMISTRY OF MALINKOITE, NaBSiO4, AND LISITSYNITE, KBSi2O6
The crystal structure of malinkoite, NaBSiO4, a 13.8964(4) Å, c 7.7001(2) Å, P63, Z = 18, Dx = 2.922 g cm–3, from the Khibina–Lovozero complex, Kola peninsula, Russia, has been solved by direct methods and refined to an R index of 3.8 % using 2094 unique observed (|Fo |> 4F) reflections collected...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.486.3933 http://rruff.info/doclib/cm/vol39/CM39_159.pdf |
| Summary: | The crystal structure of malinkoite, NaBSiO4, a 13.8964(4) Å, c 7.7001(2) Å, P63, Z = 18, Dx = 2.922 g cm–3, from the Khibina–Lovozero complex, Kola peninsula, Russia, has been solved by direct methods and refined to an R index of 3.8 % using 2094 unique observed (|Fo |> 4F) reflections collected with a single-crystal diffractometer fitted with a CCD detector and MoK X-radiation. Malinkoite is a framework borosilicate with a structure consisting of six-membered rings of regularly alternating (SiO4) and (BO4) tetrahedra, and Na located in the large channels extending along [001]. There are three unique Si sites, each occupied by Si and each coordinated by four O atoms in a tetrahedral arrangement, with <Si–O> distances of 1.625, 1.622 and 1.622 Å, respectively. There are three unique B sites, each occupied by B and each coordinated by four O atoms in a tetrahedral arrangement, with distances of 1.476, 1.476 and 1.473 Å, respectively. There are five unique Na sites, each completely occupied by Na. Three of the Na sites are [9]-coordinated, with <Na–O> distances of 2.626, 2.642 and 2.630 Å, respectively; the remaining two Na sites are [6]-coordinated, with <Na–O> distances of 2.444 and 2.440 Å, respectively. The (SiO4) and (BO4) tetrahedra link to form six-membered rings of two different configurations based on the following sequences of up (U) and down (D) linkages: UDUDUD and UUDUDD in the ratio of 1:2. Nine-coordinated Na polyhedra are located in big cages formed by stacking of UDUDUD rings. Stacking of UUDUDD rings produces smaller cages occupied by [6]-coordinated Na. In accord with the ratio of two types of rings, there are twelve Na octahedra and six [9]-coordinated Na polyhedra per unit cell in malinkoite. The |
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