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Open AccessArticle

The Site Occupancy Assessment in Beryl Based on Bond-Length Constraints

1
Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, SK-842 15 Bratislava, Slovakia
2
Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 28 Bratislava, Slovakia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(10), 641; https://doi.org/10.3390/min9100641
Received: 20 September 2019 / Revised: 11 October 2019 / Accepted: 15 October 2019 / Published: 18 October 2019
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals)
The site preference for each cation and site in beryl based on bond-length calculations was determined and compared with analytical data. Tetrahedral SiO4 six-membered rings normally have no substitutions which results from very compact Si4+–O bonds in tetrahedra. Any substitution except Be would require significant tetrahedral ring distortion. The Be tetrahedron should also be negligibly substituted based on the bond-valence calculation; the tetrahedral Li–O bond length is almost 20% larger than Be2+–O. Similar or smaller bond lengths were calculated for Cr3+, V3+, Fe3+, Fe2+, Mn3+, Mg2+, and Al3+, which can substitute for Be but also can occupy a neighboring tetrahedrally coordinated site which is completely vacant in the full Be occupancy. The octahedral site is also very compressed due to dominant Al with short bond lengths; any substitution results in octahedron expansion. There are two channel sites in beryl: the smaller 2b site can be occupied by Na+, Ca2+, Li+, and REE3+ (Rare Earth Elements); Fe2+ and Fe3+ are too small; K+, Cs+, Rb+, and Ba2+ are too large. The channel 2a-site average bond length is 3.38 Å which allows the presence of simple molecules such as H2O, CO2, or NH4 and the large-sized cations-preferring Cs+. View Full-Text
Keywords: beryl; site occupancy; crystal chemistry; bond length beryl; site occupancy; crystal chemistry; bond length
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Bačík, P.; Fridrichová, J. The Site Occupancy Assessment in Beryl Based on Bond-Length Constraints. Minerals 2019, 9, 641.

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