Ln3+ (Ln3+ = La, Nd, Eu, Yb) incorporation in synthetic tourmaline analogues: Towards tourmaline REE pattern explanation

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Marco E. Ciriotti
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Ln3+ (Ln3+ = La, Nd, Eu, Yb) incorporation in synthetic tourmaline analogues: Towards tourmaline REE pattern explanation

Messaggio da Marco E. Ciriotti » ven 24 set, 2021 9:39

Referenza:
▪ Vereshchagin, O., Britvin, S., Wunder, B., Frank-Kamenetskaya, O.V., Wilke, F.D.H., Vlasenko, N.S., Shilovskikh, V.V., Bocharov, V., Danilov, D. (2022): Ln3+ (Ln3+ = La, Nd, Eu, Yb) incorporation in synthetic tourmaline analogues: Towards tourmaline REE pattern explanation. Chemical Geology, (in press).

Abstract:
Tourmaline rare-earth element (lanthanides + Y) patterns could provide valuable geological information as tourmalines are the most abundant borosilicates on Earth and are stable at extreme PT conditions. The lanthanide-bearing tourmalines were synthesized for the first time in a series of high- (4 GPa) and low-pressure (0.2 GPa) hydrothermal experiments. We have found that Ln-content (Ln = La3+, Nd3+, Eu3+ and Yb3+) in synthetic tourmalines varies significantly (1.13–8.35 wt% Ln2O3) with Yb < La ≤ Nd < Eu independent of pressure conditions. Ln-content in synthetic tourmalines, obtained at low pressure is 2–3 times higher, than those from high-pressure experiments. The Nd- and Eu-rich synthetic tourmalines exhibit cathodo- photoluminescence properties (blue and violet luminescence colors for Nd and Eu, respectively), which confirms trivalent state of Ln in tourmaline structure. Single-crystal X-ray diffraction data for synthetic tourmalines (Nd-rich a 15.893(1), c 7.130(1) Å; Eu-rich a 15.903(5), c 7.168(3) Å) show that Eu3+ and Nd3+ occupy the 9-coordinated X-site in the tourmaline structure. The general formula of obtained synthetic tourmalines can be expressed as Ln3+1-x (Mg,Al)3 (Al,Mg)6 (Si6O18) (BO3)3 (OH,O)3(OH,O) (0.05 ≤ x ≤ 0.97). The crystal-chemical features and lanthanide speciation in synthesized tourmalines are herein discussed and compared to natural and synthetic compounds.
Marco E. Ciriotti

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