Modular structure of highly ordered eudialyte and its place among hydrated minerals of rastsvetaevite family

The evidence of hydrated proton in eudialyte‐group minerals based on Raman spectroscopy data

“…Hydronium-containing EGMs are also known. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Among EGMs, there are three mineral species approved by the International Mineralogical Association in whose structures H 3 O + cations predominate at one or several N sites: aqualite (H 3 O) 8 (Na,K,Sr) 5 Ca 6 Zr 3 Si 26 O 66 (OH) 9 Cl, [21,22] ikranite (Na,H 3 O) 15 (Ca,Mn,REE) 6 Fe 3+ 2 Zr 3 Si 24 O 66 (O,OH) 6 ClÁnH 2 O, [23,24] and ilyukhinite (H 3 O,Na) 14 Ca 6 Mn 2 Zr 3 Si 26 O 72 (OH) 2 Á3H 2 O. [25,26] In this paper, we provide a low-temperature X-ray structure analysis and vibration spectroscopy study of previously described "potassium-oxonium eudialyte" [19,20] from the Khibiny alkaline massif as well as new data on vibrational spectra and hydrogen bonding of a series of sodium-deficient hydrated EGMs including new samples and minerals whose crystal structures were investigated earlier.…”

“…[17] Hydronium is also a significant component of numerous zirconosilicate minerals belonging to the eudialyte group. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The general formula of eudialyte-group minerals (EGMs) is N1 3 N2 3 N3 3 N4 3 N5 3 M1 6 M2 3-6 M3M4Z 3 (Si 24 O 72 ) Ø 4-6 X 2 . [27,[34][35][36][37] The "rigid" part of the structures of eudialyte-type minerals is a 3D quasi-framework consisting of the IV Si 3 O 9 , IV Si 9 O 27 , and VI M1 6 O 24 rings (M1 = Ca, Mn 2+ , Fe 2+ , Na, Ln, Y, and Sr; coordination numbers are denoted by Roman numerals) connected via M2O 4-7 polyhedra and ZO 6 octahedra (M2 = Fe 2+ , Fe 3+ , Mn 2+ , Mn 3+ , Mg, Zr, Ta, Na; Z = Zr, Ti, Nb) and containing additional M3 and M4 sites that are situated at the centers of two nonequivalent Si 9 O 27 rings and can be occupied by IV Si, VI Nb, VI Ti, or VI W. Extra-framework cations (Na + , K + , Ca 2+ , Mn 2+ , Sr 2+ , Ba 2+ , Pb 2+ , Y 3+ , Ln 3+ , and H 3 O + ) and (in some samples) water molecules occupy five sites, N1-N5, which are typically split and can be partly vacant.…”

New Data on the Isomorphism in Eudialyte-Group Minerals. 1. Crystal Chemistry of Eudialyte-Group Members with Na Incorporated into the Framework as a Marker of Hyperagpaitic Conditions

“…[10] Note: Roman numerals denote coordination numbers. A part of the data corresponds to holotype samples of EGMs: raslakite (12), sergevanite (13), aqualite (14), alluaivite (17), dualite (19), labirinthite (20) and rastsvetaevite (21).…”

New Data on the Isomorphism in Eudialyte-Group Minerals. 2. Crystal-Chemical Mechanisms of Blocky Isomorphism at the Key Sites

“…Megaeudialytes are known only in the Lovozero and Khibiny alkaline massifs, Kola Peninsula [1,4,[73][74][75][76][77][78][79]. Four of them (alluaivite, dualite, labyrinthite, and rastsvetaevite) have been approved by the Commission on New Minerals, Nomenclature, and Classification of the IMA as valid mineral species (see Figures 14 and 15).…”

“…In most cases, the formation of megaeudialytes is regulated by the ordering of the M2-cations. For example, in hydrated rastsvetaevite (Sample 10 in Table 4; see Figure 14c) [75], different population of the M2 and M2* micro-regions (by IV Na 2.7 V Fe 0.3 and V Fe 2.0 V Mn 0.8 , respectively) is the main cause of the unit-cell doubling.…”