Crystal chemistry of cation-exchanged forms of epistolite-group minerals. Part II. Vigrishinite and Zn-exchanged murmanite

Abstract

The crystal structure of vigrishinite, an epistolite-group heterophyllosilicate with essential Zn, has been reinvestigated; the ideal end-member formula is revised to Zn 2 Ti 4-x (Si 2 O 7) 2 O 2 (OH,F,O) 2 (H 2 O,OH,&) 4 with x,1. Structure models of Zn-exchanged forms of murmanite after 5 and 24 hour experiments with 1N ZnSO 4 solution at 90 C have been obtained from single-crystal X-ray diffraction data. The structural formulae are [B1] Ca 0.04 {Na 1.22 (Ti 1.19 Mn 0.60 Nb 0.21)}{ [A1,A2] Zn 1.03 (Ti 1.64 Nb 0.36)[Si 2 O 7 ] 2 }O 2 (O,OH) 2 (H 2 O) 4 for vigrishinite and {Na 1.14 (Ti 1.45 Mn 0.50 Nb 0.05)}{ [A1] Ca 0.77 [A2] Zn 0.13 (Ti 1.85 Nb 0.15)[Si 2 O 7 ] 2 }O 2 (OH,O) 2 (H 2 O) 4 and [B1] Zn 0.15 [B2] Ca 0.18 {Na 1.06 (Ti 1.32 Mn 0.60 Nb 0.08)}{ [A1] Zn 0.70 [A2] Ca 0.12 (Ti 1.74 Nb 0.26)[Si 2 O 7 ] 2 }O 2 (OH,O) 2 (H 2 O) 4 for the 5 and 24 hour Zn-exchanged forms of murmanite, respectively (braces give successively the contents of the octahedral O and heteropolyhedral H sheets). The triclinic (PÀ1) unit-cell parameters are respectively:

From structure topology to chemical composition. XXIV. Revision of the crystal structure and chemical formula of vigrishinite, NaZnTi4(Si2O7)2O3(OH)(H2O)4, a seidozerite-supergroup mineral from the Lovozero alkaline massif, Kola peninsula, Russia

“…Lykova et al . (2015 b ) stated that their structure-refinement results were better than those of Pekov et al . (2013), and hence the structure information of Lykova et al .…”

“…(2013), and hence the structure information of Lykova et al . (2015 b ) takes precedence over that of Pekov et al . (2013).…”

“…Lykova et al . (2015 b ) reported chemical compositions for vigrishinite from the two other localities in the Lovozero alkaline massif (Table 3), refined the crystal structure of vigrishinite from Mt. Alluaiv ( R 1 = 11.95%) and gave the ‘ideal endmember’ formula for vigrishinite as follows: Zn 2 Ti 4− x (Si 2 O 7 ) 2 O 2 (OH,F,O) 2 (H 2 O,OH,□) 4 with x < 1 (Table 2).…”

“…However this is not an end-member formula because it has more than one chemical species at more than one site (Hawthorne, 2002). Further on in the paper, we will refer to this formula as the formula of Lykova et al (2015 b ).

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Compositional and Textural Variations in Hainite-(Y) and Batievaite-(Y), Two Rinkite-Group Minerals from the Sakharjok Massif, Keivy Alkaline Province, NW Russia

“…Some titanosilicates of the seidozerite supergroup, e.g., murmanite and lomonosovite, have similar elements (HOH-blocks) in their structures. These minerals have cation-exchange properties [17,18] and they can be easily leached. According to structural analysis, during leaching, cations remove from O-layer easier, and Na does so almost completely.…”