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

ABSTRACT The crystal structure of vigrishinite, ideally NaZnTi 4 (Si 2 O 7 ) 2 O 3 (OH)(H 2 O) 4 , a murmanite-group mineral of the seidozerite supergroup from the type locality, Mt. Malyi Punkaruaiv, Lovozero alkaline massif, Kola Peninsula, Russia, was refined in space group C $\bar 1$ , a = 10.530(2), b = 13.833(3), c = 11.659(2) Å, α = 94.34(3), β = 98.30(3), γ = 89.80(3)°, V = 1675.5(2.1) Å 3 and R 1 = 12.52%. Based on electron-microprobe analysis, the empirical formula calculated on 22 (O + F), with two constraints derived from structure refinement, OH + F = 1.96 pfu and H 2 O = 3.44 pfu, is: (Na 0.67 Zn 0.21 Ca 0.05 □ 1.07 ) Σ2 (Zn 0.86 □ 1.14 ) Σ2 (Zn 0.14 □ 0.36 ) Σ0.5 (Ti 2.60 Nb 0.62 Mn 0.30 ${\rm Fe}_{{\rm 0}{\rm. 23}}^{{\rm 2 +}} $ Mg 0.10 Zr 0.06 Zn 0.05 Al 0.03 Ta 0.01 ) Σ4 (Si 4.02 O 14 ) [O 2.60 (OH) 1.21 F 0.19 ] Σ4 [(H 2 O) 3.44 (OH) 0.56 ] Σ4 {Zn 0.24 P 0.03 K 0.03 Ba 0.02 } with Z = 4. It seems unlikely that constituents in the {} belong to vigrishinite itself. The crystal structure of vigrishinite is an array of TS blocks (Titanium Silicate) connected via hydrogen bonds. The TS block consists of HOH sheets (H = heteropolyhedral and O = octahedral) parallel to (001). In the O sheet, the Ti-dominant M O (1,2) sites, Na-dominant M O (3) and □-dominant M O (4) sites give ideally Na□Ti 2 pfu. In the H sheet, the Ti-dominant M H (1,2) sites, Zn-dominant A P (1) and vacant A P (2) sites give ideally Zn□Ti 2 pfu. The M H and A P (1) polyhedra and Si 2 O 7 groups constitute the H sheet. The ideal structural formula of vigrishinite of the form ${\rm A}_{\rm 2}^{P} {\rm M}_{\rm 2}^{\rm H} {\rm M}_{\rm 4}^{\rm O} $ (Si 2 O 7 ) 2 ( ${\rm X}_{\rm M}^{\rm O} $ ) 2 ( ${\rm X}_{\rm A}^{\rm O} $ ) 2 ( ${\rm X}_{{\rm M,A}}^{P} $ ) 4 is Zn□Ti 2 Na□Ti 2 (Si 2 O 7 ) 2 O 2 O(OH)(H 2 O) 4 . Vigrishinite is a Zn-bearing, Na-poor and OH-rich analogue of murmanite, ideally Na 2 Ti 2 Na 2 Ti 2 (Si 2 O 7 ) 2 O 2 O 2 (H 2 O) 4 . Murmanite and vigrishinite are related by the following substitution: H ( ${\rm Na}_{\rm 2}^{\rm +} $ ) mur + O (Na + ) mur + O (O 2– ) mur ↔ H (Zn 2+ ) vig + H (□) vig + O (□) vig + O [(OH) – ] vig . The doubling of the t 1 and t 2 translations of vigrishinite compared to those of murmanite is due to the order of Zn and □ in the H sheet and Na and □ in the O sheet of vigrishinite.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.