Alkali sulfates with aphthitalite-like structures from fumaroles of the tolbachik volcano, kamchatka, russia. iii. solid solutions and exsolutions

NADEZHDA V. SHCHIPALKINA, IGOR V. PEKOV, SERGEY N. BRITVIN, NATALIA N. KOSHLYAKOVA, EVGENY G. SIDOROV

Research output: Contribution to journalArticlepeer-review

Abstract

Six different exsolution types are found in crystals of aphthitalite-group alkali sulfates from exhalations of the active Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. The coexisting minerals in these exsolutions are metathénardite, ideally Na2SO4 (P63/mmc), and vanthoffite, Na6Mg(SO4)4 (P21/c) (Type I); metathénardite and belomarinaite, KNaSO4 (P3m1) (Type II); thénardite, Na2SO4 (Fddd), and aphthitalite, K3Na(SO4)2 (P3m1) (Type III); aphthitalite and arcanite, K2SO4 (Pnma) (Type IV); metathénardite and natroaphthitalite, KNa3(SO4)2 (P3m1) (Type V); and two chemical varieties of metathénardite (Type VI). The exsolution processes occur in crystals belonging to the high-temperature, hexagonal Na2SO4(I) (= metathénardite, P63/mmc) structure type with different K:Na ratios formed at temperatures higher than 500 8C. The similarity and hexagonal close-packed nature of the crystal structures of the coexisting phases, all representatives of aphthitalite-like structure types, cause the coherent conjugation of domains during diffusion and cation ordering in the parent phase. The breakdown of solid solution can be facilitated by the mosaic character of crystals of a parent phase (incoherent grain boundaries) and the presence of coherent twin boundaries. The heating of samples with exsolution Types II and V up to 700 8C over 24 h shows that diffusion of K and Na through the domain borders does not result in the complete disorder of these cations and the extinction of domains with different crystal structures.

Original languageEnglish
Pages (from-to)713-727
Number of pages15
JournalCanadian Mineralogist
Volume59
Issue number4
DOIs
StatePublished - 13 Sep 2021

Scopus subject areas

  • Geochemistry and Petrology

Keywords

  • Aphthitalite
  • Arcanite
  • Belomarinaite
  • Cation ordering
  • Fumarole
  • K2SO4-Na2SO4 system
  • Metathénardite
  • Natroaphthitalite
  • Solid-state transformation
  • Tolbachik volcano

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