TEM and X-ray study of syntactic intergrowths of epistolite, murmanite and shkatulkalite

Pèter Nèmeth, Giovanni Ferraris, György Radnóczi, Olga A. Ageeva

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22 Citations (Scopus)

Abstract

Selected-area electron diffraction (SAED) patterns obtained on samples of the heterophyllosilicates epistolite and murmanite from Mt. Malyi Punkaruaiv, Lovozero massif, in the Kola Peninsula of Russia, invariably show broad, streaked and split diffraction-spots and reveal oriented intergrowths (syntaxy) between the two minerals and of epistolite with minor shkatulkalite (likely a heterophyllosilicate as well). These results are confirmed by X-ray single-crystal and powder-diffraction data. We show that the syntaxy is favored by the presence in epistolite, munnanite and shkatulkalite of common supercells, which leads to a systematic overlap of diffraction spots belonging to different intergrown minerals. The structure determination of epistolite and murmanite by using "single-crystal" diffraction intensities contributed also by minor intergrown phases shows substantial residual peaks of electron density and some short bond-lengths. The difficulties encountered in properly refining the structures of the main phases re related to the unresolved contributions of the minor intergrown phases to the diffracted intensities. We suggest the ideal formulae (Na,□)2(Na,Ti)4[Nb2(O,H2 O)4Si4O14](OH,F)2• 2H2O for epistolite and (Na,□)2 (Na,Ti)4[Ti2(O,H2O)4 Si4O14](OH,F)2•2 H2O for murmanite.

Original languageEnglish
Pages (from-to)973-987
Number of pages15
JournalCanadian Mineralogist
Volume43
Issue number3
DOIs
Publication statusPublished - Jun 2005

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Keywords

  • Crystal structure
  • Electron microscopy
  • Epistolite
  • Epitaxy
  • Heterophyllosilicates
  • Mero-plesiotype series
  • Murmanite
  • Shkatulkalite
  • Titanosilicates

ASJC Scopus subject areas

  • Geochemistry and Petrology

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