Titre du document / Document title

The crystal chemistry of Shcherbakovite from the Khibina Massif, Kola Peninsula, Russia

Auteur(s) / Author(s)

UVAROVA Yulia A. ; SOKOLOVA Elena ; HAWTHORNE Frank C. ;

Résumé / Abstract

The crystal structure of shcherbakovite from Mount Rasvumchorr, Khibina massif, Kola Peninsula, Russia, ideally K² Na Ti₄₊2O(OH) [Si⁴O¹²], a 8.1538(4), b 10.5569(5), c 13.9882(6) Å, V 1204.1(2) Å₃, space group Imma, Z = 4, D^calc 3.194 g/cm₃, has been refined to R¹ = 3.2% for 960 unique (F^o > 4σF) reflections collected on a Broker single-crystal P4 diffractometer equipped with a CCD detector and MoKα X-radiation. Shcherbakovite occurs in late (hydrothermal) shallowly dipping veins of natrolite and is associated with natrolite, aegirine, K-feldspar, strontian apatite, titanite, spherulitic baryllite and rare pyrrhotite and chalcopyrite. Electron-microprobe analysis gave SiO² 40.57, TiO² 18.87, Fe²O³ 1.05, MnO 0.06, BaO 6.7, CaO 0.20, K²O 13.22, Na²O 5.59, Nb²O⁵10.49, SrO 0.08, ZrO² 0.84, Ta²O⁵ 0.06, (H²O)^calc 0.73, sum 97.83 wt.%. The amount of H²O was determined from crystal-structure analysis. There is one tetrahedrally coordinated T site, <T-O> 1.607 Å, occupied by Si. There are two octahedrally coordinated sites, M(1), occupied by (Ti^0.68Nb^0.32 □^1.00), with <M(1)-O> = 2.016 Å, and M(2), occupied by (Ti^0.72 Nb^0.15 Fe₃₊0.08 Zr^0.04 □^1.01), with <M(2)-O> = 1.999 Å. The M(1) and M(2) sites are separated by 0.477 Å, and hence cannot be occupied simultaneously at a local level. There are three interstitial A sites: the A(1) site is [9]-coordinated and is occupied by (K^0.66 Ba^0.23 Na^0.07 Ca^0.02), with <A(1)-O> = 2.952 Å; the A(2) site is [8]-coordinated and is occupied by K, with <A(2)-O> = 2.861 Å, and the A(3) site is [6]-coordinated and is occupied by Na, with <A(3)-O> = 2.493 Å. Shcherbakovite is a K-analogue of batisite, ideally Ba Na²Ti₄₊2O² [Si⁴O¹²]. Shcherbakovite is related to batisite by substitution of K for Ba and K for Na. "Noonkanbahite", ideally Ba K Na Ti₄₊2 O² [Si⁴O¹²], has never been approved by the IMA as a new mineral species. Based on the crystal chemistry of this structure type, the general formula of these minerals may be written as A B C M² Φ² [Si⁴O¹²], with the following end-member compositions: batisite A = Ba, B = Na, C = Na; shcherbakovite, A = K, B = K, C = Na; "noonkanbahite", A = Ba, B = K, C = Na; unnamed, A = K, B = Na, C = Na. acceptée par l'IMA comme nouvelle espèce minérale. Selon la cristallochimie de ce type de structure, la formule générale de ces minéraux serait A B C M² Φ² [Si⁴O¹²], avec les pôles suivants: batisite, A = Ba, B = Na, C = Na; shcherbakovite, A = K, B = K, C = Na; "noonkanbahite", A = Ba, B = K, C = Na; espèce sans nom, A = K, B = Na, C = Na.

Revue / Journal Title

Canadian mineralogist   ISSN 0008-4476   CODEN CAMIA6 

Source / Source

2003, vol. 41 (5), pp. 1193-1201 [9 page(s) (article)]

Langue / Language

Anglais
Revue : Multilingue

Editeur / Publisher

Mineralogical Association of Canada, Ottawa, On, CANADA  (1957) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 12015, 35400011341428.0090