Titre du document / Document title

TVEITITE-(Y) AND RARE-EARTH ENRICHED FLUORITE FROM AMAZONITE PEGMATITES OF WESTERN KEIVY, KOLA PENINSULA, RUSSIA. GENETIC CRYSTAL-CHEMISTRY OF NATURAL Ca,REE-FLUORIDES

Auteur(s) / Author(s)

PEKOV I. V. ; CHUKANOV N. V. ; KONONKOVA N. N. ; YAKUBOVIOCH O. V. ; MASSA W. ; VOLOSHIN A. V. ;

Résumé / Abstract

Tvcitite-(Y) was found at Rovgora, Western Keivy, Kola Peninsula, Russia, in an albitc-quartz-amazonitc pegmatite vein related to alkaline granite. It occurs as pods up to 10 cm. Its grains (up to 4 cm) are composed of and Ca_11.4Na_1.9Y_4.4Ln_1.4F_42.0 The idealized structural formula (Z= 3) is: (Y,Na)₆(Ca,LREE)₆(Ca,Na,HREE)₆ (Ca,Na)F₄₂, the simplified formula is: (Ca,REE,Na)₁₃(Y,Na)₆F₄₂; space group R3, a = 17.020, c = 9.679 Å. Nine fluorite samples containing from 0 to 18 mole % (REE)F₃ were examined by electron probe, X-ray powder diffraction and IR spectroscopy. The crystal structure of natural yttrofluoritc has been firstly studied (R = 1.47 %): Fm3m, a = 5.493 A, the structural formula is: (Ca_0.82Y_0.12Ln_0.06)F_2.15. Earlier-published and new data show that yttrofluoritc containing (REE)F₃ > 20 mole % and REE-rich fluoritc with LREE >Y (HREE) are metastable under room conditions. In nature tveitite-(Y) is a product of solid-state transformation of metastable yttrofluorite with (REE)F₃> 20 mole % which can also break down to varieties of tveitite-(Y) with different compositions or iveilite-(Y) + stable yttrofluorite. For the formation of tvcitite-(Y), enrichment of the system by not only Y but also light and heavy lanthanides is presumably necessary: LREE and HREE seem stabilizing admixtures which order to different types of Ca-dominant sites in the structure. Tveitite-(Y) and yttrofluorite are geochemical indicators for media not only enriched by Y, Ln and F but also depleted by Na, Ca, CO₂ and P.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva   ISSN 0869-6055 

Source / Source

2008, vol. 137, n^o3, pp. 76-93 [18 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

Nauka, Sankt-Peterburg, RUSSIE, FEDERATION DE  (1992) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400018684655.0070