Titre du document / Document title

Formanite-(Y) from amazonite randpegmatites of western Keivy tundras (Kola peninsula)

Auteur(s) / Author(s)

VOLOSHIN A. V. ; LYALINA L. M. ; SAVCHENKO Ye. E. ; BOGDANOVA A. N. ;

Résumé / Abstract

Formanite-(Y) was found in amazonite randpegmatites of Ploskaya Mt. It occurs along fractures inside crystals of plumbomicrolite and forms also flattened prismatic crystals on their surface. The mineral is transparent, weakly greenish or colorless. Natural formanite-(Y) is amorphous in X-rays. After 1 hour annealing at + 600 to 850 °C the mineral shows tetragonal modification; at 900 °C temperature it becomes monoclinic. Unit cell parameters of tetragonal and monoclinic modifications are, respectively: a = 5.12(1), c = 10.83(3) Å and a = 5.033(3), b = = 10.874(6), c = 5.279(8) Å, β = 94.81 (7)°. Typical formula of the mineral - ABO⁴, where A = Y, REE, Ca, Th, U; B = Ta, Nb, Ti, Fe. Chemical analyses show insignificant variations of their contents: (Y^0.60-0.81 Yb^0.16-0.30 REE^0.29-0.49)^1.05-1.19(Ta^0.61-0.67Nb^0.23-0.30Ti^0.01-0.02)^0.91-0.98O⁴. In spectrum of REE the light elements (LREE) are entirely absent and the HREE series has distinct ytterbium maximum. The phase heterogeneity of formanite-(Y) is caused by microinclusions of other mineral phases, mainly oxides and sulfides. In evolution of amazonite randpegmatites minerals crystallization of formanite-(Y) is connected with the later stages of Ta-Nb-mineralization reflecting the maximum activity of Ta and the beginning of Y-REE mineralization, namely its early (ytterbium) branch.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva   ISSN 0869-6055 

Source / Source

2003, vol. 132, n^o1, pp. 82-94 [13 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

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

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400011679348.0090