Titre du document / Document title

The first occurrence of ewaldite and donnayite-(Y), two rare carbonate minerals, in the Narssârssuk pegmatite, South Greenland

Auteur(s) / Author(s)

PETERSEN O. V. ; BALIC-ZUNIC T. ; GAULT R. A. ; ANDERSEN T. ;

Résumé / Abstract

Ewaldite and donnayite-(Y) have recently been found, epitaxially inter-grown, in crystals from the Narssârssuk pegmatite, South Greenland. They form decidedly hemimorphic and characteristically cone-shaped, individual crystals up to 1.1 mm in diameter and 0.8 mm thick, and aggregates of few crystals grown together in random orientation. These crystals show the forms {0001}, {0001} and {1124}, with overgrowths of thin, hexagonal plates covering the {0001} faces in a three-fold parallel array. They are colourless to white, transparent to translucent. The ewaldite-donnayite-(Y) crystals are found on calcite, with associated minerals being ashcroftine-(Y), ancylite-(Ce), and fluorite along with aegirine, elpidite, feldspar (orthoclase), graphite and polylithionite. The Narssârssuk ewaldite is uniaxial negative. n^ε and n^ω, for λ = 589 nm, are: 1.552(0.5) and 1.653(0.5) respectively. The empirical formulae, based on microprobe analyses, of the Narssârssuk ewaldite and donnayite-(Y) are: (Ba^2.37Sr^0.60)^Σ2.97Na^1.06Ca^0.89(Y^0.38Ce^0.24Nd^0.18 La^0.08Dy^0.06Pr^0.06Sm^0.04Er^0.03)^Σ1.07(CO³)⁶.3H²O, and (Sr^2.09Ba^1.01)^Σ3.10Na^1.11Ca^1.00 (Y^0.40Ce^0.16Nd^0.07La^0.06Dy^0.07Pr^0.05Er^0.06Yb^0.03)^Σ0.90(CO³)⁶.3H²O, respectively, CO² and H²O being calculated by stoichiometry, and their presence confirmed by IR spectroscopy. The crystal lattice parameters of ewaldite are a = 5.294(2) Å, and c = 12.666(4) Å, presumed space group P63mc, and those of donnayite-(Y) are a = 5.20(1) Å, and c = 18.35(4) Å, presumed space group R3m.

Revue / Journal Title

Neues Jahrbuch für Mineralogie Monatshefte   ISSN 0028-3649   CODEN NJMMAW 

Source / Source

2003, n^o12, pp. 543-555 [13 page(s) (article)]

Langue / Language

Anglais
Revue : Multilingue

Editeur / Publisher

Schweizerbart'sche, Stuttgart, ALLEMAGNE  (1950-2004) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 924 A, 35400011579654.0020