Original paper

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

Petersen, O.V.; Balić-Žunić, T.; Gault, R.A.; Andersen, T.

Abstract

Ewaldite and donnayite-(Y) have recently been found, epitaxially intergrown, 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. nε and nω, for λ = 589nm, 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: (Ba2.37Sr0.60)Σ2.97Na1.06Ca0.89(Y0.38Ce0.24Nd0.18 La0.08Dy0.06Pr0.06Sm0.04Er0.03)Σ1.07(CO3)6 · 3 H20, and (Sr2.09Ba1.01)Σ3.10Na1.11Ca1.00(Y0.40Ce0.06Nd0.07La0.06Dy0.07 Pr0.05Er0.06Yb0.03)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.

Keywords

ewalditedonnayite yepitaxynarssarssuk pegmatitegreenland