Original paper

Leifite from the Ilímaussaq alkaline complex, South Greenland

Petersen, O. V.; Rønsbo, J. G.; Leonardsen, E. S.; Johnsen, O.; Bollingberg, H.; Rose-Hansen, J.

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Neues Jahrbuch für Mineralogie - Monatshefte Jg. 1994 Heft 2 (1994), p. 83 - 90

12 references

published: Feb 7, 1994

DOI: 10.1127/njmm/1994/1994/83

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ArtNo. ESP156199402004, Price: 19.00 €

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Abstract

Leifite has been identified in a specimen from an albitite vein at Tugtup Agtakôrfia in the Ilímaussaq alkaline complex, South Greenland. Ilímaussaq is thus the fifth occurrence of this rare mineral. It forms 1.5 cm, well developed crystals intergrown with albite. The long prismatic leifite crystals show the forms: hexagonal prism I {1010}- striated parallel to the c-axis, hexagonal bipyramid II {1121} and basal pinacoid {0001}. A large number of crystals are regular intergrowths of three or six individuals (trillings) readily interpreted as normal, interpenetration twins with {1010} as the twin planes. Leifite from Ilímaussaq is uniaxial positive with n𝜖 = 1.5204 ±0.0005 and n𝜔 = 1.5148 ±0.0005, for 𝜆= 589 nm. The unit cell dimensions are: a = 14.401 ± 0.007 Å, c = 4.881 ±0.007 Å, cell volume 876.6 Å 3 Both optical properties and unit cell parameters are in good agreement with data obtained for leifite from other localities. Microprobe analyses of leifite from Ilímaussaq, as well as new analyses of leifite from Langesundsfjord, Norway; Mont Saint-Hilaire, Canada; Narssârssuk, South Greenland; and Karnasurt, Kola Peninsula, Russia, are presented. Leifite from Ilímaussaq is chemically zoned, the dominant part has CS2O = 0.23 % and the highest recorded value is CS2O = 1.38 %. The present microprobe investigations of leifite from different localities show that the Na content can exceed 6 atoms per formula unit, the maximum number accounted for in the formula Na6 (Si12 (Si4Al2) (BeX)2O39) • 1.5H2O, X = (OH,F) of Coda et al. (1974). Based on a total of 20 tetrahedrally coordinated cations the formula of leifite from Ilímaussaq is close to Na6K1(Si12(Si3Al3)(BeF) 2O39), it is suggested that the excess of alkalies could be accommodated in the positions where water molecules were located.

Keywords

Leifite • Ilímaussaq alkaline complex • Greenland