Original paper

First occurrence of a Ba-dominant brewsterite: structural features

Cabella, Roberto; Lucchetti, Gabriella; Palenzona, Andrea; Quartieri, Simona; Vezzalini, Glovanna

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European Journal of Mineralogy Volume 5 Number 2 (1993), p. 353 - 360

25 references

published: Apr 19, 1993
manuscript accepted: Nov 30, 1992
manuscript received: Jul 22, 1992

DOI: 10.1127/ejm/5/2/0353

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Abstract

Abstract The first occurrence of brewsterite in Italy, here reported, is at the Cerchiara mine (La Spezia, Liguria); it is found as prismatic crystals filling veins in metacherts from Northern Apennine ophiolitic sequences. Electron microprobe analysis ((Ba1.80Sr0.02Na0.07Ca0.03K0.04) (Al4.29Sin11.78)O32·nH2O) reveals the dominant presence of barium among the exchangeable cations. Cell parameters are: a = 6.790(1), b = 17.581(4), c = 7.735(1) Å, ß = 94.50(3)°. Biaxial (+), nα = 1.514(2), nß = 1.516(2), nγ = 1.528(2). Single crystal refinement confirms the main features of the brewsterite structure, apart from the extraframework cations which seem to be spread over three sites, two of which with low occupancy. This occurrence of brewsterite furnishes new information on the crystal chemistry of this zeolite, up to now reported only as a Sr-dominant zeolite

Keywords

natural zeolite • Ba-dominant brewsterite • Cerchiara mine (La Spezia • Italy) • chemical analysis • optical properties • crystal structure refinement