Original paper
Lovdarite, K4Na12(Be8Si28O72) • 18 H2O, a zeolite-like mineral: structural features and OD character
Merlino, Stefano
European Journal of Mineralogy Volume 2 Number 6 (1990), p. 809 - 818
15 references
published: Dec 14, 1990
manuscript accepted: Jun 18, 1990
manuscript received: Feb 7, 1990
DOI: 10.1127/ejm/2/6/0809
Abstract
Abstract The crystal structure of lovdarite, a beryllo-silicate from Lovozero, is determined and refined to R = 0.082, using 1517 independent reflections; the space group is Pma2, with a = 39.576(1), b = 6.9308(2), c = 7.1526 (3) Å. The crystal chemical formula derived in the structural study is K4Na12(Be8Si28O72) • 18 H2O. The lovdarite structure may be described as a three-dimensional framework of silicon and beryllium tetrahedra with alkali cations and water molecules in the cavities. The most outstanding feature of the structure is the arrangement of five tetrahedra in two three-membered rings, sharing a tetrahedron. Lovdarite is the first recorded example of a framework silicate containing three-membered rings: strain is released by the presence of a beryllium cation in each ring. The OD character of lovdarite - evident from its peculiar diffraction pattern - is discussed on the basis of the structural results; an indication is given of the building layers and possible MDO polytypes are derived
Keywords
lovdarite • crystal structure • zeolite-like mineral • polytypism • OD theory