Données nouvelles sur la laumontite de la zone métamorphique de Libramont, Belgique
Abstract
New mineralogical data on laumontite from the metamorphic zone of Libramont, Belgium. New laumontite occurrences have been discovered at Bertrix, Ochamp and Luchy, in the metamorphic zone of Bastogne-Libramont. Wet chemical analyses lead to compositions close to Ca[Al2Si4O12].4H2O, with a slightly variable water content and a significant amount of potassium (up to 0.76% K2O). Infrared spectra show an ordered distribution of tetrahedral Si and Al, and relatively low hydrogen bonds between zeolitic water and crystal freamework. Laumontite crystallized in rocks fractures, under a presure lower than 3 kbar and a temperature between 170 and 280°C. The presence of albite in quartz veins and of laumontite in rocks fissures indicates a different geochemical behaviour for Na and Ca during this retrometamorphic phase.