Structure Refinement of Bazzite from Pegmatitic and Miarolitic Occurrences

The crystal structure of two samples of bazzite, from the Baveno granite, in Piemonte, Italy (type locality, miarolitic occurrence) and from T0rdal, Norway (pegmatitic occurrence), has been retlned. Compared to material from Alpine fissures, these specimens contain greater amounts of heavy alkali ions (Cs+, Rb+, and K+) in the channels and minor quantities of magnesium in the octahedral positions, in agreement with the results of electron-microprobe analyses. In the channels, the Na+ ions lie at the center of the Si601S rings, i.e., in the Wyckoff position b, whereas H20 and the heavier alkali ions occupy the a position. The possibility of partial substitution of silicon by beryllium, which was inferred for bazzite by some authors on the grounds of chemical analysis, has not been confirmed.