Davyne, a rare feldspathoid of the cancrinite group, with ideal formula Na4K2Ca2Si6Al6O24(SO4)Cl2, is reported only from the volcanic products of the M. Somma – vesuvius area, Italy. A short review of the laternate fortune of davyne as a mineral species distinct from microsommite, another rare mineral with very similar chemical composition and relate dcell constants, is presented. Davyne is hexagonal, space group P63/m, a = 12.705(4), c = 5.368(3) Å. Its crystal structure has been refined to R = 0.049 using 603 reflections collected with MoK-alpha radiation. The sixfold rings of tetrahedra which build up the structure of the mineral present, at difference from cancrinite and vishnevite, hexagonal shaper and a horizontal symmetry plane. Chains of calcium and chlorine anions develop within the undecahedral cages along the threefold axes. In the large channels along the sixfold axis alkali carions Na+ and K+ together with sulphate groups and chlorine anions are located: their ordering within each single channel is described and discussed. On the basis of the chemical data and the structural results the following formula was derived for our specimen of davyne: (Na4.4K1.5Ca0.1)Ca2(Si5.9Al6.1O24)(SO4)0.6Cl2.8.
|Autori:||BONACCORSI E; MERLINO S; PASERO M|
|Titolo:||Davyne: Its structural relationships with cancrinite and vishnevite|
|Anno del prodotto:||1990|
|Appare nelle tipologie:||1.1 Articolo in rivista|