Davyne is a feldspathoid which belongs to the cancrinite group of minerals. A K-free and Cl-rich variety of davyne from Zabargad (St. John) Island, Red Sea, is described from a chemical and structural point of view. It has space group P63, a = 12.763(2), c = 5.336(1) Å, chemical formula Na5.5Ca2.5Si6Al6O24Cl2.5(SO4). The cages present the characteristic Ca-Cl-Ca-Cl... chains, whereas the large channels of the structure contain sodium and minor calcium cations, sulfate groups and additional chlorine anions: the peculiar distribution of the ions in the channels is described and discussed. The large crystals of davyne have been probably formed through the metasomatic action of hypersaline fluids on the metabasalts of the island and were subsequently affected by an alteration process which producted a lot of phases among which the most abundant is a phyllosilicate of "septichlorite"-type.
Davyne from Zabargad (St. John’s) Island: peculiar chemical and structural features
BONACCORSI, ELENA;MERLINO, STEFANO;PASERO, MARCO
1992-01-01
Abstract
Davyne is a feldspathoid which belongs to the cancrinite group of minerals. A K-free and Cl-rich variety of davyne from Zabargad (St. John) Island, Red Sea, is described from a chemical and structural point of view. It has space group P63, a = 12.763(2), c = 5.336(1) Å, chemical formula Na5.5Ca2.5Si6Al6O24Cl2.5(SO4). The cages present the characteristic Ca-Cl-Ca-Cl... chains, whereas the large channels of the structure contain sodium and minor calcium cations, sulfate groups and additional chlorine anions: the peculiar distribution of the ions in the channels is described and discussed. The large crystals of davyne have been probably formed through the metasomatic action of hypersaline fluids on the metabasalts of the island and were subsequently affected by an alteration process which producted a lot of phases among which the most abundant is a phyllosilicate of "septichlorite"-type.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
