Original paper
Calcio-ancylite-(Ce) from Ilímaussaq and Narssârssuk, Greenland, Kola peninsula and Polar Urals, Russia; ancylite-(Ce)-calcio-ancylite-(Ce) an isomorphous series
Pekov, I. V.; Petersen, O. V.; Voloshin, A. V.
Neues Jahrbuch für Mineralogie - Abhandlungen Band 171 Heft 3 (1997), p. 309 - 322
17 references
published: May 15, 1997
DOI: 10.1127/njma/171/1997/309
ArtNo. ESP154017103003, Price: 29.00 €
Abstract
Calcio - ancylite - (Ce) is a rare species with an interesting history. When the mineral was first described, it was not named and its type locality was not specified; when found for the second time it was not recognized and when the name “calcio-ancylite” was used for the first time, it was for a calcium-rich ancylite. Since its proper definition, it has only been described from a few localities. The present studies, including microprobe and X-ray diffraction of a large selection of specimens of the ancylite family of minerals, have identified calcio - ancylite - (Ce) at five new localities, in different parageneses: as a component of pseudomorphs after steenstrupine in an albite vein, Lilleelv, Ilímaussaq complex, Greenland; in a single specimen from a feldspar-natrolite vein genetically connected with Narssârssuk, Greenland; in perovskite nests in pyroxenites of the Afrikanda massif, Kola peninsula, Russia, where the crystals are zoned, with cores of ancylite - (Ce) and border zones of calcio-ancylite- (Ce); and in alpine-type veins of both Dodo and Puiva rock crystal deposits, Polar Urals, Russia. Ancylite - (Ce) - calcio - ancylite - (Ce) forms a, probably continuous, isomorphous series. The system is complex: the Ca/Sr ratio varies in all series; Sr-free calcio - ancylite - (Ce) is known from several localities, but all ancylite - (Ce) analyses show the presence of some Ca; intermediate members of this series are characterized by (Sr+Ca)/ΣREE ≈ 0.5 whereas this ratio varies from ≈ 0.5 to 1.0 for end-close Ca/Sr members; the Ca/Sr ratio has a profound influence on the REE composition since Ca-rich phases of the system are more Nd-rich and La-poor in comparison with Sr-rich members. Ancylite - (Ce) and calcio - ancylite - (Ce) X-ray powder diagrams are similar, but sufficiently different to allow a clear distinction between these two minerals: the strong (110) and (011) reflections are the most sensitive to changes in the Ca/Sr ratio, the Ca-rich members having the smallest d-values. So in spite of the fact that calcio - ancylite - (Ce) is a rare mineral, it is found under a wide range of conditions: calcio - ancylite - (Ce) is now known as a late mineral of granitoids, from altered zones of metamorphic rocks, from alpine veins, from high-alkaline rocks and from ultrabasic alkaline massifs. Sr-free calcio - ancylite - (Ce) is typical for granitoids; Sr-rich calcio - ancylite - (Ce) with transition to ancylite - (Ce) is found in alkaline complexes.
Keywords
Calcio - ancylite - (Ce) • ancylite - (Ce) - calcio - ancylite - (Ce) • isomorphous series • Ilímaussaq • Narssârssuk • Greenland • Afrikanda • Kola peninsula and Dodo and Puiva • Polar Urals • Russia