Ancylite-(La) from the Ilímaussaq alkaline complex, South Greenland: Contribution to the mineralogy of Ilímaussaq, no. 106
- Autor(en)
- Ole V Petersen, Gerhard Niedermayr, R A Gault, Franz Brandstätter, H I Micheelsen, Gerald Giester
- Abstrakt
The very rare mineral ancylite-(La), first described from the Khibiny alkaline massif, Kola Peninsula, Russia, has been found on the top of the Taseq Slope, in the IliŽmaussaq alkaline complex, South Greenland. There it occurs in a single, late stage, hydrothermal, albitite vein, associated with aegirine, analcime, calcite, catapleiite, dolomite, ferrobustamite, fluorapatite, hemimorphite, an apophyllite group mineral, pectolite, sphalerite and strontianite as well as a new mineral in the eudialyte group, a yet unidentified REE-silicate and an ancylite with Nd dominating the REE elements. The IliŽmaussaq ancylite-(La) forms individual, slightly fanshaped aggregates up to 1 mm, of platy, weakly rose-coloured crystals, showing the forms {010}, {011} and {121}. The ancylite-(La) from IliŽmaussaq is biaxial negative, with 2V = 68(5)°, na = 1.646(2), nß = 1.710(calc), n? = 1.741(5), and has a = c, ß = b and ? = a. Optical sign, refractive indices and 2V are in agreement with those given for ancylite-(La) from the type locality, which, however, allegedly has a = a, ß = b and ? = c. The unit cell parameters of this IliŽmaussaq ancylite-(La), obtained from powder diffraction data, are: a = 5.029(5), b = 8.563(5) and c = 7.302(5) A°, in good agreement with those given for ancylite-(La) from the type locality. Electron microprobe analyses gave: CaO 1.41, SrO 16.71, La2O3 22.94, Ce2O3 3.26, Pr2O3 6.13, Nd2O3 18.00, Sm2O3 0.98, F 0.74, CO2 22.95, H2O 6.70, O = F - 0.31, total 99.51 wt %. CO2 and H2O calculated by stoichiometry, H2O calculated assuming (OH- + F-) = 1 and H2O = 1. This corresponds to the empirical formula (Sr.62Ca.10)S.72 (La54Nd.41Pr.14Ce08Sm .02)S1.19(CO3)2(OH 85F.15)S1 - H2O, Z = 2. This ancylite-(La) is remarkable by having a considerable surplus of REE over (Sr, Ca) in the structure and by having a highly unusual REE composition with very high Nd and Pr and very low Ce. The structure of ancylite-(La) was refined on CCD single crystal data in the space group Pmcn to R1 = 0.032. The unit cell parameters thus obtained are: a = 5,044(1), b = 8.541(2), c = 7.292(1)A°. Details of the structure are in good agreement with data for ancylite-group minerals from the literature, with some indication of a reduction of symmetry to the space group Pm.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Geologisk Museum, Canadian Museum of Nature
- Journal
- Neues Jahrbuch für Mineralogie. Monatshefte
- Band
- 11
- Seiten
- 493-504
- Anzahl der Seiten
- 12
- ISSN
- 0028-3649
- Publikationsdatum
- 2001
- Peer-reviewed
- Ja
- ÖFOS 2012
- 1051 Geologie, Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/5f30dff7-a256-4589-a1e3-46e7bc27bb34