Zirconolite with significant REEZrNb(Mn,Fe)O (sub 7) from a xenolith of the Laacher See eruptive center, Eifel volcanic region, Germany
Zirconolite with significant REEZrNb(Mn,Fe)O (sub 7) from a xenolith of the Laacher See eruptive center, Eifel volcanic region, Germany
The Canadian Mineralogist (February 2000) 38, Part 1: 57-65
- Central Europe
- crystal chemistry
- crystal structure
- Eifel
- electron probe data
- Europe
- Germany
- host rocks
- inclusions
- Laacher See
- manganese
- metals
- metasomatism
- monazite
- niobates
- niobium
- oxides
- phosphates
- rare earths
- Rhenish Schiefergebirge
- Rhineland-Palatinate Germany
- X-ray diffraction data
- xenoliths
- zirconolite
Rare, crystalline zirconolite (ideally CaZrTi (sub 2) O (sub 7) ), from xenoliths in pyroclastic formations near Niedermendig, Laacher See eruptive centre, gives an XRD pattern diagnostic of the orthorhombic polytype (zirconolite-2Q), with space group Acam, and a 10.145, b 14.18, c 7.284 Aa. It contains the highest content of Mn reported from natural zirconolite (6 wt.% MnO), and is rich in Nb ( approximately 18 wt.% Nb (sub 2) O (sub 5) ) and REE (< or = 19.4 wt.% Y (sub 2) O (sub 3) + REE (sub 2) O (sub 3) ), Ce being dominant. The mineral formula in terms of three of the five identified end-member components is: 32% CaZrTi (sub 2) O (sub 7) , 53% REEZrMe (super 5+) Me (super 2+) O (sub 7) and 6% ACTZrTiMe (super 2+) O (sub 7) (9% unassigned). Compositional variation is best described by the coupled substitution: REE (super 3+) + (Fe (super 2+) , Mn (super 2+) ) + Nb (super 5+) [] Ca + 2Ti. The host-rock, an alkali syenite xenolith, mainly comprises alkali feldspar (Or (sub 45) Ab (sub 55) ), with minor biotite. Accessory zirconolite crystallized from late-stage, Nb-, Mn- and La-enriched metasomatic fluids in voids between feldspar crystals together with baddeleyite, manganoan magnetite, and monazite-(La).
