Publikationsdatum:
2019
Beschreibung:
〈div data-abstract-type="normal"〉〈p〉The new mineral stefanweissite, IMA2018-020, was discovered in sanidinite volcanic ejecta from the Laach Lake (Laacher See) paleovolcano, Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, nosean, biotite, augite, titanite, ferriallanite-(La), magnetite, baddeleyite and a pyrochlore-group mineral. Stefanweissite is brown and reddish-brown, with adamantine lustre; the streak is light brown to yellow. It forms long-prismatic crystals up to 0.03 mm 〈span〉×〈/span〉 0.07 mm 〈span〉×〈/span〉 1.0 mm and acicular crystals up to 2 mm long and 0.02 mm thick typically combined in radiated aggregates in cavities in sanidinite. 〈span〉D〈/span〉〈span〉calc.〈/span〉 = 5.254 g/cm〈span〉3〈/span〉. The mean refractive index calculated from the Gladstone–Dale equation is 2.260. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition is (electron microprobe, wt.%): CaO 7.63, MnO 2.51, FeO 7.86, Al〈span〉2〈/span〉O〈span〉3〈/span〉 0.25, La〈span〉2〈/span〉O〈span〉3〈/span〉 2.28, Ce〈span〉2〈/span〉O〈span〉3〈/span〉 6.54, Pr〈span〉2〈/span〉O〈span〉3〈/span〉 1.01, Nd〈span〉2〈/span〉O〈span〉3〈/span〉 1.59, ThO〈span〉2〈/span〉 3.71, UO〈span〉2〈/span〉 1.09, TiO〈span〉2〈/span〉 17.32, ZrO〈span〉2〈/span〉 28.03, HfO〈span〉2〈/span〉 0.91, Nb〈span〉2〈/span〉O〈span〉5〈/span〉 19.96, total 99.69. The empirical formula based on 14 O atoms per formula unit is Ca〈span〉1.13〈/span〉(Ce〈span〉0.33〈/span〉La〈span〉0.12〈/span〉Nd〈span〉0.08〈/span〉Pr〈span〉0.05〈/span〉)〈span〉Σ0.58〈/span〉Th〈span〉0.12〈/span〉U〈span〉0.03〈/span〉Mn〈span〉0.29〈/span〉Fe〈span〉0.91〈/span〉Al〈span〉0.04〈/span〉Zr〈span〉1.89〈/span〉Hf〈span〉0.04〈/span〉Ti〈span〉1.80〈/span〉Nb〈span〉1.19〈/span〉O〈span〉14〈/span〉. The simplified formula is (Ca,〈span〉REE〈/span〉)〈span〉2〈/span〉Zr〈span〉2〈/span〉(Nb,Ti)(Ti,Nb)〈span〉2〈/span〉Fe〈span〉2+〈/span〉O〈span〉14〈/span〉. Stefanweissite is orthorhombic, with space group 〈span〉Cmca〈/span〉. The unit-cell parameters are: 〈span〉a〈/span〉 = 7.2896(4) Å, 〈span〉b〈/span〉 = 14.1435(5) Å, 〈span〉c〈/span〉 = 10.1713(4) Å and 〈span〉V〈/span〉 = 1048.68(7) Å〈span〉3〈/span〉. The crystal structure was solved using single-crystal X-ray diffraction data. Stefanweissite is an analogue of zirconolite-3〈span〉O〈/span〉 with Nb dominant over Ti in one of two octahedral sites. The strongest lines of the powder X-ray diffraction pattern [〈span〉d〈/span〉, Å (〈span〉I〈/span〉, %) (〈span〉hkl〈/span〉)] are: 2.983(100)(202), 2.897(71)(042), 1.828(38)(154, 400, 333), 1.793(25)(244), 1.767(16)(080), 1.517(10)(282), 1.187(19)(483, 1.11.3, 602). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, with the registration number 5191/1.〈/p〉〈/div〉
Print ISSN:
0026-461X
Digitale ISSN:
1471-8022
Thema:
Geologie und Paläontologie
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