Steiningerite, Ba₂Zr₂(Si₄O₁₂)O₂, a new cyclosilicate from the Löhley quarry, Germany

Autor(en)

Rafal Juroszek, Biljana Krüger, Uwe Kolitsch, Günther Frenz, Günter Blaß

Abstrakt

The new mineral steiningerite, ideally Ba₂Zr₂(Si₄O₁₂)O₂, was discovered along fissures and in
cavities in melilite nephelinite samples retrieved from the currently active Löhley quarry,
Eifel Volcanic Fields, Germany. Steiningerite is associated with minerals of the pyroxene
group (augite-diopside), leucite, perovskite, titanite and accessory fluorapatite, fresnoite,
wöhlerite, götzenite, fersmanite, magnetite and minerals of the pyrochlore group. It usually
forms colourless or creamy white, euhedral, short prismatic to thick tabular, partly
pseudocubic crystals up to 100 μm in size but also rarely occurs as individuals reaching 0.5
mm in size. The mineral is transparent to translucent, exhibits vitreous lustre and no visible
cleavage. The calculated density of steiningerite is 3.78 g/cm³. Optically, steiningerite is nonpleochroic and uniaxial positive, with ω = 1.711(3), ε = 1.750(3) (λ = 589 nm). The empirical
formula of holotype steiningerite, calculated on 14 anions, is
(Ba_1.36K_0.56Na_0.09Sr_0.05Ca_0.02)_Σ2.08(Zr_1.52Ti_0.25Nb_0.13U_0.05Fe_0.02Hf_0.01)_Σ1.98(Si_4.00Al_0.03)_Σ4.03O₁₂
(O_1.59F_0.41)_Σ2.00. Steiningerite crystallises in space group P4/mbm, with refined unit-cell parameters a = 8.894(2) Å, c = 8.051(2) Å, V = 636.9(3) Å3, Z = 2. The crystal structure, determined from single-crystal intensity data, was refined to R = 0.0310 for 444 unique reflections with I >3σ(I). The mineral is isotypic with the synthetic KTaSi₂O₇ and structurally similar to the mineral rippite, K₂(Nb,Ti)₂(Si₄O₁₂)(O,F)₂. The hetero-polyhedral framework is formed by the chains of (Zr,Ti)O₆ octahedra, running parallel to the four-fold axis, which are combined via Si₄O₁₂ rings. Each (Zr,Ti)O₆ octahedron shares four vertices with four SiO₄ tetrahedra, belonging to four different Si₄O₁₂ units. This arrangement of atoms creates channels along the c axis, with a pentagonal cross-section, in which charge-balancing Ba²⁺ and K⁺ ions are located. Extra-framework alkaline and alkaline-earth cations have twelve-fold coordination.
The occurrence of the new mineral in a melilite nephelinite, along with its high-temperature
mineral association and the absence of H₂O and OH groups, confirmed by Raman and FTIR
spectroscopies, indicate high-temperature conditions of formation and suggests a
pneumatolytic origin of steiningerite.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

University of Silesia in Katowice, Leopold-Franzens-Universität Innsbruck, Naturhistorisches Museum Wien (NHM), Privat

Journal

Mineralogical Magazine

Band

1

ISSN

0026-461X

DOI

https://doi.org/10.1180/mgm.2024.102

Publikationsdatum

2024

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/59ce208f-f55f-40d7-b58a-037d760c3498