Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Mineralogical ClassificationRevision of formula and structure of schüllerite

13th Feb 2014 09:11 UTCMarco E. Ciriotti Manager

Reference:

▪ Sokolova, E., Hawthorne, F.C., Abdu, Y.A. (2013): From structure topology to chemical composition. XV. Titanium silicates: Revision of the crystal structure and chemical formula of schüllerite, Na2Ba2Mg2Ti2(Si2O7)2O2F2, from the Eifel Volcanic Region, Germany. Canadian Mineralogist, 51, 715-725.

Abstract:

The crystal structure of schüllerite, ideally Na2Ba2Mg2Ti2(Si2O7)2O2F2, a 5.396(1), b 7.071(1), c 10.226(2) Å, α 99.73(3), β 99.55(3), γ 90.09(3)°, V 379.1(2) Å3, Z = 1, from the Eifel volcanic region, Germany, has been refined in the space group P-1 to R = 1.33% using 2247 observed (Fo > 4σF) reflections collected with a single-crystal Bruker D8 three-circle diffractometer equipped with a rotating-anode generator (MoKα radiation), multilayer optics and an APEX-II detector. The empirical formula for schüllerite was calculated on the basis of 18 (O + F) anions: (Na1.10Ca0.43Mn0.30Fe2+0.17)∑2(Ba1.57Sr0.14K0.14□0.15)∑2 (Mg0.79Fe2+0.71Na0.33Fe3+0.17)∑2 (Ti1.67Fe3+0.21Nb0.09Zr0.02Al0.01)∑2Si3.95O15.93F2.07, Dcalc.= 3.879 g/cm3, Z = 1, with Fe3+/(Fe2++Fe3+) ratio determined by Mössbauer spectroscopy. Schüllerite is a Group-IV TS-block mineral: Ti + Mg = 4 apfu. The crystal structure of schüllerite is an alternation of TS (Titanium Silicate) and I (intermediate) blocks of the ideal composition 4− and 4+, respectively. The TS block is composed of the central O (octahedral) sheet and two adjacent H (heteropolyhedral) sheets. In the O sheet, there are two brookite-like chains of MO octahedra of the following ideal compositions: 12− and 14− ; the ideal composition of the O sheet is 0. The H sheet is composed of the <5>-coordinated Ti-dominant MH polyhedra and Si2O7 groups; the composition of the two H sheets is 4−. In schüllerite, the TS block has a topology characteristic of Group IV of TS-block minerals: two H sheets connect to the O sheet such that two Si2O7 groups link to the Mg-dominant octahedra of the O sheet adjacent along t1. In the O sheet, occurrence of divalent cations at the MO(1) site results in the presence of monovalent anions, F−, at the XOA site. The AP site of the H sheet is occupied mainly by Ba; the AP site is shifted from the plane of the H sheet, and Ba atoms constitute the I block of the composition 4+. Schüllerite is the only mineral of Group IV that has (1) a brookite-like 12− chain of octahedra in the O sheet; (2) <5>-coordinated Ti in the H sheet; (3) Ba atoms in the I block. The ideal structural formula of schüllerite is of the form AP2MH2MO4(Si2O7)2(XOM)2(XOA)2 : Ba2Ti2Na2Mg2Ti2(Si2O7)2O2F2, Z = 1.

16th Feb 2014 11:11 UTCGuenter Blass

Hello Marko,

I need the full article!

Do you have of them a PDF file?

nice Sunday

Günter

17th Feb 2014 12:05 UTCMarco E. Ciriotti Manager

Sent!

Ciao.

17th Feb 2014 16:51 UTCGuenter Blass

Marco,

many thanks,

Günter

18th Feb 2014 15:20 UTCUwe Kolitsch Manager

Have amended the abstract to show the correct space group (P-1).

(The originally described structure, determined on a different crystal, was modelled in P1).

18th Feb 2014 15:23 UTCUwe Kolitsch Manager

Schüllerite page updated.

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 18, 2024 01:28:16

Go to top of page