Mn-bearing "oxy-rossmanite" with tetrahedrally coordinated Al and B from Austria: Structure, chemistry, and infrared and optical spectroscopic study
- Autor(en)
- Andreas Ertl, George R. Rossman, Thomas Ludwig, Stefan Prowatke, John M. Hughes
- Abstrakt
Pink, Mn-bearing .oxy-rossmanite. from a pegmatite in a quarry near Eibenstein an der Thaya, Lower Austria, has been characterized by crystal structure determination, chemical analyses (EMPA, SIMS), and optical absorption and infrared spectroscopy. Crystal structure refinements in combination with the chemical analyses give the optimized formulae X(¡á0.53Na0.46Ca0.01) Y(Al2.37Li0.33Mn2+0.25Fe2+0.04Ti4+0.01) ZAl6 T(Si5.47Al0.28B0.25)O18 (BO3)3 V[(OH)2.85O0.15] W[O0.86(OH)0.10F0.04], with a = 15.8031(3), c = 7.0877(3) A, and R = 0.017 for the sample with 2.05 wt% MnO, and X(¡á0.53Na0.46Ca0.01) Y(Al2.35Li0.32Mn2+0.28 Fe2+0.04Ti4+0.01) ZAl6 T(Si5.51Al0.25B0.24)O18 (BO3)3 V[(OH)2.80O0.20] W[O0.86(OH)0.10F0.04] for a sample with a = 15.8171(3), c = 7.0935(2) A, R = 0.017, and 2.19 wt% MnO. Although the structure re¨ nements show signi¨ cant amounts of [4]B, the bond-lengths (¡1.620 A) mask the incorporation of [4]B because of the incorporation of [4]Al. The distances, calculated using the optimized T site occupancies, are consistent with the measured distances. This .oxy-rossmanite. shows that it is possible to have signi¨ cant amounts of [4]B and [4]Al in an Al-rich tourmaline. The .oxy-rossmanite. from Eibenstein has the highest known Al content of all natural tourmalines (¡47 wt% Al2O3; ¡ 8.6 apfu Al). The near-infrared spectrum con¨ rms both that hydroxyl groups are present in the Eibenstein tourmaline and that they are present at a lower concentration than commonly found in other lithian tourmalines. The integrated intensity (850 cm.2) of the OH bands in the single-crystal spectrum of .oxy-rossmanite. from Eibenstein is distinctly lower than for other Li-bearing tourmaline samples (970.1260 cm.2) with OH contents >3.0 pfu. These samples fall on the V site = 3 (OH) line in the ¨ gure de¨ ning covariance of the relationship between the bond-angle distortion (¥òoct2) of the ZO6 octahedron and the distance. On a bond-angle distortion- distance diagram .oxy-rossmanite. from Eibenstein lies between the tourmalines that contain 3 (OH) at the V site, and natural buergerite, which contains 0.3 (OH) and 2.7 O at the V site. No H could be found at the O1 site by re¨ nement, and the spherical electron density in the difference-Fourier map around the O1 site supports the conclusion that this site is mainly occupied by O. The pink color comes from the band at 555 nm that is associated with Mn3+ produced by natural irradiation of Mn2+. This is the ¨ rst time a tourmaline is described that has a composition that falls in the ¨ eld of the previously proposed hypothetical species .oxy-rossmanite.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- California Institute of Technology (Caltech), Universität Heidelberg, Miami University
- Journal
- American Mineralogist: an international journal of earth and planetary materials
- Band
- 90
- Seiten
- 481-487
- Anzahl der Seiten
- 7
- ISSN
- 0003-004X
- Publikationsdatum
- 2005
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105116 Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/092a6875-a1dd-4fef-8175-5fb4789fd661