Vanadium-rich muscovite from Austria: Crystal structure, chemical analysis, and spectroscopic investigations

John M. Hughes1, Andreas Ertl2, Heinz-Jürgen Bernhardt3, John Rakovan1,  and George R. Rossman4

1Department of Geology, Miami University, Oxford, OH 45056, U.S.A.
2Institut für Mineralogie und Kristallographie, Geozentrum, Universität Wien, Althanstraße 14, A-1090 Vienna, Austria
3Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44801 Bochum, Germany
4Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125-2500, U.S.A.


Abstract

The crystal structure of a green, transparent, vanadium-rich 2M1 muscovite  (V2O3 = 11.35 wt%, the highest amount reported to date in muscovite) with the optimized formula (K0.94Na0.06) (Al1.20V3+0.61Mg0.12Cr3+0.07) (Si1.54Al0.46)T 1 (Si1.54Al0.46)T 2 O10 (OH)2 and space group C2/c, a = 5.2255(6), b = 9.070(1), c =  20.032(2) Å, b = 95.773(2)º, Z = 4 has been refined to R = 7.2% for 1,037 unique reflections (Mo Ka). This muscovite, which occurs in small quartz dikes in graphite schist from Weinberg Mountain, near Amstall village, Lower Austria, is distinctly low in Cr (Cr2O3: ~1.4 wt%) and in Mg (MgO: ~1.1 wt%); Fe, Mn and Ti are below the detection limit. All octahedral cations occupy the M2 site, and the average octahedral bond (M2-O) distance is 1.953 Å. Structural distortions to accommodate tetrahedral-octahedral sheet misfit include a = 8.89O, and Dz = 0.193 Å, resulting in an interlayer spacing of 3.35 Å. The optical absorption spectrum of this V-rich muscovite shows absorption features at 427 and 609 nm that define a transmission window centered at 523 nm. These absorption features are consistent with those expected for V3+ in mica, but the 609 nm band has a slightly longer wavelength compared to low V-content micas.


In hand specimen, the mica appears as a thin green veins of mica flakes.

 hand specimen  
hand specimen

The optical spectrum arises from V3+.

Austria



Chemical Composition
Vanadian muscovite from Amstall:

SiO2         44.15
Al2O3        26.10
V2O3         11.35
Cr2O3         1.36
MgO           1.11
Na2O          0.31
K2O          10.45
H2O*          4.31
 Sum          99.15
* Calculated