Vanadium-rich Muscovite from Austria: Crystal Structure, Chemical Analysis, and Spectroscopic Investigations

Abstract

The crystal structure of a green, transparent, vanadium-rich muscovite-2M_1 (V_2O_3 = 11.35 wt.%, one of the highest amounts reported to date in muscovite) with the optimized formula (K_(0.94)Na_(0.06))M2(Al_(1.20)V^(3+)_(0.61)Mg_(0.12)Cr^(3+)_(0.07))T1(Si^(1.54)Al_(0.46))T2(Si_(1.54)Al_(0.46))O_(10)(OH)_2 and space group C2/c, a 5.2255(6), b 9.0704(10), c 20.0321(21) A, β 95.773(2)°, Z = 4 has been refined to R = 6.97% for 1070 unique reflections (MoKα). This muscovite, which occurs in small quartz veins in graphite schist from Weinberg mountain, near the village of Amstall, Lower Austria, is distinctly low in Cr (Cr_2O_3 ∼1.4 wt.%) and Mg (MgO ∼1.1 wt.%); Fe, Mn, and Ti are below detection limit. All octahedral cations occupy the M2 site, and the average octahedral bond (M2–O) distance is 1.953 A. Structural distortions include α = 8.89° and Δz = 0.193 A, resulting in an interlayer spacing of 3.35 A. 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 V^(3+) in mica, but the 609 nm band has a slightly longer wavelength than in low-V micas.