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

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) Å, 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 Å. Structural distortions include α = 8.89° and Δz = 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 V^(3+) in mica, but the 609 nm band has a slightly longer wavelength than in low-V micas

Pb remobilization by bacterially mediated dissolution of pyromorphite Pb_{5}(PO_{4})_{3}Cl in presence of phosphate-solubilizing Pseudomonas putida

Remediation of lead (Pb)-contaminated sites with phosphate amendments is one of the best studied and cost-effective methods for in situ immobilization. In this treatment, a very stable mineral, pyromorphite Pb(5)(PO(4))(3)Cl, is formed. Several studies propose to improve this treatment method with the addition of phosphate-solubilizing bacteria (PSB). The effect of bacteria on solubilization of pyromorphite is unknown. In this study, the effect of the soil microorganisms on the stability of pyromorphite Pb(5)(PO(4))(3)Cl has been investigated in a set of batch solution experiments. The mineral was reacted with Pseudomonas putida, a common soil microorganism. Dissolution of pyromorphite was enhanced by the presence of P. putida, resulting in an elevated Pb concentration in the solution. This occurred even when the bacteria were provided with an additional source of phosphate in the solution. Pyromorphite has been shown to be a potential source of nutrient phosphorus for common soil bacteria. Thus, the use of PSB in remediation treatments of Pb contaminated sites may have adverse long-term impacts on Pb immobilization. Conscious phosphate management is suggested for long-term sustainability of the in situ Pb immobilization by pyromorphite formation

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

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) Å, 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 Å. Structural distortions include α = 8.89° and Δz = 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 V^(3+) in mica, but the 609 nm band has a slightly longer wavelength than in low-V micas

Multiple length scale growth spirals on metamorphic graphite {001} surfaces studied by atomic force microscopy

The microtopography of {001} surfaces on single crystals of graphite from a Neoproterozoic marble of the Swakop group, near Wlotzkas Baken, western Namibia, has been studied using differential interference contrast (DIC) microscopy and atomic force microscopy (AFM). A unique aspect of the observed surface microtopography is the presence of growth spirals and hillocks on three different length scales. The largest spirals are polygonized and can be seen without magnification. Steps on this feature are roughly 4 μm high and 90 μm apart. The second-order features are hexagonal growth hillocks with an average step height of 1.5 nm and total lateral dimensions of 5–40 μm. The apex of these hillocks coincides directly with the apex of reentrants in the macrosteps of the large spiral. Morphology suggests the formation of these polygonized hillocks by some mechanism other than simple spiral growth. We speculate that these features may be due to pinning of the macrostep by impurities and subsequent formation of the second-order hillocks. The third length-scale features are spirals found on terraces forming the vicinal faces of the second-order hillocks. These spirals have steps that are 6.7 Å high (unit-cell length along [001]) and an average step spacing of 900 Å. These double-layer steps also show some regions with partial step separation into 3.3 Å high monolayer steps. The observed microtopographic features give us insight into the conditions in, and mechanisms by which these graphite crystals formed during carbonate metamorphism. Crystal growth, unrestricted by the surrounding calcite, was from a fluid phase at low graphite supersaturation and was dominated by the spiral growth mechanism. Comparison with theoretical and simulation studies suggests a critical radius for two-dimensional nucleation on the (001) surface on the order of 100 Å