Orthorhombic lazurite from the Tultui deposit in the Baikal region

A lazurite sample taken from the Tultui deposits in the Baikal region has been studied using petrographic examination, X-ray diffraction, and local X-ray spectroscopy (electron microprobe). It is established that the line of the basic cell in the X-ray diffraction pattern of the orthorhombic lazurite is widened, so the unit-cell parameters should be recalculated from the interlayer distances of the superstructural reflections. The chemical compositions and unit-cell parameters of the lazurites from the Baikal region and the Pamirs are different. Two schemes of the chemical substitutions of atoms in the mineral are assumed: (1) the hauyne cluster [Na₃CaSO₄]³⁺ is replaced with a sodalite cluster [Na₄Cl]³⁺, and (2) two hauyne clusters 2[Na₃CaSO₄]³⁺ are substituted by nosean clusters [Na₄SO₄]⁺ and [Na₄H₂O]⁴⁺ with retention of the total charge. The increase in the Na and Cl contents in the orthorhombic lazurite is accompanied by a decrease in the unit-cell dimensions. Orthorhombic lazurites from the southern Baikal region and the southwestern Pamirs were formed in apocarbonate (apocalciphyre) metasomatic rocks at a lower temperature than pyroxene, afghanite, and cubic lazurite.     

Fenestral limestones: Specific features of late Devonian seas in the Timan-northern Ural region

The article is dedicated to the lithological-paleoecological analysis of Upper Devonian fenestral limestones from different areas of the Timan-northern Ural region, which reflect paleogeographic settings from the coastal zone to the marginal part of the shelf. It is established that their main structural elements are represented by fenestrae, peloids, calcispheres, and occasional microzoo- and phytobenthos remains. The presence of a dark micritic envelope on calcispheres is their specific textural feature. The envelope of calcispheres represents mineralized vegetable mucus, which reflects their planktonic type of dwelling. These structures include representatives of radiolarian skeletons, Charophyceae and Chlorophyceae algae, and foraminiferal tests. The trophic system consists of five levels. Carbonate sediments accumulated in relatively shallowwater and lagoonal settings occupied mostly by tidal and shallow-water subtidal microbial mats. In these lagoons, intermittently limited circulation stimulated the formation of anoxic conditions in bottom waters. Development of anoxic conditions in the bottom water layer, sulfate reduction, and freshwater influence determined the formation of a specific paleocoenosis of fenestral limestones, which could not form biogenic frameworks.     

Vladimirivanovite, Na6Ca2[Al6Si6O24](SO4,S3,S2,Cl)2 · H2O, a new mineral of sodalite group

The results of an examination of vladimirivanovite, a new mineral of the sodalite group, found at the Tultui deposit in the Baikal region are discussed. The mineral occurs in the form of outer rims (0.01–3 mm thick) of lazurite, elongated segregations without faced crystals (0.2 to 3–4 mm in size; less frequently, 4 × 12–15 × 20 mm), and rare veinlets (up to 5 mm) hosted in calciphyre and marble. Vladimirivanovite is irregular and patchy dark blue. The mineral is brittle; on average, the microhardness VHN is 522–604, 575 kg/mm²; and the Mohs hardness is 5.0–5.5. The measured and calculated densities are 2.48(3) and 2.436 g/cm³, respectively. Vladimirivanovite is optically biaxial; 2V _meas = 63(±1)°, 2V _calc = 66.2°; the refractive indices are α = 1.502–1.507 (±0.002), N _m = 1.509–1.514 (±0.002), and N _g = 1.512–1.517 (±0.002). The chemical composition is as follows, wt %: 32.59 SiO₂, 27.39 Al₂O₃, 7.66 CaO, 17.74 Na₂O, 11.37 SO₃, 1.94 S, 0.12 Cl, and 1.0 H₂O; total is 99.62. The empirical formula calculated based on (Si + Al) = 12 with sulfide sulfur determined from the charge balance is Na_6.36Ca_1.52(Si_6.03Al_5.97)_Σ12O_23.99(SO₄)_1.58(S₃)_0.17(S₂)_0.08 · Cl_0.04 · 0.62H₂O; the idealized formula is Na₆Ca₂[Al₆Si₆O₂₄](SO₄,S₃,S₂,Cl)₂ · H₂O. The new mineral is orthorhombic, space group Pnaa; the unit-cell dimensions are a = 9.066, b = 12.851, c = 38.558 Å, V = 4492 ų, and Z = 6. The strongest reflections in the X-ray powder diffraction pattern (dÅ—I[hkl]) are: 6.61–5[015], 6.43–11[020, 006], 3.71–100[119, 133], 2.623–30[20.12, 240], 2.273–6[04.12], 2.141–14[159, 13.15], 1.783–9[06.12, 04.18], and 1.606–6[080, 00.24]. The crystal structure has been solved with a single crystal. The mineral was named in memoriam of Vladimir Georgievich Ivanov (1947–2002), Russian mineralogist and geochemist. The type material of the mineral is deposited at the Mineralogical Museum of St. Petersburg State University, St. Petersburg, Russia.     

Sulfur-Bearing Sodalite,Hackmanite, in Alkaline Pegmatites of the Inagli Massif (Aldan Shield): Crystal Chemistry,Photochromism, and Luminescence

Geology of Ore Deposits - Abstract—Sulfur-containing sodalite, hackmanite, has been found for the first time in alkaline pegmatites of the Inagli alkaline–ultramafic massif, South...     

Structure and modeling of disorder in miserite from the Murun (Russia) and Dara-i-Pioz (Tajikistan) massifs

The structure, structural disorder and chemistry of miserite from the charoite-bearing rocks of the Murun massif (Russia) and from alkaline-syenite pegmatitic rocks of the Dara-i-Pioz massif (Tajikistan) were investigated employing a combination of electron microprobe, single crystal diffraction and micro-Fourier transform infrared spectroscopy analysis. Chemical analysis of the sample investigated by X-ray diffraction evidenced that Dara-i-Pioz miserite has a greater REE concentration than Murun miserite (~0.22 vs. 0.05 apfu, respectively) and also contains Y (0.14 apfu), which is absent in Murun miserite. The occurrence of a band at about 1,600 cm^?1 testified to the presence of H₂O in miserite at hand. Structural analyses yielded average cell parameters of a = 10.092, b = 16.016, c = 7.356 Å, α = 96.60°, β = 111.27° and γ = 76.34°. Anisotropic structural refinement in space group P $\bar{1}$ converged at similar values for the analyzed samples (R ~3.4, R _w ~3.8 %). An interesting feature shown by both the miserite specimen is the presence, revealed by difference Fourier analysis, of a disordered part of the structure. This turned out to be due to the flipping of the tetrahedra belonging to the isolated [Si₂O₇]^6? diorthogroups, one of the two radicals (the other is [Si₁₂O₃₀]^12?) characterizing the miserite structure. The sixfold and seven-vertex Ca polyhedra linked to the inverted diorthogroups show variation in coordination number with respect to those of the ordered structure.