Origin of Water in Mantle Eclogites from the V. Grib Kimberlite Pipe, NW Russia

The water content in the garnet and clinopyroxene in the mantle eclogites from the V. Grib kimberlite pipe (Arkhangelsk Diamondiferous Province, NW Russia) was analysed using Fourier transform infrared spectrometry. The results show that all clinopyroxene grains contained structural water at concentrations of 39 to 247 ppm, whereas two garnet samples contained detectable water at concentrations of 211 and 337 ppm. The low-MgO eclogites with oceanic gabbro precursors contained significantly higher water concentrations in the omphacites (70–247 ppm) and whole rock (35–224 ppm) compared to those with oceanic basalt protoliths (49–73 ppm and 20–36 ppm, respectively). The incorporation of water into the clinopyroxene may be associated with vacancies at the M2 site, Al in the tetrahedral position, and the elements that filled the M2 site (mostly Na and Ca). The highest water content in the omphacite was detected in a nonmetasomatised sample and was assumed to represent residual water that survived during subduction. Other eclogite samples showed signs of modal and/or cryptic metasomatism and contained less water in the omphacites compared to the nonmetasomatised sample. The water content was heterogeneous within the eclogite section of the sampled lithospheric mantle. The lack of distinct and uniform correlations between the indices of eclogite modification and their water content indicated that the saturation with water was disturbed during their residence within the lithospheric mantle.

Luxembourgite, AgCuPbBi₄Se₈, a new mineral species from Bivels, Grand Duchy of Luxembourg

Luxembourgite, ideally AgCuPbBi4Se8, is a new selenide discovered at Bivels, Grand Duchy of Luxembourg. The mineral forms tiny fibres reaching 200 µm in length and 5 µm in diameter, which are deposited on dolomite crystals. Luxembourgite is grey, with a metallic lustre and without cleavage planes; its Mohs hardness is 3 and its calculated density is 8.00 g cm−3. Electron-microprobe analyses indicate an empirical formula Ag1.00(Cu0.82Ag0.20Fe0.01)Σ1.03Pb1.13Bi4.11(Se7.72S0.01)Σ7.73, calculated on the basis of 15 atoms per formula unit. A single-crystal structure refinement was performed to R1=0.0476, in the P21∕m space group, with a=13.002(1), b=4.1543(3), c=15.312(2) Å, β=108.92(1)∘, V=782.4(2) Å3, Z=2. The crystal structure is similar to that of litochlebite and watkinsonite and can be described as an alternation of two types of anionic layers: a pseudotetragonal layer four atoms thick and a pseudohexagonal layer that is one atom thick. In the pseudotetragonal layers the Bi1, Bi2 ,Bi3, Pb, and Ag1 atoms are localised, while the Cu2 and Bi4 atoms occur between the pseudotetragonal and the pseudohexagonal layers. Bi1, Bi2, and Bi3 atoms occur in weakly distorted octahedral sites, whereas Bi4 occurs in a distorted 7-coordinated site. Ag1 occupies a fairly regular octahedral site, Cu2 a tetrahedral position, and Pb occurs on a very distorted 8-coordinated site.

Origin of water in the mantle eclogites from the V. Grib kimberlite pipe, NW Russia

<p>The study of water content in the rock-forming minerals of mantle xenoliths, entrained in kimberlites, provides information about the water storage of the lithospheric mantle of ancient cratons. In mantle xenoliths, the water can be identified as several percentages by weight in hydrous minerals (e.g. phlogopite and amphibole) and up to 2000 ppm in nominally anhydrous minerals (NAMs; olivine, pyroxene, and garnet). Since the hydrous phases occur sporadically in mantle xenoliths, their NAMs reserve the main water content in the lithospheric mantle.</p><p>The water content in garnet and clinopyroxene from the mantle eclogites from the V. Grib kimberlite pipe (Arkhangelsk Diamondiferous Province, NW Russia) was analysed using Fourier transform infrared spectrometry. The studied samples are coarse-grained (grain sizes from 0.5–1.3 cm) bimineralic (garnet and clinopyroxene) eclogites with accessories of phlogopite, ilmenite, and rutile. The samples include high-MgO (three samples) and low-MgO (six samples) groups. The eclogites are interpreted as metamorphosed fragments of oceanic crustal rocks (basalt and gabbro for low-MgO eclogites and picritic/MgO basalt and troctolite for high-MgO eclogites) emplaced into the lithospheric mantle via a subduction event at 2.8 Ga. Based on pressure-temperature estimates (44–78 kbar; 940°C–1275°C), eclogites were transported by kimberlite from the range of depths of about 160 to >200 km.</p><p>The results show that all clinopyroxene grains contain structural water in the amount of 39 to 111 ppm, whereas only two garnet samples have detectable water in the amount of 211 and 337 ppm. The water incorporation into the clinopyroxene is mostly linked to M2 sites and aluminium in the tetrahedral position. The water content in the majority of eclogite clinopyroxene positively correlates with the jadeite component. The low-MgO eclogites with oceanic gabbro precursor contain significantly higher water concentrations in omphacites (70–111 ppm) and whole rock (35–224 ppm) compared to those with the oceanic basalt protolith (49–73 ppm and 20–36 ppm, respectively). The proposed observation is also confirmed by the negative correlations of water content in clinopyroxenes with a La/Yb ratio in clinopyroxene and WR water content versus the WR Yb concentration. The equilibrium pressure could be an additional factor that controls the water incorporation into the clinopyroxene of the high-MgO group.</p><p>Our results show that water content in the V. Grib pipe eclogites is not from the mantle metasomatism and therefore can reflect the water saturation of their protoliths. The eclogite portion of the lithospheric mantle beneath the V. Grib kimberlite pipe can have at least twice the water enrichment compared to peridotite sections, indicating that an Archean subduction event played an essential role in the water saturation of the mantle.</p><p>This work was supported by the Russian Science Foundation under grant no. 16-17-10067</p>

Electrochemical and structural properties of Ni(II)-alumina composites as an annealing temperature function

Alumina powders, pure and doped with nickel, were synthetized by sol-gel method and calcined at 500, 900 and 1100?C in order to obtain mesoporous structures with a high specific surface area, well adapTab. to catalytic application. The characterization of samples was performed by XRD, EPR spectroscopy and electrochemical impedance spectroscopy (EIS). XRD analysis showed that the addition of Ni2+, as well as the annealing temperature, affects the structural properties of the obtained composites. EPR analysis revealed the traces of Fe3+ impurities, the presence of oxy defects in alumina and Ni2+ in tetrahedral position for samples calcined at 1100?C. The impedance of the Nafion/alumina modified GCE depended on combined effect of porous structure and surface properties of alumina samples. The electrochemical behavior of a glassy carbon electrode modified with Ni (II)-doped aluminas was studied in 0.5 M NaOH solution, with and without methanol. The electrochemical activity of nickel-doped alumina composites was dictated by the amount of present NiO impurity.

2D-to-disguised 3D materials with built-in acid sites: H+-[Al]-RUB-18

Al3+ heteroions have been incorporated into a Na-RUB-18 framework through a post-synthesis procedure under hydrothermal conditions. Characterization by 27Al NMR showed that aluminum is in tetrahedral position; the acidity present in the layers of the SiO2-pillared H+-[Al]-RUB-18 was probed by in situ ethanol dehydration monitored by FTIR.

The studies of granitoids from the Sobótka region in light of theories of the origin of colour in minerals

The article presents the results of the studies of 19 feldspar-quartz raw materials samples, coming from deposits located in the Sobótka region, in light of four distinct physical theories explaining mechanisms for creating the colour of minerals. This is a successive stage of research carried out by the author on reasons for colour variation of samples after firing at 1200°C. This step encompassed a detailed chemical analysis for main and trace elements contents of all the investigated samples as well as Mössbauer studies of two of them. The chemical analysis reveals that the darkest samples are characterised by the highest contents of the following colouring compounds and elements: Fe2O3, MnO, Th, U, Ce, Nd, and V, accompanied by a relatively low amount of TiO2. The Mössbauer studies demonstrated the quantitative predominance of Fe2+over Fe3+in the sample of a relatively darker hue with a high Fe2O3content, while its spectra parameters suggest that Fe2+is located in octahedral coordination that can result in a cold blue tint. Cations Fe3+(located probably in the tetrahedral position) prevail in the other analysed sample that contain less Fe2O3and a relatively high content of TiO2, Ce, and Nd. This probably causes a warm, reddish shade of the sample. The above-mentioned observations and examinations lead to the finding that, at this stage of the investigations, the crystal field theory could be the best suited for the interpretation of colour of the studied samples. This formalism associates the colour origin with ions of the transition elements, some REE and actinides located in the structure of minerals, and their ability to selectively absorb visible light.

Refinement of cronstedtite-1M

The structure of cronstedtite-1Mwas refined using a crystal from Eisleben (Saxony-Anhalt, Germany). The space group isCm,a= 5.5033 (3),b= 9.5289 (6),c= 7.3328 (5) Å, β = 104.493 (7)°, composition (Fe2+2.461Fe3+0.539)(Si1.461Fe3+0.539)O5(OH)4,Z= 2. Despite diffusely streaked characteristic polytype reflections, the refinement converged toRobs= 0.0242 for 1117 independent reflections. SeparateRobsvalues of 0.0183 and 0.0553 were obtained for 415 subfamily and 702 characteristic reflections, respectively. The structure is built of one edge-sharing octahedral (Oc) and one corner-sharing tetrahedral (Tet) sheet forming the 1:1 layer by sharing apical corners of theTetsheet. Consecutive layers are shifted bya/3 of the hexagonal cell, the polytype belongs to the subfamily (Bailey's group) A. There are two octahedral sitesM1 (atm),M2 (in a general position) both fully occupied by Fe. Since theM2 octahedron is larger thanM1, theOcsheet ismeso-octahedral. TheTetsheet contains one tetrahedral position,T1, occupied by Si and Fe in the ratio 0.731:0.269 (9). The ring of tetrahedra is strongly ditrigonalized, α = +12.7°; Franzini type A. Of three H atoms localized, two are involved in hydrogen bonds, linking OH groups of theOcsheet with basal O atoms of theTetsheet. The basal O atoms (acceptors) of theTetsheet are rotated close to OH groups (donors) of theOcsheet of an adjacent layer in order to achieve reasonable lengths and geometries of hydrogen bonds. The structure is interpreted as an example of the order–disorder (OD) structure of more than one kind of layer with a very low degree of desymmetrization.

Ab-Initio Study of Neutral Indium Diffusion in Uniaxially- and Biaxially-Strained Silicon

In this paper, we present our ab-initio study on energy configurations, minimum energy path (MEP), and migration energy for neutral indium diffusion in a uniaxial and biaxial tensile strained {100} silicon layer. Our ab-initio calculation of the electronic structure allowed us to figure out transient atomistic configurations during the indium diffusion in strained silicon. We found that the lowest-energy structure (Ins – SiiTd) consists of indium sitting on a substitutional site while stabilizing a silicon self-interstitial in a nearby tetrahedral position. Our ab-initio calculation implied that the next lowest energy structure is IniTd, the interstitial indium at the tetrahedral position. We employed the nudged elastic band (NEB) method for estimating the MEP between the two structures. The NEB method allowed us to find that that diffusion pathway of neutral indium is kept unchanged in strained silicon while the migration energy of indium fluctuates in strained silicon.

Ab Initio Study with Transition State Theory (TST) for the Calculation of the Barrier Height of Migration Energy of Neutral Indium in Silicon

In this paper, we present ab-initio study on the energy configurations, minimum energy path (MEP), and migration energy of neutral indium atom during diffusion in silicon crystal. From the ab-initio calculation of electronic structure, we could figure out the transient atomistic configurations during the indium diffusion in silicon. We found that the lowest-energy structure (Ins + Sii Td) consists of indium sitting on a substitutional site for stabilizing a silicon self-interstitial in a nearby tetrahedral position. The second lowest-energy structure was found to be Ini Td, the interstitial indium at the tetrahedral position. We employed the climbing image nudged elastic band (CINEB) method for estimating the MEP between the two local energy minima and the migration energy of the neutral indium, and obtained the MEP of 0.79 eV.