Alla M. Logvinova

Nanometre-sized mineral and fluid inclusions in cloudy Siberian diamonds: new insights on diamond formation

Nanometre-sized isolated inclusions have been studied in four cloudy octahedral diamonds from the Internatsionalnaya and one from the Yubileynaya mines (Yakutia). Transmission electron microscopy (TEM) techniques such as electron diffraction, analytical electron microscopy (AEM), electron energy-loss spectroscopy (EELS) and high-resolution electron microscopy (HREM) were applied as well as line scan and elemental mapping of the samples. All crystals exhibit octahedral external habit with opaque central cuboid cores that contain numerous nano-inclusions. All nano-inclusions in the size range between 30 and 800 nm reflect the diamond habit and are considered primary, syngenetic to host diamond. They are composed of multi-phase assemblages, which include solid phases (silicates, oxides, carbonates), brines (halides), and fluid bubbles. These inclusions are relatively homogeneous in composition and contain distinguishable crystalline and fluid phases. Al-bearing high-Mg silicate, dolomite, Ba-Sr carbonate, phlogopite, ilmenite, ferropericlase, apatite, magnetite, K-Fe sulfides (djerfisherite?) and kyanite have been identified as crystalline mineral phases by electron diffraction patterns, except the Ba-Sr carbonate. Several phases, including CaF 2 and clinohumite-like phases, have never been reported as inclusions in diamond. The halide phase was KCl. Bubbles contained high K, Cl, O, P and less S, Ba, Si, Ti components. Carbonates were identified in TEM foils from all studied diamonds. They occur in all assemblages with silicates, oxides, and sulfides and show a general enrichment in incompatible elements such as Sr and Ba. Some elemental variations may be explained by fractional crystallization of fluid/melt or mixing of fluids with different compositions (carbonatitic, hydrous-silicic, brines).

Shulamitite Ca3TiFe3+AlO8 – a new perovskite-related mineral from Hatrurim Basin, Israel

Shulamitite, ideally Ca 3 TiFe 3+ AlO 8 , is a mineral intermediate between perovskite CaTiO 3 and brownmillerite Ca 2 (Fe,Al) 2 O 5 . It was discovered as a major mineral in a high-temperature larnite-mayenite rock from the Hatrurim Basin, Israel. Shulamitite is associated with larnite, F-rich mayenite, Cr-containing spinel, ye9elimite, fluorapatite, and magnesioferrite, and retrograde phases (portlandite, hematite, hillebrandite, afwillite, foshagite and katoite). The mineral forms reddish brown subhedral grains or prismatic platelets up to 200 μm and intergrowths up to 500 μm. The empirical formula of the holotype shulamitite (mean of 73 analyses) is (Ca 2.992 Sr 0.007 LREE 0.007 )(Ti 0.981 Zr 0.014 Nb 0.001 )(Fe 3+ 0.947 Mg 0.022 Cr 0.012 Fe 2+ 0.012 Mn 0.001 )(Al 0.658 Fe 3+ 0.288 Si 0.054 )O 8 . The X-ray diffraction powder-pattern (Mo Kα -radiation) shows the strongest lines {d [A]( I obs )} at: 2.677(100), 2.755(40), 1.940(40), 11.12(19), 1.585(17), 1.842(16), 1.559(16), 3.89 (13), 1.527(13). The unit-cell parameters and space group are: a = 5.4200(6), b = 11.064(1), c = 5.5383(7) A, V= 332.12(1) A 3 , Pmma, Z = 2. The calculated density is 3.84 g/cm 3 . The crystal structure of shulamitite has been refined from X-ray single-crystal data to R 1 = 0.029 %. No partitioning among octahedral sites was found for Ti and Fe 3+ in the structure of shulamitite, these cations are randomly distributed among all octahedra indicating an example of “valency-imposed double site occupancy”. The strong bands in the Raman spectrum of shulamitite are at: 238,250, 388,561, and 742 cm −1 . Shulamitite from the Hatrurim Basin crystallized under combustion metamorphism conditions characterized by very high temperatures (1150−1170 °C) and low pressures (high- T -region of the spurrite-merwinite facies). Chemical data for shulamitite and its Fe-analog from other metacarbonate occurrences (natural and anthropogenic) are given here.

Structural parameters of chromite included in diamond and kimberlites from Siberia: A new tool for discriminating ultramafic source

Abstract Siberian chromite included in diamond, kimberlite, and spinel peridotite as well as Cr-spinel from garnet-spinel peridotite have been studied by single-crystal X-ray diffraction and electron microprobe analysis. Cell edges and oxygen positional parameters, u, of chromite in diamond and in kimberlite are comparable (cell edge, 8.3249-8.3390 Å; u, 0.26175-0.26213). The structural parameters of chromite in the spinel peridotite are similar to those of chromite grains from ophiolitic complexes, and those of Cr-spinel from garnet-spinel peridotite are comparable to those of Cr-spinel in lherzolitic mantle xenoliths. With the exception of the chromite in garnet-spinel peridotite, all analyzed spinels have a high Cr content. Recasting the chemical analyses according to spinel stoichiometry reveals negligible or no Fe3+. Chrome spinel may be present in heavy concentrates derived from serpentinized mafic and ultramafic rocks as the sole surviving primary mineral and, as such, their particular structural and chemical parameters may represent a new prospecting tool for discriminating the ultramafic source.

Geochemistry of Multiple Diamond Inclusions of Harzburgitic Garnets as Examined In Situ

Komsomolskaya high-Cr, harzburgitic-garnet, multiple diamond inclusions exhibit extremely variable and unusual LREE patterns. The high Cr2O3 contents of these diamond inclusions are exceptional, and indicate a possible genesis intermediate between that of harzburgitic and lherzolitic garnets. Both the major- and trace-element compositions of the garnet inclusions within a single diamond are unique, illustrating that each diamond has experienced a distinctly different chemical environment during its formation, in some cases even varying significantly during different episodes of growth within one diamond. Results of this study emphasize that such diamonds have been subjected to extreme changes in P-T-X conditions during their complex growth histories.

Eskolaite associated with diamond from the Udachnaya kimberlite pipe, Yakutia, Russia

Abstract The mineral eskolaite (Cr2O3) has been discovered in association with natural diamond from the Udachnaya pipe in Yakutia, where it is intergrown with an octahedral diamond, mostly as an inclusion in the diamond, but also exposed at its surface. A detailed study was performed on fragments extracted from the outer surface of the diamond, using single-crystal X-ray diffraction (XRD), high-resolution electron microscopy (HRTEM), analytical electron microscopy (AEM), including line-scan and elemental-mapping, EMP, and SIMS. These applied techniques confirmed the nature of the eskolaite with 86.8 wt% Cr2O3 and notable impurities of TiO2 (3.99 wt%), Al2O3 (2.00 wt%), Fe2O3 (5.83 wt%), and MgO (1.11 wt%). Trace elements, including V (4900 ppm), Mn (129 ppm), Zr (56 ppm), and Nb (32 ppm) were also detected. The entire range of REE is just at or below the limits of detection. A small picrochromite inclusion (XMg 81.2; YCr 94.7) was detected in the eskolaite; its chemistry is typical of chromite diamond inclusions. It also contains minute inclusions of perovskite, corundum, and an unidentified Ti-phase. Nano-sized cavities in picrochromite were determined to consist of carbonate and quench products, including Si, Mg, Ca, P, K, and Cl. This may represent relics of the diamond-forming metasomatic fluids. The eskolaite, containing a picrochromite inclusion, was formed at high pressure within the diamond stability field from C-O-H-bearing fluids containing Ca, K, Cl, P, and possibly even peridotitic (U-type) oxides and silicates.

A micro-Mössbauer study of chromites included in diamond and other mantle-related rocks

Oxygen fugacity (

Unique Compositional Peculiarities of Olivine Phenocrysts from the Post Flood Basalt Diamondiferous Malokuonapskaya Kimberlite Pipe, Yakutia

f_{{{\text{O}}_{ 2} }}

Carbonate–Silicate–Sulfide Polyphase Inclusion in Diamond from the Komsomolskaya Kimberlite Pipe, Yakutia

fO2) is a fundamental but little known intensive variable in mantle processes. It influences the P/T position of a mantle solidus and the composition of mantle-derived melts and fluids and constrains mantle-core equilibria and a number of geophysical properties of the mantle. An important source of information on oxidation states is the ferric–ferrous iron ratio in mantle spinels. Since the magnetite component is low in mantle spinels, normal analytical errors translate into considerable