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Farbige Gläser aus Verhüttungsschlacken dienten bis in die Neuzeit in Kunst und Architektur als Ersatz für teurere Edelsteine und mineralische Pigmente. Wie die Farben der Gläser zustande kamen, war lange unklar. Elektronenmikroskopie und Röntgenspektrometrie haben das Rätsel nun entschlüsselt.

Ellinaite, a natural analog of the post-spinel phase β-CaCr2O4, was discovered at the Hatrurim Basin, Hatrurim pyrometamorphic formation (the Mottled Zone), Israel, and in an inclusion within the super-deep diamond collected at the placer of the Sorriso River, Juína kimberlite field, Brazil. Ellinaite at the Hatrurim Basin is confined to a reduced rankinite–gehlenite paralava, where it occurs as subhedral grains up to 30 µm in association with gehlenite, rankinite and pyrrhotite or forms the rims overgrowing zoned chromite–magnesiochromite. The empirical formula of the Hatrurim sample is (Ca0.960Fe0.0162+Na0.012Mg0.003)0.992(Cr1.731V0.1833+Ti0.0683+Al0.023Ti0.0034+)2.008O4. The mineral crystallizes in the orthorhombic system, space group Pnma, unit-cell parameters refined from X-ray single-crystal data: a 8.868(9), b 2.885(3), c 10.355(11) Å, V 264.9(5) Å3 and Z=4. The crystal structure of ellinaite from the Hatrurim Basin has been solved and refined to R1=0.0588 based on 388 independent observed reflections. Ellinaite in the Juína diamond occurs within the micron-sized polyphase inclusion in association with ferropericlase, magnesioferrite, orthorhombic MgCr2O4, unidentified iron carbide and graphite. Its empirical formula is Ca1.07(Cr1.71Fe0.063+V0.06Ti0.03Al0.03Mg0.02Mn0.02)Σ1.93O4. The unit-cell parameters obtained from HRTEM data are as follows: space group Pnma, a 9.017, b 2.874 Å, c 10.170 Å, V 263.55 Å3, Z=4. Ellinaite belongs to a group of natural tunnel-structured oxides of the general formula AB2O4, the so-called post-spinel minerals: marokite CaMn2O4, xieite FeCr2O4, harmunite CaFe2O4, wernerkrauseite CaFe23+Mn4+O6, chenmingite FeCr2O4, maohokite MgFe2O4 and tschaunerite Fe(FeTi)O4. The mineral from both occurrences seems to be crystallized under highly reduced conditions at high temperatures (>1000 ∘C), but under different pressure: near-surface (Hatrurim Basin) and lower mantle (Juína diamond).

Ophiolitic podiform chromitites from Phanerozoic orogens have been shown to preserve a wealth of textures and inclusions that, in some way, trace earlier episodes of subduction and crust mantle interactions, including traces of the major elements Carbon – Hydrogen – Oxygen – Nitrogen – Sulfur - Phosphorous (CHONSP) needed to sustain a habitable planet. Here, we report the first comprehensive documentation of the textures and inclusions of an Archean (circa 2.55 Ga) podiform chromitite from an orogenic ophiolitic mélange in China, recording an ancient CHONSP cycle, during the start of Earth’s transition from a reducing to an oxidized surface environment during the Great Oxidation Event, providing evidence for a dynamic link of Archean-Paleoproterzoic tectonics, and creation of a habitable planet. The composition of the inclusions indicates profound mixing of crustal and mantle sources in the Archean, and the textures show that they were included in chromite grains that began their growth as spherules that aggregated from immiscible silicate-oxide melts near the mantle transition zone at temperatures above 1900°C, forming host chenmingite at 14 GPa, or about 410 km. The melts then protruded upward in an extensional fore-arc, reacting with host harzburgites, progressively including a wide assortment of previously subducted mineral and rock fragments as xenocrysts and xenoliths in the progressively crystallizing chromite. The inclusions include ultra-high pressure TiO2 (II) stable at 7.5 GPa (or about 270 km) at 1000 °C, plus carbonates, hydrous and nominally anhydrous silicates, oxides, base metals, platinum group minerals, previously unidentified OsIrS, and pure carbon as graphite polymers. As the chromite-bearing melts rose further, they finally crystallized near the crust-mantle boundary of a circa 2.55-billion-year-old fore-arc ophiolite, that was soon, by the dawn of the Paleoproterozoic, involved in an arc/continent collision that emplaced the mantle rocks onto a fragment of older continental crust. This early record of inclusion of previously deeply subducted minerals in an orogenic ophiolitic podiform chromitite shows that plate tectonics and subduction have regulated crust-mantle interactions and the life-sustaining deep CHONSP cycles on Earth at least since the Archean, consistent with numerical models showing how C-O-H cycling related to subduction led to a rapid oxygenation of the mantle in the late Archean.

Working with Hamiltonians from chiral effective field theory, we develop a novel framework for describing arbitrary deformed medium-mass nuclei by combining the in-medium similarity renormalization group with the generator coordinate method. The approach leverages the ability of the first method to capture dynamic correlations and the second to include collective correlations without violating symmetries. We use our scheme to compute the matrix element that governs the neutrinoless double beta decay of $^{48}$Ca to $^{48}$Ti, and find it to have the value $0.61$, near or below the predictions of most phenomenological methods. The result opens the door to ab initio calculations of the matrix elements for the decay of heavier nuclei such as $^{76}$Ge, $^{130}$Te, and $^{136}$Xe., 6 pages, 4 figures and 1 table. supplementary material included. version to be published

Rates of mineral reactions are controlled by two major factors: surface kinetics and element transport. Dissolution and precipitation of minerals in the presence of a hydrous fluid is assumed to occur predominantly by hydrolysis of the outermost charged monolayers of the reacting crystal and subsequent incorporation of atoms from ionic solutions into favorable sites at the product surface. Element transport during mineral reactions is commonly thought to occur via ionic solutions with the mineral solubility in the coexisting fluid being a rate limiting factor. Here we show in high-pressure/low temperature rocks that an alkali-Al-Si-rich amorphous material forms directly by depolymerization of the crystal lattice. Depolymerization starts along grain or phase boundaries, dislocation cores in the crystal lattice or lattice defects in general that serve as element exchange pathways and are also sites of porosity formation. High hydrogen concentrations in such dislocation cores within nominally anhydrous pyroxene has been confirmed by Nano-SIMS measurements and indicates hydrolysis and recrystallization within mineral grains. Element transfer in the alkali-Al-Si-rich amorphous material is thermodynamically decoupled from ionic solutions and therefore enables significantly higher element transport rates than previously thought. The resulting amorphous material occupies large volumes in an interconnected porosity network which has been documented in 3D imaging. Precipitation of product minerals occurs directly by repolymerization of the amorphous material at the product surface. This new dissolution-reprecipitation mechanism has major implications for the role of mineral reactions during geophysical and geochemical processes in the dynamic Earth.

Carbonatites are common in continental settings but have, so far, only been identified at two oceanic localities, the Cape Verde and Canary Islands, both resting on > 130 Ma old, thick and cool oceanic crust. Here, we report on the first carbonatites observed in a hotter and younger mid-ocean setting, occuring as xenolithic fragments in nephelinitic tuffs at Salt Lake Crater (SLC), Oahu, Hawaii. The existence of Hawaiian carbonatites has been hypothesized before from various lines of evidence: (1) production of carbonatitic melts require carbonate in their source1; (2) diamond and SiC-bearing SLC xenoliths indicate mixed carbonatitic-silicic metasomatic agents in the sub-Hawaiian mantle 2 and (3) so do trace element compositions of Niihau 3 and SLC 4 post-erosional magmas. The potential role of mantle carbonatites on assimilation-fueled ascent of kimberlitic magmas has been the subject of two recent experimental studies 5,6. For experimental reasons, both these experiments failed to reproduce conditions prevailing at mantle depth by applying either too low pressure of 1 atm 5 or using Na2 CO3 as a substitute for Ca-Mg carbonate 5,6. Here, we show the CO2 producing reaction CaCO3+ Opx -> Cpx + CO2 “caught in the act” and in-situ in sub-Hawaiian carbonatite bearing xenoliths. We document the reaction by means of SEM and TEM analyses and discuss the carbonatites’ isotope composition for C, O and Sr with respect to their parentage.