Description: Calcium carbonate precipitation in sea ice is thought to potentially drive significant CO2 uptake by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO3 within sea ice, although it is hypothesized that high quantities of dissolved organic matter and/or phosphate (common in sea ice) may inhibit its formation. In this quantitative study of hydrous calcium carbonate as ikaite, sea ice cores and brine samples were collected from pack and land fast sea ice between September and December 2007 during two expeditions, one in the East Antarctic sector and the other off Terre Adélie. Samples were analysed for CaCO3, salinity, dissolved organic carbon/nitrogen, inorganic phosphate, and total alkalinity. No relationship between these parameters and CaCO3 precipitation was evident. Ikaite was found mostly in the uppermost layers of sea ice with maximum concentrations of up to 126 mg ikaite per litre melted sea ice being measured, although both the temporal and horizontal spatial distributions of ikaite were highly heterogeneous. The precipitate was also found in the snow on top of the sea ice at some of the sampling locations.

Description: Sulphur speciation in lazurites and products of their high-temperature annealing in air or under various buffers is studied using S 2p X-ray photoelectron spectroscopy (XPS) and S K-edge XANES spectroscopy. The XPS as a more surface sensitive technique gives for instance less information on sulphide in the samples with oxidized surfaces whereas XANES spectroscopy enables access to such species in the bulk structure. However, both methods clearly indicate sulphate and polysulphides as main constituents in the structural cages of lazurites. Additionally, the data show sulphur species, such as sulphite, which mainly occur in a near-surface form, thiosulphate, monosulphide, and elemental sulphur. The non-cubic (orthorhombic and triclinic) lazurites – rich in sulphide – are characterized by high contents of polysulphide anions, which make up more than 20 at% of the total S. The cubic variety with low to medium S/SO4 ratios contains less polysulphide species. The lower limit of polysulphide (primarily S3-) responsible for the blue colour of lazurite is ~0.4 at%. However, in some cases there is no explicit correlation between blue colour and polysulphide content. Two types of transformation of polysulphide are considered. With high access of O2 (fine grained powders) polysulphide may interact with sulphate anions to form sulphite ions, and in presence of thiosulphate, sulphate and elemental sulphur result. It appears to be the most probable mechanism for non-cubic lazurites rich in polysulphide. In the absence of access to air oxygen (in coarse grains), S3- can be transformed by the interaction with sulphate to thiosulphate and possibly to S2O-, or by disproportionation into S° and S2-. The formation of S° is rarely observable in natural lazurites. Additional anions can participate in the reactions of more abundant sulphate and polysulphide anions giving rise to the formation and degradation of colour centres. Structural modifications of lazurite show different anionic compositions in their cages and, hence cannot be considered polymorphs in the strict sense. They rather represent phases of variable compositions depending on temperature, SO2 fugacity, ordering and ratios of clusters containing Na and Ca. Modulations of the lazurite structure are possibly controlled by three types of clusters that are polysulphide, thiosulphate, and sulphate (nosean-type and haüyne-type), whose compositions and ratios depend on external (temperature, redox conditions) and internal factors (sulphur content, Na/Ca ratio).

Description: We present the results of an investigation of tailing ponds and contaminated soils at five antimony deposits in Slovakia, Pezinok, Dúbrava, Medzibrod, Čučma, and Poproč. With the exception of Poproč, all primary mineralization contained abundant carbonates; the sites studied are examples of neutral mine drainage. The Fe–As–Sb-rich products of weathering were studied in 250 samples of tailings and also in contaminated soils for comparison. They were examined by means of 2500 electron-microprobe (EMP) and 500 micro-X-ray diffraction (μ-XRD) analyses. The primary focus of this work is the incorporation of the metalloids Sb and As into (poorly) crystalline authigenic phases, not their association with mineral surfaces. The EMP analyses define a densely populated field in a triangular Fe–Sb–As diagram. Compositions along the entire Fe–Sb edge are common; many of them lie near the Fe apex, with an (As + Sb)/(Fe + As + Sb) value not exceeding 0.3. Oxidation-induced rims on arsenopyrite mostly consists of X-ray-amorphous hydrous ferric oxides (HFO) with average As and Sb contents equal to 13.9 and 5.69 wt%, respectively. The rims developed on pyrite mostly consist of goethite or a mixture of goethite and HFO, which acts as effective sorbents of As, Sb, Ca, Si and Cu. Among the grains without relics of primary sulfides, HFO with variable concentrations of As, Sb is common. The most common secondary mineral at all sites is goethite, with average As and Sb contents of 1.33 and 3.93 wt%, respectively. A very common Sb-bearing secondary phase at all studied localities is tripuhyite (FeSbO4). Calcium antimonates with the pyrochlore structure are typical of environments rich in Ca. Simple secondary Sb oxides such as cervantite and sénarmontite were observed each in only one soil sample. Beudantite was identified in a few samples with a higher Pb content. In one sample, a porous secondary oxide rich in Pb and As was identified as clinomimetite.

Description: Calcium carbonate precipitation in sea ice is thought to potentially drive significant CO2 uptake by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO3 within sea ice, although it is hypothesized that high quantities of dissolved organic matter and/or phosphate (common in sea ice) may inhibit its formation. In this quantitative study of hydrous calcium carbonate as ikaite, sea ice cores and brine samples were collected from pack and land fast sea ice between September and December 2007 during two expeditions, one in the East Antarctic sector and the other off Terre Ade´lie. Samples were analysed for CaCO3, salinity, dissolved organic carbon/nitrogen, inorganic phosphate, and total alkalinity. No relationship between these parameters and CaCO3 precipitation was evident. Ikaite was found mostly in the uppermost layers of sea ice with maximum concentrations of up to 126 mg ikaite per litre melted sea ice being measured, although both the temporal and horizontal spatial distributions of ikaite were highly heterogeneous. The precipitate was also found in the snow on top of the sea ice at some of the sampling locations.

Description: Projectile–target interactions as a result of a large bolide impact are important issues, as abundant extraterrestrial material has been delivered to the Earth throughout its history. Here, we report results of shock-recovery experiments with a magnetite-quartz target rock positioned in an ARMCO iron container. Petrography, synchrotron-assisted X-ray powder diffraction, and micro-chemical analysis confirm the appearance of wüstite, fayalite, and iron in targets subjected to 30 GPa. The newly formed mineral phases occur along shock veins and melt pockets within the magnetite-quartz aggregates, as well as along intergranular fractures. We suggest that iron melt formed locally at the contact between ARMCO container and target, and intruded the sample causing melt corrosion at the rims of intensely fractured magnetite and quartz. The strongly reducing iron melt, in the form of μm-sized droplets, caused mainly a diffusion rim of wüstite with minor melt corrosion around magnetite. In contact with quartz, iron reacted to form an iron-enriched silicate melt, from which fayalite crystallized rapidly as dendritic grains. The temperatures required for these transformations are estimated between 1200 and 1600 °C, indicating extreme local temperature spikes during the 30 GPa shock pressure experiments.