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In MgSiO SB 3 sb glass, the average Mg-O bond length is more-or-less constant with pressure up to ~10 GPa [from 2.051(30) at 0 GPa to 2.062(30) at 9.8 GPa] and then turns downward with further pressure increases. Keywords: MgSiO3 glass; high pressure; structural modification; Raman spectroscopy; Brillouin spectroscopy; X-ray scattering EN MgSiO3 glass high pressure structural modification Raman spectroscopy Brillouin spectroscopy X-ray scattering 1313 1324 12 07/05/22 20220701 NES 220701 Introduction The present day Earth possesses a crust composed of low-density minerals enriched in incompatible lithophile elements and a high-density metallic core beneath the rocky mantle, indicating that our planet is a well-differentiated body. Indeed, between 10 and 30 GPa, the average Mg-O distances in MgSiO SB 3 sb and Mg SB 2 sb SiO SB 4 sb glasses follow roughly the same trend, with r SB (Mg-O) sb in MgSiO SB 3 sb glass somewhat larger, suggesting that at the same pressure Mg-O polyhedra in Mg SB 2 sb SiO SB 4 sb glass are under more compression. The initial compression ( I K i SB T sb 0) is dominated by the response of Mg-O polyhedra, which, at >15 GPa, help transmit pressure onto the SiO SB 4 sb tetrahedra, causing the Si-O coordination number to increase at a similar rate to that in SiO SB 2 sb glass, with significantly increased rigidity. Figure 2a summarizes the structural modifications by compression based on Raman mode changes: (1) a discontinuity of Raman peaks at ~900 and ~512 cm SP -1 sp at ~8 GPa; (2) the emergence of a new peak at ~600 cm SP -1 sp at ~8 GPa; (3) a discontinuity of the 1096 cm SP -1 sp peak at ~20 GPa; (4) the emergence of a new peak at ~360 cm SP -1 sp at 20 GPa; and (5) the emergence of a new peak at 860 cm SP -1 sp at 40 GPa. [Extracted from the article]

Within this work, we present the first true three‐dimensional (3D) analysis of chondrule size. Knowledge about the physical properties of chondrules is important for validating astrophysical theories concerning chondrule formation and their aggregation into the chondritic meteorites (known as chondrites) that contain them. The classification of chondrites into chemical groups also relies on chondrule properties, including their dimensions. Within this work, we quantify the diameters of chondrules in five ordinary chondrites (OCs; comprised of the H, L, and LL chondrites) and one low‐iron enstatite (EL) chondrite. To extract the chondrule size data, we use x‐ray computed microtomography to image small (~1–2 cm3) chondrite samples followed by manual digital segmentation to isolate chondrules within the volumes or subvolumes. Our data yield true 3D results without stereographic corrections necessary for two‐dimensional (2D) or petrographic thin section‐based determinations of chondrule sizes. Our results are completely novel, but are consistent with previous surface analysis (2D) data for OCs. Within our OC chondrule diameter data, we find the trend of mean chondrule diameters increasing in the order H < L < LL. We also present the first detailed EL chondrite chondrule size‐frequency distribution. Finally, we examine the shapes and collective orientations of the chondrules within the chondrites and show that chondrite petrofabrics can be explored with our methodology. Chondrule shape‐preferred orientations are identical to the orientations of the metal and sulfide grains in the chondrites and this is likely due to impact‐related compaction. Highlights: We present a first true three‐dimensional analysis of chondrule size.Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites.We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution.We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology. [ABSTRACT FROM AUTHOR]

Spatially resolved absorption spectroscopy (XAS) was used to study the in situ chemical speciation of uranium (U). Qualitative information on U-bonding environments, specific information on U oxidation states and information on associated elemental distributions were obtained. Knowledge of U speciation in soils and sediments would be useful in formulating remediation strategies for U-contaminated soils.