Long-term relaxation of orientational disorder and structural modifications in molecular nitrogen at high pressure.

Up to 17 GPa, the crystalline phases of N2 are characterized by pronounced orientational disorder, whereas the higher-pressure phases of molecular N2 are ordered. This raises the question about long-term relaxation of orientational disorder within the low- to intermediate-pressure regime. Here, this question is addressed by comparing synthetic with natural, chemically pure, solid N2 that resides as inclusions in diamonds at 300 K for about 108 years at pressures up to 11 GPa.

Crystal Structure Complexity and Approximate Limits of Possible Crystal Structures Based on Symmetry-Normalized Volumes.

Rules that control the arrangement of chemical species within crystalline arrays of different symmetry and structural complexity are of fundamental importance in geoscience, material science, physics, and chemistry. Here, the volume of crystal phases is normalized by their ionic volume and an algebraic index that is based on their space-group and crystal site symmetries. In correlation with the number of chemical formula units Z, the normalized volumes exhibit upper and lower limits of possible structures.

Response to Comment on "Discovery of davemaoite, CaSiO-perovskite, as a mineral from the lower mantle".

Walter . issue a number of critical comments on our report about the discovery of davemaoite to the end that they believe to show that our results do not provide compelling evidence for the presence of davemaoite in the type specimen and that the hosting diamond had formed in the lithosphere. Their claim is based on a misinterpretation of the diffraction data contained in the paper, an insufficient analysis of the compositional data that disregards the three-dimensional distribution of inclusions, and the arbitrary assumption that Earth's mantle shows no lateral variations in temperature, inconsistent with state-of-the-art assessments of mantle temperature variations and with their own published results.

Discovery of davemaoite, CaSiO-perovskite, as a mineral from the lower mantle.

Calcium silicate perovskite, CaSiO, is arguably the most geochemically important phase in the lower mantle, because it concentrates elements that are incompatible in the upper mantle, including the heat-generating elements thorium and uranium, which have half-lives longer than the geologic history of Earth. We report CaSiO-perovskite as an approved mineral (IMA2020-012a) with the name davemaoite. The natural specimen of davemaoite proves the existence of compositional heterogeneity within the lower mantle.

Coupled deep-mantle carbon-water cycle: Evidence from lower-mantle diamonds.

Diamonds form in a variety of environments between subducted crust, lithospheric and deep mantle. Recently, deep source diamonds with inclusions of the high-pressure HO-phase ice-VII were discovered. By correlating the pressures of ice-VII inclusions with those of other high-pressure inclusions, we assess quantitatively the pressures and temperatures of their entrapment.