Modelling and analyzing dredging and disposal activities using Telemac, Sisyphe and DredgeSim

Water Qualit

Structural and compositional variations of basic Cu(II) chlorides in the herbertsmithite and gillardite structure field.

© 2017 The Mineralogical Society. This document is the author’s final accepted version of the journal article. You are advised to consult the published version if you wish to cite from it

The modulated low-temperature structure of malayaite, CaSnOSiO4

The crystal structure of the mineral malayaite has been studied by single-crystal X-ray diffraction at a temperature of 20 K and by calculation of its phonon dispersion using density functional perturbation theory. The X-ray diffraction data show first-order satellite diffraction maxima at positions q = 0.2606 (8)b*, that are absent at room temperature. The computed phonon dispersion indicates unstable modes associated with dynamic displacements of the Ca atoms. The largest-frequency modulus of these phonon instabilities is located close to a wavevector of q = 0.3b*. These results indicate that the malayaite crystal structure is incommensurately modulated by static displacement of the Ca atoms at low temperatures, caused by the softening of an optic phonon with Bg symmetry

The atacamite family of minerals : a testbed for quantum spin liquids

Polymorphism of Cu 2 (OH) 3 Cl coupled with partial substitution of Jahn–Teller active Cu 2+ by other divalent metal cations gives rise to the complex mineralogy of the atacamite family of secondary basic copper chlorides. Herbertsmithite, Cu 3 Zn(OH) 6 Cl 2 , in which Zn substitutes for one quarter of the Cu atoms, provides a lattice of corner-sharing triangles of paramagnetic Cu 2+ (spin ½) cations, rendering the mineral a perfect realization of a kagome antiferromagnet. Geometric frustration of conventional antiferromagnetism is expected to give rise to exotic ground states, with dynamic magnetic structures that might turn out to be physical realizations of quantum spin liquids. In this paper, a synopsis of the key topological, compositional and behavioural features of minerals in the atacamite family is given, with emphasis on the kagome character of the resulting lattice of Cu 2+ cations

Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks

Tourmalines, XY3Z6T6O18(BO3)3V3W, are excellent petrogenetic indicators as they capture the signature of the host-rock bulk composition. Raman spectra of tourmalines can be used as fingerprints for species identification and crystal-chemical analysis. While Li-bearing species are directly distinguishable by the shape of the OH-stretching vibrations, the discrimination of Mg- and Fe-dominant species can be hindered by the coexistence of at least two types of octahedrally coordinated Rn+ cations. Thirty Li-free tourmaline samples comprising 14 different species were studied by Raman spectroscopy and electron microprobe. All nine Fe3+-bearing samples were also analyzed by single-crystal X‑ray diffraction and Mössbauer spectroscopy. The Raman scattering analysis shows that Mg-dominant species can be immediately distinguished from Fe-dominant species by the shape of the vibrational modes at ~200–240 cm–1 arising from the YO6 vibrations. Trivalent Fe can be observed and quantified by shifts of the framework vibrations toward lower wavenumbers. The position of the main ZO6 vibrational mode (275–375 cm–1) can be used to determine the ZFe3+ content, while the YFe3+ content can be inferred from the position of the peak at ~315 cm–1. Fits to the data points indicate that the homovalent substitution of Fe3+ for Al3+ leads to a considerably larger downward shift of the ZO6 vibrational mode than the heterovalent substitution Mg2+ for Al3+. The intensity ratio of the two major YO6 vibrational modes (200–240 cm–1) of the fully characterized Fe3+-bearing samples reflects the amount of Y-site Mg and thus can be used to deduce the site-occupancy disorder of Mg over the Y and Z site for tourmaline species with Mg ≤2 apfu. By combining the information from framework and OH-stretching vibrations, Raman spectroscopy alone can be used as a micrometer-scale sensitive non-destructive method for the analysis of tourmaline crystal chemistry including trivalent Fe, which is the major tracer for oxygen fugacity and central for intersite geothermometry