Abstract Non-stoichiometric minerals have a chemical composition that cannot be expressed by a nominal cation to anion ratio. The excess or deficiency of ions in these minerals is commonly due to extrinsic vacancies that result from the substitution of cations in different valence states. The vacancies are invisible as long as they are isolated but become observable in the transmission electron microscope once they cluster or order into specific crystallographic directions or planes. The ordering of vacancies results in the formation of defect clusters or superstructures in minerals that greatly alter, in particular, magnetic and transport properties (diffusivity, conductivities) of minerals. This chapter surveys structural modifications in the non-stoichiometric minerals pyrrhotites (Fe 1–x S), wüstite (Fe 1–x O), rutile (TiO 2 ), and perovskites (ABO 3 –x ). The examples provide an instructive overview of how both cation deficiency and cation excess are accommodated by common crystal structures relevant to geoscience.

The International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville B core hole, drilled into the 35.5-Ma-old Chesapeake Bay impact crater, Virginia, has recovered postimpact sediments, crater-fill breccias, megablocks of the crystalline basement, and suevites with fresh glass shards. Bulk rock analyses of 2 glass shards, 21 crystalline target rocks, and microchemical analyses of 7 glass shards and 3 bediasites (tektites of the North American strewn field) were performed in order to contribute to the understanding of formation processes and to better constrain the precursor materials of these glasses as well as of the bediasites. Statistical treatment (hierarchical cluster analyses) yielded an assignment of the data for the crystalline basement samples into four groups; two of those (various schists, meta-graywackes, and gneisses) display characteristics similar to the impact glasses in the suevites and the bediasites. However, the suevitic glasses show a broad range in composition at the micrometer scale. These data show the frequent presence of schlieren, and in particular, enhanced TiO 2 contents that require admixture of an “amphibolitic component” to the melt. Evidence for such a process is provided by the occurrence of relict, in-part thermally corroded grains of rutile and ilmenite, and by formation of Ti-rich tiny mineral aggregates in the glass. The three studied bediasites show only minor inter- and intrasample heterogeneity, and their chemical composition agrees well with previously published data. The new data for the bediasites are compatible with heating of the “tektite melt” to extreme temperatures, followed by quenching.

The Cretaceous-Tertiary boundary is characterized by mass extinctions triggered by a large body impact into predominantly limestone-, dolomite-, and anhydrite-bearing sediments of the Yucatan peninsula, Mexico. Decomposition of these volatile-rich minerals and associated deterioration of the atmosphere and hydrosphere rank among the most prominent kill mechanisms during this global catastrophe. As a consequence, we conducted optical and scanning electron microscopy and X-ray diffraction studies of anhydrite (CaSO 4 ) that was experimentally shock-loaded to pressures from 4 to 64 GPa to determine the shock damage and potential loss of volatiles as a function of shock stress. We did not find any decomposition products in any of the recovered samples. It appears that anhydrite is stable over a wide pressure range (up to 64 GPa). Peak widths of the X-ray diffraction powder patterns increase with peak shock pressure up to ∼50 GPa, yet the peaks become narrower again above this pressure, implying some recrystallization.

Abstract About half a century ago the first experimental shock techniques and the basic laws governing the propagation of shock waves have been developed. During these early post-war years Russian and American pioneers were already able to experimentally compress solids to half of their specific volumes (see Trunin, 1998 , or Zel’dovich & Raizer, 2002 , for a review), i.e. pressures prevailing in the Earth’ s core were reproducible in laboratory shock experiments long before static compression techniques such as the diamond anvil cell approached this limit. The strength of shock experiments particularly lies in the fact that a combination of high pressures and high temperatures can be achieved, while the attainment of high temperatures is still problematic in diamond anvil cell experiments. In Earth and planetary sciences there are numerous basic interests in employing shock techniques. On one hand, shock experiments are devoted to the measurement of the shock wave equation of state of minerals and rocks at extreme conditions ( Wackerle, 1962 ; Grady, 1977 ; Marsh, 1980 ; Ahrens, 1987, 1993 ; Boslough & Ahrens, 1984 ; Ahrens & Johnson, 1995a, 1995b ). Virtually, the entire range of pressures and temperatures prevailing in the Earth’ s and planetary interiors can be reproduced in the laboratory. In this context, important applications of shock wave data are the correlation of the pressure–density function with the inner structure of planets and the assessment of the melting temperatures at which planetary magma oceans can be produced.

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