Discovery of coesite and stishovite in HED meteorite
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Coesite and stishovite in a shocked lunar meteorite, Asuka-881757, and impact events in lunar surface.
Microcrystals of coesite and stishovite were discovered as inclusions in amorphous silica grains in shocked melt pockets of a lunar meteorite Asuka-881757 by micro-Raman spectrometry, scanning electron microscopy, electron back-scatter diffraction, and transmission electron microscopy. These high-pressure polymorphs of SiO(2) in amorphous silica indicate that the meteorite experienced an equili...
متن کاملThermodynamics of polymorphic transformations in silica. Thermal properties from 5 to 1070°K and pressure-temperature stability fields for coesite and stishovite *
Cryogenic heat-capacity measurements on coesite and stishovite provide thermodynamic properties from 5 to 350°K. The heat capacities (C,), entropies (SO), and Gibbs energy functions [-(Go H”,)/T] are 10.85, 9.65, 4.124, and 10.27, 6.64, 2.362 at 298015°K for coesite and stishovite, respectively, in Cal/( mole “K). Enthalpies of transition for phase changes were determined by solution calorimetr...
متن کاملShock Processes in Porous Quartzite: Transmission Electron Microscope Observations and Theory
A high-resolution study of shocked Coconino Sandstone from Meteor Crater, Arizona, was undertaken using transmission electron microscopy to investigate the textural relations of high-pressure phases produced by meteorite impact. In weakly shocked rocks (estimated average pressure, P < 100 kb), quartz in the interiors of grains retains its initial microstructure, but near original grain boundari...
متن کاملShock Metamorphism of the Coconino Sandstone at Meteor Crater, Arizona
A study of the shocked Coconino sandstone from Meteor Crater, Arizona, was undertaken to examine the role of porosity in the compression of rocks and in the formation of highpressure phases. A suite of shocked Coconino. specimens collected at the crater is divided into five classes, arranged in .order of decreasing quartz content. The amounts of coesite, stishovite (measured by quantitative X-r...
متن کاملHigh-pressure minerals in eucrite suggest a small source crater on Vesta
High-pressure minerals in meteorites are important records of shock events that have affected the surfaces of planets and asteroids. A widespread distribution of impact craters has been observed on the Vestan surface. However, very few high-pressure minerals have been discovered in Howardite-Eucrite-Diogenite (HED) meteorites. Here we present the first evidence of tissintite, vacancy-rich clino...
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تاریخ انتشار 2012