¹B. Fritzke, ¹J. Götze, ²J.-M. Lange
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12852]
¹Institut for Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, Freiberg 09599, Germany
²Senckenberg Naturhistorische Sammlungen Dresden, Section Petrography, K€onigsbr€ucker Landstraße 159, Dresden 01109,Germany
Published by Arrangement with John Wiley & Sons

A systematic study of a large set of moldavites and the application of cathodoluminescence (CL)-spectroscopy with a detailed discussion of spectral features is presented. Optical CL microscopy and spectroscopy (OM-CL) were performed on 57 moldavite samples from different substrewn-fields in Germany and the Czech Republic. The extracted CL data were supported by SEM-EDX analysis. In general, two different kinds of CL colors can be distinguished: different shades of green in the matrix of the tektite glasses and a variation of blue color for lechatelierite inclusions (a pure silica-glass phase). Spectral analysis of these colors shows three CL emission bands for green and five bands for blue c. Most CL activators are structural defects of the local glass network, influenced by the crystal field. The visible green CL emission is caused by defects related to strong local disorder as well as Al-O⁻-Al defects. The blue CL emission is activated by different types of lattice defects such as nonbridging oxygen-hole center (NBOHC), self-trapped excitons (STE), and oxygen deficiency centers (ODC). Intensity variations of the CL emissions were observed for samples from the different localities, but there is no direct correlation between substrewn-fields and CL characteristics. Nevertheless, CL microscopy is a powerful tool for the high-contrast visualization of internal textures such as streaks and lechatelierite in the tektite matrix due to the luminescence properties of the defect structures in the glassy network.

Matthew J. Genge
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12830]
Impact and Astromaterials Research Centre (IARC), Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, UK
Department of Earth Science, The Natural History Museum, Cromwell Road, London, UK
Published by Arrangement with John Wiley & Sons

Basaltic micrometeorites (MMs) derived from HED-like parent bodies have been found among particles collected from the Antarctic and from Arctic glaciers and are to date the only achondritic particles reported among cosmic dust. The majority of Antarctic basaltic particles are completely melted cosmic spherules with only one unmelted particle recognized from the region. This paper investigates the entry heating of basaltic MMs in order to predict the relative abundances of unmelted to melted basaltic particles and to evaluate how mineralogical differences in precursor materials influence the final products of atmospheric entry collected on the Earth’s surface. Thermodynamic modeling is used to simulate the melting behavior of particles with compositions corresponding to eucrites, diogenites, and ordinary chondrites in order to evaluate degree of partial melting and to make a comparison between the behavior of chondritic particles that dominate the terrestrial dust flux and basaltic micrometeroids. The results of 120,000 simulations were compiled to predict relative abundances and indicate that the phase relations of precursor materials are crucial in determining the relative abundances of particle types. Diogenite and ordinary chondrite materials exhibit similar behavior, although diogenite precursors are more likely to form cosmic spherules under similar entry parameters. Eucrite particles, however, are much more likely to melt due to their lower liquidus temperatures and small temperature interval of partial melting. Eucrite MMs, therefore, usually form completely molten cosmic spherules except at particle diameters −1) and is more compatible with higher velocities which may suggest a near-Earth asteroid source dominates the current dust production of basaltic MMs.