Density, Porosity and Internal Structure of Unmelted Micrometeorites
Abstract
Physical properties and internal structure of 100-300 µm-sized melted and unmelted micrometeorites from Novaya Zemlya glacier, Russia, were investigated using x-ray microtomography (XMT) at the Department of Physics, University of Helsinki. Due to its high-voltage (20-180 kV) nanofocus x-ray tube and variable imaging geometry, the XMT equipment allows scans 10 cm to 50 µm sized samples with sub-micron resolution. XMT results indicate predominantly silicate composition of our micrometeorites. The internal structure of the unmelted micrometeorites varies from vesicular, highly porous, to compact with abundant sulphides or magnetite. Melted micrometeorites are affected by atmospheric entry and their structure varies from glassy to barred olivine with sulphides metamorphosed into metal or iron oxides. Porosity of the unmelted micrometeorites varies from 1% up to over 33 % while the grain density is in range of 2.5-3.2 g/cm3. The melted micrometeorites are compact with porosity mostly below 3% and increased grain density in range of 3.4-3.5 g/cm3. One melted micrometeorite contains large metal inclusion. This is also reflected in its higher grain density of 5.7 g/cm3 similar to stony-iron meteorites. Magnetic studies of the melted micrometeorites reveal further 4 wt% fraction of submicron-sized iron oxides which are too finely grained to be detected in the XMT scans. Generally melted micrometeorites have lower porosities and higher grain densities compared to unmelted ones and compositionally similar, carbonaceous chondrites. Porosity decrease is most likely a result of meteoroid melting and recrystallization during atmospheric entry. An increase in grain density is most likely due to the loss of volatiles or sulfur evaporation from iron bearing sulphides as troilite or pyrrhotite.XMT proves to be a capable 3D non-destructive investigation tool suitable for extraterrestrial material studies and for quantitative evaluation of its physical properties and represents a significant improvement over the SEM based methods used in earlier studies.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #44
- Pub Date:
- October 2012
- Bibcode:
- 2012DPS....4421201K