Porosity and density of ordinary chondrites: Clues to the formation of friable and porous ordinary chondrites

Densities and porosities of meteorites are physical properties that can be used to infer characteristics of asteroid interiors. We report density and porosity measurements of 42 pieces of 30 ordinary chondrites and provide a quantification of the errors of the gas pycnometer method used in this study. Base on our measurements, we find that no significant correlation exists between porosity and petrologic grade, chemical group, sample mass, bulk and grain density, or shock level. To investigate variations in porosity and density between pieces of a meteorite, we examined stones from two showers, Holbrook and Pultusk. Examination of nine samples of Holbrook suggests relative homogeneity in porosity and density between pieces of this shower. Measurements of three samples of Pultusk show homogeneity in bulk density, in contrast to Wilkison and Robinson (2000), a study that reported significant variations in bulk density between 11 samples of Pultusk. Finally, examination of two friable ordinary chondrites, Bjurböle and Allegan, reveal variability in friability and purosity among pieces of the same fall. We suggest that friable ordinary chondrites may have formed in a regolith or fault zone of an asteroid.