The porosities of ordinary chondrites: Models and interpretation

Abstract

Abstract-Densities and porosities for 285 ordinary chondrites have been assembled and analyzed. Measured chondrite porosities are bimodal; finds have an average porosity of <3%, whereas fall porosities average 7% but range from zero to >30%. We conclude that mild degrees of weathering fill pore spaces, lowering grain densities and porosities without significantly changing the bulk size or mass of the sample. By assuming an original pristine grain density (as a function of the meteorite's mineralogy-determined by its class), we can derive model pristine porosities. These model porosities cluster around an average value of 10% for all classes of ordinary chondrites.Ordinary chondrites do not show any correlation of porosity (model or measured) with petrographic grade or sample size (over a range from 0.2 g to 2 kg). However, we do see a correlation between shock state and porosity. Shock-blackened meteorites are less porous than other meteorites. Furthermore, less severely shocked meteorites show a much broader range of porosities, with the maximum porosity seen among meteorites of a given shock class falling linearly as a hnction of that shock class. This is consistent with the idea that shock compresses and closes pore space.Analysis of meteorite porosity provides a lower bound to the fine-scale porosity of asteroids. Our densities, even with 10% primordial porosity, are significantly higher than inferred densities of possible asteroid parent bodies. These asteroids are probably loose piles of rubble.

The density and porosity of meteorites from the Vatican collection

“…This suggests that the process of terrestrial weathering tills-in the pore space of the meteorite with less dense weathering products, like iron oxides and clays, without significantly changing the bulk density. This has implications for the nature of the terrestrial weathering process, which we have discussed elsewhere (Consolmagno et al, 1997a(Consolmagno et al, , 1998 Editorial handling: R. P. Binzel…”

Weathering of meteorites from Oman: Correlation of chemical and mineralogical weathering proxies with14C terrestrial ages and the influence of soil chemistry

“…porosity, demonstrated by Lee and Bland (2004). Based on a typical chondrite porosity of 10 vol% (Consolmagno et al 1988), L chondrites with low porosity and most H chondrites will experience a significant bulk volume increase.…”

Asteroid 6 Hebe: The probable parent body of the H‐type ordinary chondrites and the IIE iron meteorites

“…Water is absent on the H-chondrite parent body, and unweathered H chondrites have intrinsic porosities of -10% (-90% of samples falling in the 5-20% range of porosity; Corrigan et Consolmagno et al, 1998). If-as now appears certain-there are substantial surface regoliths on the larger asteroids (Belton et al, 1994), the bulk porosity (i.e., intrinsic porosity plus regolith porosity) of the surface layer of Hebe must be substantial; it is almost certainly greater than the lower limit (23%) for the bulk porosity of asteroid Ida inferred from the Galileo flyby-(23-73% depending on meteorite type and Ida mass; Belton et al, 1995).…”