Density, magnetic susceptibility, and the characterization of ordinary chondrite falls and showers

Abstract

Bulk and grain densities of 132 ordinary chondrites from the Vatican Observatory collection were measured and compared with their magnetic susceptibility (for the most part using previously measured values; ten new susceptibility measures were taken for this study). Grain density and magnetic susceptibility combined provide a reliable method of classifying un weathered ordinary chondrites. Unlike traditional chemical tests, this method is fast, nondestructive, and characterizes the whole rock, making it especially appropriate for surveying large collections. The system is less viable for finds; extensive weathering of metallic iron in an H chondrite can cause it to plot among L chondrites, while heavily weathered L chondrites plot among the LL group. This system has revealed outlier stones that may be misclassified meteorites or mislabeled samples; in every case where the magnetic susceptibility of a meteorite does not fit its putative classification, the grain density is also found to be in disagreement in a manner consistent with either severe weathering or misidentification. An analysis of stones from five showers shows that, excluding outliers, these samples tend to cluster tightly within their appropriate groups in a plot of grain versus magnetic susceptibility.