Three-dimensional imaging of ordinary chondrite microporosity at 2.6 μm resolution

We show that high resolution (2.6 μm/voxel) synchrotron X-ray microtomography (μCT) scans are able to observe the majority of microporosity in ordinary chondrites. This porosity is present in the form of microcracks and voids among and between mineral grains. We examined, in total, seven small (6–12 mm3) chips of the ordinary chondrites Baszkówka (L5, S1), ALH A77258 (H5, S2), Moorleah (L6, S3), and Kyushu (L6, S5). These four samples were chosen because of their variable impact histories. Using μCT and various digital isolation and visualization techniques, we found that the structure of microporosity varies with the degree of compaction and shock loading experienced by the materials. The microporosity in the compacted and more strongly shock samples Moorleah and Kyushu is visible as sheet-like fractures within brittle silicates as well as in discontinuous, distributed voids sometimes associated with chondrule rims and grain boundaries. In samples that have experienced less shock and only mild compaction, we found few, if any, microcracks in the silicate grains of the materials. Microporosity in the Baszkówka and ALH A77258 samples is largely represented by intergranular voids, with occasional intragranular voids being present. Regardless of degree of shock loading, ductile Fe–Ni or FeS grains give no evidence of shock-related internal fractures contributing to porosity.