Internal structure of type I deep-sea spherules by X-ray computed microtomography

The internal structures of type I spherules (melted micrometeorites rich in iron) have been investigated using synchrotron-based computed microtomography. Variations from sphericity are small-the average ratio of the largest to the smallest semimajor axis is 1.07 ± 0.06. The X-ray tomographs reveal interior cavities, four spherules with metal cores with diameters ranging from 57 to 143 μm and, in two spherules, high attenuation features thought to be nuggets rich in platinum-group elements. Bulk densities range from 4.2 to 5.9 g/cm³ and average grain densities from 4.5 to 6.5 (g/cm³) with uncertainties of 10-15%. The average grain densities are those expected for materials containing mostly oxides of iron and nickel. The tomographic density measurements indicate an average void space of 5_-5⁺⁸%. The void spaces may be contraction features or the skeletons of bubbles that formed in the molten precursors during atmospheric passage.