| Summary: | Introduction: Micrometeorites (MMs) are microscopic particles, collected at the Earth’s surface and mainly produced by collisions among solid bodies and by surface evaporation of icy bodies in the Solar System [1]. As such, they provide important information on the compositon of their parent bodies including those that are not sampled by meteorites. I-type cosmic spherules (CS) are dark, opaque, melted micrometeorites dominated by magnetite (Fe3O4) and wüstite (FeO) crystals. I-type CS frequently contain μm-sized Ni-rich Fe,Ni metal beads [2] as well as μm- and nmsized platinum-group element (PGE) nuggets [3]. The aim of this work is twofold: 1) to study the internal textural and structural components (i.e. iron oxides domains, metal beads, PGE nuggets, cavities) of the I-type CS, 2) to characterize the distribution of the metal beads and PGE nuggets and estimate their relative volume/mass. Samples: I-type CS have been collected in loose sediments sampled on the tops of the Transantarctic Mountains [4] during the 2012-13 and 2014-15 Italian Programma Nazionale di Ricerche in Antartide (PNRA) campaign. In Antarctic MMs collections the abundance of I-type spherules is typically less than 2% [5]. Our collection consists of over 3000 MMs. Among these 107 (3.2% of the total) are I-type CS. For this study we have selected 52 I-type CS, ranging from 200 to 800 μm in diameter and 2 with diameters <150 μm. They look fresh (unweathered) under the stereomicroscope-SEM and provide excellent material for our study. Methods: The external morphology of CS has been described by SEM analyses. Subsequently, non-destructive mapping of I-type CS has been carried out by X-ray microcomputed tomography (micro-CT) using a Zeiss Xradia 520 Versa 3D X-ray microscope, at the Electrochemical Innovation Lab, part of the Department of Chemical Engineering of University College London. The microscope was operated at 140 kV with a high energy filter in place (HE1) and an optical magnification of 20X. Results and Discussion: So far 3D ...
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