Volume and surface-area measurements using tomography, with an example from the Brenham pallasite meteorite

Authors:
Jacob Spinsby;Heiner Friedrich;Peter R. Buseck
Affiliations:
School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA;Inorganic Chemistry and Catalysis, Utrecht University, The Netherlands;School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA and Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, USA
Venue:
Computers & Geosciences
Year:
2008

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Abstract

Increased computer speed has helped to proliferate tomography throughout the geosciences. Although best known from the medical CATscan, tomography is also a powerful tool for geological problems. Whereas qualitative tomography is widely used, quantitative data from tomograms are not so commonly available. Presented here are two programs, Electron Tomography Segmentation, surface Area, and Volume (ETSAV) and Electron Tomography CUTter (ETCut), that were written to obtain quantitative volume and surface-area data from tomograms. Based on a specified threshold value, ETSAV distinguishes objects within a tomogram and then returns volume and surface-area data for each object. If object separation is unsatisfactory using a single threshold, ETCut is called to digitally separate objects that appear connected in the tomogram, allowing ETSAV to perform its functions. By knowing the nature of the object of interest, error can be corrected to, on average, less than 5% for a single object; combined volumes of many particles of different sizes may result in lesser errors. A section of the Brenham pallasite meteorite was examined using the programs. Olivine comprises 67.2% of the volume (50.4%wt%), followed by FeNi metal at 23.1% (39.3%wt%), troilite at 4.4% (4.8%wt%), and schreibersite at 3.4% (5.5%wt%). In all, 56.1% and 44.7% of the troilite and schreibersite surface areas, respectively, border olivine, suggesting that they wet olivine. Since the programs can be applied to any tomogram, from any field, there are many potential applications.