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Quantifying Grain Shape in Three Dimensions: Advancing Morphological Techniques for Planetary Samples

Session: Geomorphology and Surface Processes Across the Solar System

Presenting Author:

Kashauna G. Mason

Authors:

Mason, Kashauna G.¹, Ewing, Ryan Cotter², Reece, Julia³, Bullard, Jeffrey⁴, Eckley, Scott Allan⁵

(1) Texas A&M University, College Station, TX, USA, (2) Astromaterials & Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA, (3) Texas A&M University, College Station, TX, USA, (4) Texas A&M University, College Station, Texas, USA, (5) Amentum, NASA Johnson Space Center, Houston, TX, USA,

Abstract:

Understanding sediment particle morphology is essential for reconstructing depositional environments and surface processes, especially in planetary science, where direct sampling is limited. Traditional particle size and shape analysis methods such as sieving, laser diffraction, and 2D image analyses are either destructive, resolution-limited, or inherently biased by assumptions about particle orientation and symmetry.

This study compares two state-of-the-art methods for quantifying particle size and shape: 2D Dynamic Image Analysis (DIA) and 3D micro-X-ray computed tomography (µXCT). It further explores 3D shape parameters using µXCT to refine 3D techniques for in-situ geological and planetary sample analysis. We analyzed four sediment samples, one aeolian and one fluvial, each from basaltic (Iceland) and quartzofeldspathic (Texas) sources as terrestrial analogs for Martian settings.

We found that grain size distributions between the two methods are generally similar; however, sphericity (Ψ = 0.7 - 0.9 across all samples) is consistently lower for µXCT. Relationships between grain size and shape are more apparent in DIA, though this may partly result from the binned nature of the data. Across the four samples, 3D metrics such as Krumbein’s sphericity and aspect ratios (thickness/length and width/length) show that these metrics are strongly influenced by elongation and flattening relative to the longest axis. Understanding these relationships aids in determining which shape metrics are appropriate for particular settings.

Also, µXCT enables the generation of detailed 3D reconstructions of individual sediment particles. These virtual particles allow comprehensive visual inspection of particle geometry from any angle and provide further insight into surface texture and overall shape, along with their qualitative size and shape characteristics.

Our results highlight that although both methods yield comparable grain size distributions, µXCT provides better insights into true 3D shape characteristics. Our findings demonstrate the critical value of 3D analysis in particle morphology, particularly for planetary analog research. A deeper understanding of sediment shape can directly improve interpretations of sediment transport regimes and paleoenvironments on Mars, Earth, and other planetary bodies.