How do particle size and particle shape affect sample mixing?

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Viking 1 on Mars — sample preparation Viking 1's sample scoop, poised to extract material from the surface of Mars.

In analytical chemistry, the effectiveness of mixing a laboratory sample is significantly influenced by the physical characteristics of the particles, including their size, shape, and density.1

When a sample contains a broad range of particle sizes and shapes, mixing processes must actively overcome natural segregation tendencies. Specifically, particles of different morphologies behave differently during handling: fine particles tend to migrate toward the center of a pile, while rounded particles gravitate toward the edges.1

Furthermore, while reducing particle size is often necessary to achieve a representative test sample, there are practical limitations. If material is ground too finely, it can become impossible to mix adequately. Consequently, mixing is a critical operation that must be performed after each step of particle size reduction to ensure the resulting subsample remains representative of the original material.1