There has been a historical need for sedimentologists to refine the characterization of both particle size and shape. Automated sizecharacterization instruments have improved on “classical” techniques, such as the sieve and pipette method, in terms of speed and precision. However, many of these instruments provide a size frequency distribution of particle diameters from a population of sediment grains by proxy (i.e., by converting a particle's cross-sectional area, surface area, volume, settling velocity, or some other form of particle behaviour, to particle diameter). Some techniques, such as the settling tube, may involve user-built instruments not yet calibrated in the traditional analytical sense. To this end, the International Union of Geological Sciences – Committee on Sedimentology (IUGS–COS) sponsored this study to compare the results from automated instruments that measure the frequency distribution of grain diameters in geological samples. This chapter reviews some of the previous attempts at interlaboratory or interinstrument calibration, discusses the philosophy and preparation of geological standards (silts and sands), and presents new results with recommendations for future experiments.
Grain size and calibration standards
The size of a particle is not uniquely defined, except for the most simple of geometric objects – the sphere. For natural and irregularly shaped particles, size depends on the method of measurement. Allen (1968) provides a number of differing definitions of particle size, including surface diameter, volume diameter, drag diameter, projected area diameter, free-falling diameter, Stokes's diameter, sieve diameter, and specific surface diameter.