A Review of Roundness, a Fundamental Shape Parameter of Detrital Particles: History of Analysis and Analytic Prospects

Abstract

Studies on the external geometry of detrital particles are subject to controversy. This paper reviews the history of detrital grain shape analysis, particularly “roundness”, since the first half of the 20th century and within various fields, e.g., physical geography, civil engineering, and mathematics. The authors suggest a flow chart supporting stable evaluation of grain roundness with the Krumbein roundness chart, which is suitable for prompt semi-quantitative measurement of roundness and has been commonly used. Additionally, the authors redefine surface texture, a smaller-scale shape feature, because the boundary between roundness and surface texture is ambiguous in current studies with high-resolution image analysis. The methodological transition from analogue to digital measurement, i.e., image analysis, is in progress, and two- or three-dimensional quantitative image analysis is the preferred measurement approach. It is necessary to discuss further appropriate evaluation of grain shape corresponding to image analysis.