ABSTRACT

Distinction is made between form indices which describe the geometry of a particle in terms of its dimensions and functional indices which describe its behavior as a ratio of the value of a behavioral characteristic to the value of the same characteristic for a reference body. No single index of either kind can describe a particle uniquely. Thirteen dimensional parameters are suggested as necessary to describe a particle, and a range of form indices is derived from these, such that each index partially closes the gap between the previous approximation and the true form of the particle. The indices are not completely independent of each other, and roundness is shown to be geometrically dependent on sphericity.

The form of a particle determines its mode of transport, its abrasion, point of deposition, and its effect on the resulting sedimentary rock. Each behavioral characteristic depends in a different way on each form index which defines the particle, and a general correlation can only be obtained by successive experiments in which performance is tested against mass, volume, axial ratio, asymmetry, and indices defining surface irregularities. This analysis has been carried furthest in the case of settling velocity.

It is proposed that the system outlined here provides a basis for correlation of other behavioral characteristics with form.