Angularity

Angularity is a geometric property of particulate materials that describes the sharpness of a particle’s edges and corners. It is one aspect of particle shape used in conjunction with other descriptors such as roundness (the smoothness of a particle’s silhouette) and sphericity (how close a particle is to a perfect sphere). High angularity indicates pronounced edges and corners, while low angularity corresponds to smoother, more rounded grains.

In geotechnical engineering and materials science, angularity influences how particles pack and how they interact at contact points. Particles with greater angularity tend to interlock, increasing interparticle friction and shear strength, but often reducing packing density and flowability. The degree of angularity therefore affects properties such as shear strength, dilatancy, permeability, and compaction behavior of granular assemblies like sands and crushed aggregates.

Measuring angularity typically involves image-based analysis or three-dimensional scanning. Common approaches include examining particle outlines in two dimensions, applying shape indices, or approximating the grain with polygons. Results are usually reported as an angularity index or as a distribution of angularity values across a sample. Measurements are sensitive to imaging resolution, the plane of measurement, and particle size relative to the measurement system.

Angularity evolves with processing and weathering. Crushing or grinding increases angularity by creating sharp edges, while abrasion, transport, and weathering gradually reduce angularity. Consequently, samples from crushed quarry products tend to be more angular than naturally eroded or river-deposited sands.

Angularity remains a subject of ongoing research as researchers seek standardized metrics and clearer links to mechanical behavior across mineralogical systems.