the physical combination or arrangement of primary soil particles into secondary aggregates or peds —note 1. the principal forms of soil structure are platy (laminated), prismatic (vertical axis of aggregates longer than horizontal), columnar (prisms with rounded tops), blocky (angular or subangular), and granular —note 2. structureless soils are either single-grained (as in a dune sand) or massive —see clod This definition last updated 10/07/2008