Microstructure: there are a large number of possible microstructures. Some have been given names and definitions. Others have not been assigned names. Thin sections of heterogeneous soil material may contain more than one type of microstructure. The following lists the most commonly occurring microstructures, but does not cover all possibilities. there is sometimes a close relationship between microstructure and related distribution patterns. However, since the two emphasis differenct aspects there is justification for separately describing them.

Single grain structure: almost entirely sand- sized grains; little or no fine material in intergranular spaces; grains either loose or only partly touching.
Bridged grain structure: Almost entirely sand-sized grains with most grains coated by fine material.
Pellicular grain structure: Almost entirely sand-sized grains between which are micr-aggregates of fine material.
Intergrain micro-aggregate structure: Almost entirely sand-sized grains between which are micro-aggregates of fine material.
Intergrain vesicular pore structure: Almost entirely sand-sized grains; there are numerous vesicles in addition to the normal simple packing voids.
Intergrain channel structure: Almost entirely sand-sized grains between which, in addition to the normal simple packing voids, is a system of channels.
Compact grain structure: almost entirely sand-sized grains most of which link together so that the pore pattern is dominantly closed intergranular.
Vughy structure: No separated aggregates. Mass broken up by scattered but not interconnected vughs and associated channels and chambers.
Spongy structure: Few, if any, fully separated aggregates. Much pore space; voids often strongly interconnected.
Channel structure: No separated aggregates; dominant voids are channels.
Chamber structure: No separated aggregates; dominate voids are chambers.
Vesicular structure: No separated aggregates; dominate voids are vesicles.
Crumb structure: Granules are separated by compound packing voids and do not accommodate each other. Contains few or no voids or recognizable smaller units.
Subangular blocky structure: Aggregates are separated by short planar voids on all or most sides. Vughs and small channels often occur within the aggregates which may contain groups of partially welded crumbs. Aggregate faces largely accommodate each other.
Angular blocky structure: Aggregates have angular edges, few voids and are separated by an intricate system of planar voids. Faces of aggregates normally accommodate each other.
Platy structure: Stacks of aggregates generally horizontally elongated and separated by planar voids. Interior voids variable.
Prismatic structure: The soil material is divided into prisms separated by verticlly aligned planar voids. Faces of the prisms accommodate each other. Seen only in mammoth-sixe thin sections.
Fissure structure: Few, if any, fully separated aggregates; many interconnections of planar voids.
Crack structure: No fully separated aggregates. Material dense except for a few planes (and occasional channels).
Massive structure: No separated peds, and few if any voids visible.
Complex structure: consists of mixture of two or more structure types. Combined terms can be used to name the structure of the whole thin section.

This page (http://www.ces.ncsu.edu/plymouth/programs/types.html) created by
Vera MacConnell, Research Technician, I on February 4, 1998.
Last Updated on February 4, 1998.