The Flickr Prismaticstructure Image Generatr

Prismatic soil structure. (Photo courtesy of Earl Blakley & John Kelley)

Soil structure refers to units composed of primary particles. Cohesion within these units is greater than the adhesion among units. As a consequence, the soil mass under stress tends to rupture along predetermined planes or zones. These planes or zones form the boundary of the structural units. Compositional differences of the fabric matrix appear to exert weak or no control over where the bounding surfaces occur. If compositional differences control the bounding surfaces of the body, then the term “concentration” is used. The term “structural unit” is used for any repetitive soil body that is commonly bounded by planes or zones of weakness that are not an apparent consequence of compositional differences. A structural unit that is the consequence of soil development is called a ped.

With prismatic soil structure, the individual  units  are  bounded  by  flat  to rounded  vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct  and  normally  flat.

Soil Survey Manual, Ag. Handbook 18, 2017, (p. 158).

An argillic horizon that begins at about 5 cm in a Haplustalf from Texas. This argillic horizon has strong prismatic structure.

In prismatic structure, the  individual  units  are  bounded  by  flat  to  rounded  vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct  and  normally  flat. 

Soil Taxonomy, 2nd Edition, 1999, (p.58).

In prismatic structure, the individual units are bounded by flat to rounded vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct or flat. Prismatic structures are characteristic of the B horizons or subsoils. The vertical cracks result from freezing and thawing and wetting and drying as well as the downward movement of water and roots.

There are five major classes of macrostructure seen in soils: platy, prismatic, columnar, granular, and blocky. There are also structureless conditions. Some soils have simple structure, each unit being an entity without component smaller units. Others have compound structure, in which large units are composed of smaller units separated by persistent planes of weakness. (Field Book for Describing and Sampling Soils; pp. 2-53.)

For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
or Chapter 3 of the Soil Survey manual:
www.nrcs.usda.gov/sites/default/files/2022-09/The-Soil-Su...

For additional information on "How to Use the Field Book for Describing and Sampling Soils" (video reference), visit:
www.youtube.com/watch?v=e_hQaXV7MpM

In prismatic structure, the individual units are bounded by flat to rounded vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct and normally flat. Prismatic structures are characteristic of the B horizons or subsoils. The vertical cracks result from freezing and thawing and wetting and drying as well as the downward movement of water and roots. These prisms are from the Btx horizon of the Hosmer soil series:

"Btx1--76 to 114 cm (30 to 45 inches); yellowish brown (10YR 5/6) silt loam; strong very coarse prismatic structure; very firm; few fine flattened roots between peds; many distinct brown (7.5YR 4/4) clay films on faces of peds; many distinct light brownish gray (10YR 6/2) clay depletions in pores and on faces of peds; brittle; very strongly acid; gradual wavy boundary."

soilseries.sc.egov.usda.gov/OSD_Docs/H/HOSMER.html

There are five major classes of macrostructure seen in soils: platy, prismatic, columnar, granular, and blocky. There are also structureless conditions. Some soils have simple structure, each unit being an entity without component smaller units. Others have compound structure, in which large units are composed of smaller units separated by persistent planes of weakness.

For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
or Chapter 3 of the Soil Survey manual:
www.nrcs.usda.gov/sites/default/files/2022-09/The-Soil-Su...

For additional information on "How to Use the Field Book for Describing and Sampling Soils" (video reference), visit:
www.youtube.com/watch?v=e_hQaXV7MpM

For more information about Hosmer soils, visit:
soilseries.sc.egov.usda.gov/OSD_Docs/H/HOSMER.html