(Definitions are largely copied from: Brewer, R. 1976. Fabric and mineral analysis of soils. Robert E. Krieger Pub. Co., Huntington, New York.)

Most mineral soils consist essentially of mineral grains of various sizes, shapes and arrangements, which results in the occurrence of voids of different size, shape and pattern. The constituents of most mineral soils may be divided into constituents that are relatively stable in their physical and chemical properties (skeletal grains) and relatively unstable material that may be translocated, precipitated, or reorganized by soil forming processes.

Concepts of Structure and Fabric often differ among and within disciplines. The following difinitions deal with some aspect of the physical constitution fo the material being described.

Skeleton grains. Individual grains larger than colloidal size; they consist of mineral grains originally present in the parent material and resistant siliceous and orgainc bodies. Not readily translocated, concentrated or reorganized by soil forming processes.

Plasma. All the material of colloidal size, and relatively soluble material that is not bound up in skeleton grains; it consists of mineral (amorphous and crystalline) and organic material. It is that part of the soil material that is capable of being or has been translocated, reorganized, and/or concentrated by the process of soil formation. It is the mobile, active part of the soil material.

Ped. An individual natural soil aggregate consisting of a cluster of primary particles, and septarated from adjoining peds by surfaces of weakness which are recognizable as natrual voids or by the occurrence of cutans. This is an objective definition without regard to size and/or shape.

Apedal. Applied to soil materials without peds.

Soil Fabric. The physical constitution of a soil material as expressed by the spatial arrangement of the solid particles and associated voids. Soil Fabric is not only concerned with the spatial arrangement of discrete grains and associated voids, but also with compound particles and the voids between compound particles.

Soil Structure. Teh physical constitution of a soil material as expressed by the size, shape, and arrangement of the solid particles and voids, including both the primary particles to form compound particles and compound particles themselves; fabric is the element of the structure which deals with arrangement.

Soil Texture. The physical constitution of a soil material as expressed by its structure, and by the degree of crystallization (crystallinity) of the solid particles; fabric is a part of structure, which is a part of texture in this context.

Pedological Features. Recognizable units within a soil material which are distinguishable from the associated material for any reason, such as origin (deposition as an entity), differences in concentration of some fraction of the plasma, or differences in arrangement of the constituents (fabric).

Plasma Concentrations. Concentrations of any of the fractions of the plasma in various parts of the soil material. Examples of these are carbonate nodules, iron oxide nodules and clay mineral coatings.

Plasma Separations Features characterized by a significant change in the arrangement of the constituents, rather than a change in concentration of some fraction of the plasma. Rearrangements often caused by differential pressures producing shear forces (slickensides).

Fossil Formations. Preserved features resulting from biological activity, such as burrows and root channels.

Lithorelicts. Features derived from the parent rock; usually recognizable by their rock structure and fabric.

Pedorelicts. Features formed by erosion, transport and deposition of nodules of an older soil material or pedological features from it, or by preservation of some part of a previously existing soil horizon within a newly formed horizon.

Sedimentary Relicts. Features formed during depostion of a transported soil parent material, for example, clay galls.

Orthic Pedological Features. Pedological Features formed in situ in the soil material by soil forming processes (genetic).

Inherited Pedological Features. Pedological Features inherited from other materials, such as the parent material, parent rock, underlying materials or previously existing soil horizons.

S-matrix. The material (plasma and/or skeleton grains and associated voids) withing the simplest (primary) peds, or composing apedal soil materials that does not occur as pedological features other than plasma septarations; it may be absent in some soil materials, for example, those that consist of pedological features. It is the background material within which pedological featuers occur and includes plasma separations.

Basic Structure. The structure of the s-matrix, that is, the size, shape, and arrangement of simple grains (plasma and skeleton grains) and voids in primary peds or apedal soil material, excluding pedological features other than plasma separations.

Plasmic Structure. The structure of the plasma of the s- matrix; that is, the size, shape and arrangement of the plasma grains and associated packing voids. It is the orgainization of the constituents of the plasma that have not been concentrated or crystallized to form pedological features and the associated small voids which result from packing of plasma grains.

Primary Structure. The structure within an apedal soil material or within primary peds in the pedal soil material; it is an intergration of the size, shape, and arrangement of all pedological features enclosed in the s-matrix and the basic structure or structure of the s-matrix.

This page (http://www.ces.ncsu.edu/plymouth/programs/fab.html) created by
Vera MacConnell, Research Technician, I on December 12, 1997.
Last Updated on December 12, 1997.