OTHER DEFINITIONS:

Amorphous and microcrystalline Material- The three most common forms are allophane, ferric hydroxide and opal.

Anisotropic Surfaces- False Coatings-Surfaces of peds and pores that show a marked orientation of the fine material parallel to the surface, causing the development of anisotropism which may look like a clay coating, but on close examination it contains a similar or only slightly diminished frequency of coarse material.

Clay Plugs- Pores completely filled with clay. Sometimes the form of the clay suggests that deposition has been the method of formation starting as a clay coating but in other cases the mechanism is not known.

Coatings- Deposits of material on the surface of peds, pores, rock fragments and detrital grains. They include thin films of translocated clay, coatings of silt, calcite crystals, opaline silica and many other substances.

Detrital Grains- A unit composed of a single mineral grain of any size, derived from the parent material.

Faecal Material- The faecal material from various soil organims varies widely in shape and composition and can vary with the same animal depending upon diet and the natrue of the material when deposited.

Fine Material- The mineral and/or organic material <2µm that is not easily resolved with the petrographic microscope. The fine material composed of clay and/or humus is usually responsible for the soil color.

Impregnated Surfaces- These occur at the surfaces of peds or pores and have a similar fabric to the innermost material but have a different color which usually ranges from yello through brown to black due to the addition of material or the oxidation of compounds of iron and manganese.

Infillings and Intergrowths- Features such as coatings and crystal clusters may occur partially or completely surrounded by the matrix or some other feature. This gives the appearance that they are filling pre-existing spaces and are therefore regarded as infillings.

Microorganisms- Most are too small to be seen in thin section. However, some fungi can be made visible with suitable stains.

Organic Materials- Mainly orgainc ltter and its decomposition products in surface horizons, and roots in deeper horizons. Opal phytoliths may be considered a decomposition product as may the fungal mycelium and small decomposers.

Particle Size Distribution- Although difficult to determine, rough calculations can be made. Easiest to estimate by comparison with standards.

Passages- Faunal and Root - Orgnisms such as earthworms, termites and beetle larvae that burrow through the soil create passages (channels) and chambers which in cross section are usually circular or ovoid with smooth surfaces. Plant roots also form passages of similar shape that may become filled with soil material after the plant dies. Burrowing animals excavate a passage whereas plant roots force their way through the soil as their diamter increases thus creating pressure within the soil.

Rock Fragments- FitzPatrick defines them as a unit of any size containing two or more individual minerals with the same arrangement as when it was part of a rock mass. These may include fragments from which the soil was developed as well as other fragments incorporated into the sediment. These are alos called lithorelicts.

Secondary Mineral Material- It is often difficult to determine whether a given mineral is formed insitu or inherited from the parent material. The ease with which secondary material can be identified is usually determined by the size of teh individual grains.

Segregations and Concretions- Local concentrations of one or more substances in teh soil. Segregations are soft in hand specimens and in thin sections they appear as impregnations of the matrix and are subspherical or irregular in shape with diffuse boundaries. Concretions (also nodules) are hard in hand specimens and occur separately or within thematrix. They are usuall spherical to subspherical in shape but may be irregular with distinctive fabric and/or mineralogy which serve to differentiate them from the rest of teh soil and give them a degree of prominence.

Soil Erratics- A number of sediments and soil horizons contain features that are recognized as once forming as a part of a previous soil. They vary from small aggregates of material to clay coatings. They are common in alluvial and estuarine deposits.

Subsurface Organization and Accumulations- These occur beneath the surface of a ped or pore and spearated from the surface by a layer or band of the general soil material.

Surface Residues- The outer surfaces of aggregates from which one or more constituents have been removed. The two most common types seem to result from the loss of clay and oxides or finely crystalline calcite.

Weathering Features and Products- A wide variety of types and patterns of weathering depending on the nature of teh material and the process involved. This includes chemical and physical weathering.

Other Features- other features to be found in thin sections include shell fragments, diatoms, phytoliths, radiolaria, sponge spicules, and pottery (artifacts).

This page (http://www.ces.ncsu.edu/plymouth/programs/other.html) created by
Vera MacConnell, Research Technician, I on February 6, 1998.
Last Updated on February 6, 1998.