PEDOFEATURES: (different concept than Brewer's "Pedological Features) They are discrete fabric units present in soil materials recognizable from an adjacent material by a difference in concentration in one or more components (organic matter, crystals, chemical components, or by a difference in internal fabric). It is important to note that birefringence fabrics are excluded from consideration as pedofeatures. There is no upper size limit for pedofeatures though if the feature is continuous across a thin section, e.g. placic horizon, or covers the whole of the section.

Before describing pedofeatures, it is necessary to identify the different types of pedofeatures in the thin section. Description is made of each type on either the whole population or a typical example which is later compared to the whole population. Description is according to the following order:

1. Nature of Pedofeature;
2. Size (See chapter 4);
3. External Morphology, including sharpness of boundary and surface roughness;
4. Internal Fabric, which is closely related to their nature;
5. Contrast with Adjacent Material;
6. Abundance of pedofeature;
7. Variability or degree of similarity between features of the same type;
8. Basic, referred and related distribution and orientation patterns.

Pedofeatures Related to Voids, Grains and Aggregates: These features can occur directly on the surface, immediately adjoining rather than on the surface or somewhere in the matrix but with a surface relationship (see table on next page)

Coatings: These are pedofeatures that coat the surfaces of voids, grains and aggregates (cutan of Brewer). Coated grains and aggregates can be embedded in the groundmass but the concept of coating excludes birefringence fabrics.

Hypo-coatings: These occur immediately adjoining rather than on the surface with which they are associated (neo-cutan of Brewer). they may arise by impregnation of a groundmass immediately adjacent to the surface (external hypo-coating), by impregnation of the surface zones of microporous grains (internal hypo-coating) or by depletion of a component as is depletion pedofeatures.

Quasi-coating: These are related to surfaces of voids, grains and aggregates but not immediately adjoining them (neo- and quasi- cutans of Brewer).

Typic: Applies to all three forms of coatings when they are approximately regular in thickness throughout their length.

Crescent: A coating, very rarely a hypo- or quasi- coating, with an elongate concentric shape.

Capping: A coating lying on the top of rree or embedded grains or aggregates. Link capping: A capping that covers the top surface of, and is supported by, two or more rains or aggregates. The shape and thickness of the capping are variable. Cappings can be restricted to the tops of grains or aggregates but more frequently envelop lateral edges also.

Pendants: A coating, rarely a hypo-coating and very rarely a quasi-coating, on the lower face of free or embedded grains or aggregates. Also a field term.
Micropan: A thick (>0.5mm) coating occurring horizontally at some level within the soil, varifying significantly in thickness over its length.
Crust: A thick (>1mm) coating present on the soil surface. The term applies to discontinuous features. When continuous, it is described as a layer or horizon.
Infillings: These are formed of soil material, or some fraction of it, infilling or partially infilling voids. To be classed as infillings rather than coatings, the void must be more than 90% filled. this limit applies only to dense infillins; loose infillings never coat voids. The concept of infillings is broader than that of pedotubules (Brewer), the latter being restricted to tubular voids and to textural, fabric and excremental material.

Dense complete: the void is completely infilled.
Dense incomplete: The infilling is continuous but some voids are present.
Loose continuous: The infilling consists of grains, aggregates, crystals or excrements, irregularly distributed, or in clusters.

Pedofeatures Unrelated to Voids, Grains and Aggregates (see table above)

Crystals and Crystal INtergrowths: These are pedofeatures formed in situ, which consist of a single crystal and/or crystal intergrowths, normally >20µm in diameter, embedded in the groundmass.

Nodules: These are pedofeatures unrelated to voids or surfaces of grains or aggregates that do not consist of single crystals or crystal intergrowths. Similar to glaebules of Brewer. They are subdivided according to internal morphology:

Typic: Equant to prolate nodules with an undifferentiated internal fabric and regular, sharp external boundaries.
Concentric: Nodules with a concentric fabric consisting of more than one ring and approximately circular in shape. Fabric may be cross-oriented. Equivalent to concretions of Brewer.
Nucleic: Nodules with a foreign core such as rock fragment or another nodule. They have an approximate circular shape.
Geodic: Nodules with a hollow interior, often with a drusy lining of crystals (pedode of Brewer).
Septaric: Nodules with a radiating crack pattern. Broader in concept than septaria of Brewer.
Pseudomorphic: Nodules with a variety of internal fabrics depending on the nature of the host material.
Halo: Nodules with a crystalline or strongly impregnative core and a weaker impregnative cortex. The boundary with the groundmass in which the nodules are embedded is usually diffuse. Equivalent to glaebular holo of Brewer.

All the above nodules can be differentiated on the basis of external morphology into:

Amiboidal: Nodules with a contorted shpae. In cases where the nodule appears under the optical microscope to be composed of amorphous material, the term 'mottle' e.g. feruginous mottle, is used to relate to field observation and description.
Digitate: Nodules in which the adjacent material penetrates towards their center more or less like fingers.
Disjointed: Nodules formed of several smaller entities each separated by adjacent groundmass. The entities are more or less angular and accommodate each other.
Aggregate: Nodules formed of several more or less rounded entities that do not accommodate each other.
Compound: Individual nodules consist of two or more of the above types.

This page (http://www.ces.ncsu.edu/plymouth/programs/pedofeatures.html) created by
Vera MacConnell, Research Technician, I on February 5, 1998.
Last Updated on February 5, 1998.