Introduction
In the Handbook for Soil Thin Section Description (Bullock et al., 1985) 6 important basic concepts have been introduced. General descriptive criteria are given and quantification of the features observed in thin sections is briefly discussed.
In this lecture I want to introduce the basic concepts and expand on those mentioned in the title, using micromorphological slides to demonstrate the features, their recognition and description. Their interpretation and importance is discussed especially in the application lectures.
In the afternoon exercises it is possible to practice with those concepts and features.

Basic concepts

Soil fabric (definition):
Soil fabric deals with the total organization of a soil, expressed by the spatial arangement of the soil constituents (solid, liquid, and gaseous), their shape, size and frequency, considered from a configurational, functional and genetic viewpoint.

Special attention will be given to recognition and description of b-fabrics (birefringece fabrics) and briefly recognition and description of some fabric pedofeatures will be demonstrated. Thompson will deal with the origin and importance of biological fabric pedofeatures.

Soil structure (definition):
Soil Structure is concerned with the size, shape adn arrangement of primary particles and voids in both aggregated and non- aggregated material and the size, shape adn arrangement of any aggregates present.

Pedal and apedal microstructures will be discussed, with their associated voids. West will detail the importance of various soil microstructures.

Coarse adn fine material (the c/f concept):
The separation of a given soil material in a fine part and a coarse part, each with its characteristic physico-chemical and mechanical properties, which depends on the grain size distribution. No fixed limit is used and the c/f ratio indicates the proportion of the coarse part and the fine part.

Some characteristic c/f ratio's will be domonstrated. In the lectures of West and Nettleton some of these will be interpreted.

Basic conponents:
The simplest units in a thin seciton (e.g. mineral grains, clay particles and plant tissues). The coarser individual particles can be resolved with the optical microscope, the fine material is unresolvable with the optical microscope, but domains of fine material (b-fabrics) can be observed based on their optical properties.

This is treated for the mineral part in Southard's adn Stolt's lecture. The organic components will be part of Thompson's lectures.

Groundmass:
A general term used for the coarse and fine material which forms the base material of the soil. Pedofeatures are generally not included, unless an impregnative pedofeature does not obsure the original groundmass. It is also possible to describe the 'groundmass' of a pedofeature, if described in detail.

The groundmass in some thin sections will be discussed. The organic part will be treated in Thompson's lectures.

Pedofeatures (definition):
Pedofeatures are discrete fabric units present in soil materials recognizable from an adjacent material by a difference in concentration in one or more components or by a differnce in internal fabric, except for birefringence fabrics.

The majority of these pedofeatures and their association with diagnostic horizons will be discussed by Nettleton and Vepraskas.

General descriptive criteria
In the description a number of descriptors can be used. The most common include:

• size
• shape
• frequency
• sorting
• colour
• boundary
• orientation patterns
• distribution patterns

Quantification and characterization
Various techniques exist at present:

• point counting on thin sections (sometimes expert judgemetn/interpretation needed) for features and pores.
• image analysis (black and white - quantification of soil microstructure, especially pores/using Remote Sensing Techniques on digitized thin sections and various colour bands - classify and quantify coloured objects in thin sections)
• SEM-EDXRA (Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis)/ Microprobe for characterizing chemical/mineralogical compostion
• Microdrilling and subsequent SEM-EDXRA/XRD (X Ray Diffraction) - in situ characterizaiton of very small features possible.

This page (http://www.ces.ncsu.edu/plymouth/programs/miedema.html) created by
Vera MacConnell, Research Technician, I on November 3, 1997.
Last Updated on November 3, 1997.