The major micromorphic classification schemes that follow place a great deal of emphasis on the organization of the clay fraction. Individual clay minerals are usually too small to be resolved in the optical microscope, let alone to be able to distinguish their optical properties. It is our good fortune that clay mineral sseldom occur as descrete entities randomly dispersed throughout the soil matrix. Clay minerals often occur as domains, aggregates, pore linings or infillings, coatings around stable grains, bridges between grains, and various patterns of preferred orientationl. Because clay minerals may concentrate or be reoriented with internal parallel oriented domains in a specific direction, their combined presence forms large enough bodies to be observed and optical properties discerned.
Domains consist of two or more clay particles acting as a unit, usually in parallel orientation.
When domains within clusters are in parallel orientation they form units large enough to observe through the microscope. Thus, small flecks of clay are usually domains while larger optical features of clay may be described as cluster. On page 19 is a brief schematic of the orientation of clays into larger structural units. The domains may either be in random or parallel orientation. Prallel orientation of domains would result in a number of possible striated b-fabrics.