Soil to new conditions. Whether these are slow or rapid changes depends on climate, topography and biological activity. The physical properties of soils, in order of decreasing importance for ecosystem services such as crop production, are texture, structure, bulk density, porosity, consistency, temperature, colour and resistivity. Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly "soil aggregates" are created from the soil separates when iron oxides, carbonates, clay, silica and humus, coat particles and cause
Cob (material) an "unburned clay masonry" when used in a structural context. It might also be referred to as an "aggregate" in non-structural contexts, such as a "clay and sand aggregate" or more simply an "organic aggregate," such as where the cob is an insulating filler between post and beam construction. "Cob" is an English term attested to around the year 1600 for an ancient building material that has been used for building since prehistoric times. The etymology of "cob" and "cobbing" is unclear, but in several senses means to "beat" or "strike", which is how cob material is applied to a