The physical framework of the soil is actually built of inorganic mineral crystals which differ in their size and compose of 45% of the soil’s volume.
These particles are distinguished based on size as sand (0.05 mm- 2mm), silt (0.002mm-0.005 mm), and clay (<0.002 mm). The proportions of these minerals relative to each other give the soil its texture .
A soil triangle is a human invention to be able to classify soils based on their textures.
This can be useful in assessing soil for building applications (mortars, plastering, lining, moulding).
The secretions of the microorganisms, worms and insects, roots and also forces due to chemical/nature of these mineral particles, make them clump together to form aggregates (peds). The nature of arrangement of these aggregates with each other is understood as the structure of the soil.
The size of the aggregates particles determines the space in between two aggregates. These spaces (pores) make up for 50% of the soil’s volume. The larger the aggregate size, the larger the pores between the aggregates.
These pores are occupied either by air or by water.
Lighter soils (larger aggregates/pores) drain rapidly while heavier soils (smaller aggregates/pores) drain slowly. A well drained soil maintains a balance in the distribution of pore spaces for water and air and keeps the supply of oxygen through the air and the nutrients through the water continuous and consistent to the plant roots and soil animal life which form the remaining 5% of the soil’s volume. This is referred to as the organic matter of the soil.
Since it is primarily because of the organic matter that aggregation happens, adding organic matter to the soil, helps improve its structure.
This relationship between a organic/living and an inorganic/non-living creates a sustainable micro-biome, necessary for all land animals (including us) to derive their food from.