With a higher proportion of sand, water flows quickly washing out nutrients so sandy soil tends to be poorer. The water content is a factor in soil temperature so clay soils tend to warm up more slowly. Rubbing a small sample between finger and thumb will give a rough guide to the texture of soil. The amount of organic matter and calcium in the soil can change the feel, chalk can give a silky or gritty feel and organic matter makes it more sticky. The distribution of the particles determines the structure of the soil and how porous it is, it is important to maintain a good structure.
Compaction reduces the porosity, the addition of grit and organic matter increases it.
Wetting and drying, freezing and thawing, root growth, soil organisms and cultivation are all actions which change the structure. Sand or silt particles do not aggregate well and tend to fall apart when wet, clay particles adhere better so their presence increases the stability of soil structure. The addition of humus, chalk and iron oxides bind the particles together, forming small clumps or crumbs but clay particles are the main stabilizers in a good loam. The top 50mm of soil should have a good 'tilth' with stable crumbs of 0.5mm to 5mm. Wetting and drying can cause a breakdown of the tilth to a fine dust which dries to a cap or pan, subsequent watering fails to penetrate and seeds cannot break through.