If the soil holds together in a firm shape like plasticine, it will be mainly clay. This has the smallest size particles of the three soil types.
Clay soils can be found in varying colours from white and grey through to brown and dark orange-red. This colour range is reliant on the contents of the soil in which it forms.
The major plus for clay soils is that they have a high cation exchange capacity. The plate-like structure gives a large surface area and because clay particles are negatively charged, there is a lot of area to hold the positively charged elements which are the nutrients plants require.
Soil structure can be improved dramatically by adding organic matter and more organic matter. Organic matter such as compost, animal manures and green manure crops together with byproducts produced by microorganisms that break down the organic matter, form clay particles into aggregates. These aggregates are larger clumps of soil particles and have spaces between them where air and water can move freely, plants roots can develop, microorganisms can live.
If the soil holds together reasonably well but is slightly crumbly, it is probably a silty soil. Its soil particle size is somewhere between clay and sandy. Usually found near waterways, having been deposited by slow-flowing water.
If the soil is crumbly and has sand particles throughout, it is a sandy soil. It has the largest particles of the three soil types.
Sandy soils are not very fertile as they have very little to no cation exchange capacity. Sand particles are not charged and therefore unable to hold any nutrients.
Loam soil has the best features of all the soils.