First in an occasional series of definitions
A great deal of this business is about soil, and the wondrous many varieties thereof. To understand the differences, we shall have to dig a bit deeper (sorry) and take a look at some defining characteristics.
In general terms, the solid content of soil is a mixture of mineral particles and organic matter. (There will be air and water in there too, as anybody buying the stuff by weight will tell you.) For this post, let's look at the mineral contents.
The hard, inorganic stuff in soil consists of various kinds of rock, ground down by the action of weather and plant roots over the millennia. Obviously, the type of rock will have an impact on the speed with which the breakdown process progresses, as well as on the ultimate size of the resulting particles and their chemical composition. This is why soil and sand varies from location to location - if the exact specification of your soil is important, then you must look for an analysis of material from your specific source.
Mineral particles are defined by their size and are known as sand if bigger than 0.05mm (and if they are bigger than 2mm, then they are gravel and don't belong in soil at all). Particles smaller than sand but bigger than 0.002mm are called silt, whereas even smaller particles are clay. You can easily feel the difference by touch - clay compacts if you squeeze it, silt feels silky and smooth, while sand feels gritty. The mix of sand,silt and clay will determine how well the soil drains - or retains moisture, depending on how you look at it. The bigger the particles, the more free-draining.
In the next post in this series, we'll take a look at the organic content of soil.