Hello everybody
I see that the classic confusion on clay, silt, sand is raising its head once again. Remember for each of these words there are at least 2 or 3 different definitions that overlap.
Clay is 1 word for at least 3 different things. To confuse matters even more the 3 different things overlap somewhat in practice.
Clay 1st definition is a sediment particle that is smaller than 2 micrometer (aka 2 micron or 2µm). This definition is purely based on
grainsize or
granulometry. Any naturally occuring - non organic - soil particle smaller than 2µm is clay 1st by this definition regardless of chemical or mineralogic compostion.
Because of its small particle size, fluids cannot flow easily trough clay (1st).
Clay 2nd definition is a mineral that consists out of Silicon, Oxygen, Aluminum and potentially a whole bunch of other charged particles. IN GENERAL the claycristals (2nd definition) rarely 'grow' larger than 2 micron. Hence the overlap.
Clay (2nd) is often electrically charged over its external surface. That is the base for a lot of the usefull properties of clay. It holds magnesium-, calcium-, iron-, manganese-, copper-ions etc... to neutralise its charge. It also holds hydroxonium (H³O+) so it helps to buffer soilacidity - in other words it can help keep the soil pH neutral despite acid rain and such. The ions (=charged particles) are
adsorbed on the surface.
https://en.wikipedia.org/wiki/Adsorption
Clay (2nd) has a platelike cristal-lattice. Basically the stuff consists of layers of Siliconoxide and Aluminumoxide. In between these layers even more ions can be captured - this are absorbed between the layers. The smaller the ions are, the easier they
absorbed in the internal structure of the clay.
https://en.wikipedia.org/wiki/Absorption_(chemistry)
The absorption is not limited to ions. Clay can also absorp small dipolar molecules like water. Clay minerals that are very good at absorbing water expand their structure. The cristal becomes bigger it swells. Such clayminerals are wel known to permies, builders and petroleumguys alike as
bentonite-type clays.
A dipolar molecule is a molecule that has an uneven distribution of its electromagnetic properties. Such molecules behave as small magnets.
Clay (2nd) is generally also has a platelike shape. It's diameter is far larger than its thickness. That is one of the reasons that clay deposits only in very calm water. Playing with the ion content of the water can have an influence on the speed of sedimentation.
https://en.wikipedia.org/wiki/Flocculation
Clay (2nd) is formed when other minerals weather chemically. There are hundreds of species of clay minerals. The more unstable a mother mineral is on the surface of the earth the more easy and the faster it changes into clay. Volcanic rock is generally fertile because it consists mostly of minerals that are formed between 750°C and 1500°C. The stability of these minerals under surface conditions is low - they weather fast and rapidly form claysoils. Volcanic rock is mostly rich in magnesium, calcium, manganese, iron, etc... So clays forming out of volcanic rock tend to be very fertile.
There is lots to tell on clays - if you want more - this link is a good starting point.
https://pubs.geoscienceworld.org/claymin
Clay 3rd definition is a soil/sediment science definition based on granulometry/grainsize. THIS definiton does not take into account volume of organic material, rock, boulders, etc.....
Clay SOIL (3rd) consist out of a Clay (1st) which may in its turn consist out of Clay (2nd). Mixed in with the Clay (1st) are variable volumes of SILT and SAND.
The exact definition of claysoil is different from country to country - hoera, if possible even more confusion. Clay (3rd) is often defined by way of a 3way diagram. Belgium, the US, the Unesco, etc... all have different definitions of what is clay (3rd) soil.
Whatever the national origin of Clay (3rd) it is generally good to encapsulate and protect organic material and other stuff from oxygen. Hence Skandi's remark about future oil fields. That is also the reason why clay soils are often blueish green to black at depths where sandy soil has a rusty colour. Organic material and Fe²+ are not completely oxidized.
https://en.wikipedia.org/wiki/Soil_texture#/media/File:SoilTextureTriangle.jpg
https://en.wikipedia.org/wiki/Soil_texture
Silt and Sand can also be defined from a granulometric, mineralogic and pedologic point of view. Silt and sand also have different adsorption and absorption properties depending on their mineral content. Hard and hard weathering materials tend to dominate the composition of sand. Such minerals adsorp little and absorp even less. The grainsize is bigger so the pores in between soilparticles are more connected. Liquids can pass easier trough silt and especially sand.
You can capture clay (1st) and clay (2nd) by way of sedimentation but you need to reduce water speed drastically. In a horticultural sense/soil improvement that is almost unheard of in western agriculture. In Egypt, it is being done for thousands of years.
I guess you could do it by building a structure similar to a rice paddy - you bring in sedimentrich (hopefully clayrich) water AKA muddy water trough a narrow, fast flowing canal and then you bring it in a broad, pondlike, flatbottemed bed where you want your clay to sediment. Plants in the bed can help to capture the fine sediments.
With this process you will not harvest pure clay usable for pottery.
I would not recommend this proces for general use in permies. After all - undisturbed soil in situ is almost always the best.
BEWARE Because of the adsorption properties of clay (1st and 2nd)
and the absorption properties clay (2nd) and the tendancy to preserve organic matter in clay (1st and 2nd) ALL KINDS OF POLLUTANTS tend to build up in your sediment. Some of these remain harmfull. Sludge is considered a potential environmental hazard for this reason.