What is soil made of.

[Devil's advocate]

Sounds simple till you think about it.

I started thinking about this when a guy asked me what clay was made of and why his was blue & my clay was yellow.

I did explain that blue clay is waterlogged yellow clay but he seemed to doubt me & asked why?

So I resorted to the internet

To find the most common basic element in a clay soil answer is SILICA
The most common element in sandy soil is SILICA
right I'm really confused now,
can some one explain why the two soils are so different if the basic element is the same

Going back to clay
Clay is usually combined with iron & it goes rusty so you get the yellow clay. When there is no oxygen it turns blue.
White clay contains no or very little iron, it will usually contain Aluminium ie bauxite is a white clay.

 

[Kiwi Pete]

Interesting.
The only definitive thing that is different is particle size (we have silt, which is more like a clay, in how it behaves) and it is really the size of the particles, and thus how they react and relate to the other things (water, air, nutrients) that make a difference to the properties of each individual soil: try making teacups with sand.

And that's largely it - the size difference between a clay particle and a grain of sand is relatively immense, compared to the other things that are in there, like the pores, the water and the living things..

So although the parent material is the same stuff they are nothing alike; a pine forest and a piece of paper are both made of wood, but it is much easier to write on the paper with a ballpoint pen!

 

[B'o'B]

Interesting.
The only definitive thing that is different is particle size (we have silt, which is more like a clay, in how it behaves) and it is really the size of the particles, and thus how they react and relate to the other things (water, air, nutrients) that make a difference to the properties of each individual soil: try making teacups with sand.

And that's largely it - the size difference between a clay particle and a grain of sand is relatively immense, compared to the other things that are in there, like the pores, the water and the living things..

So although the parent material is the same stuff they are nothing alike; a pine forest and a piece of paper are both made of wood, but it is much easier to write on the paper with a ballpoint pen!

Also levels of impurities can have large effects on the soil properties.
A bit like changing iron to steel by adding carbon, or changing steel to stainless steal by adding chromium.

 

[ollie989898]

As you have already outlined, clay is actually very very tiny particles of silica compounds (there are dozens of these) that assemble themselves in peculiar ways, which is what gives clay it's unusual properties, they also tend to contain and trap water in them.

The colours are down to the silica compounds involved and what other impurities are trapped in it. I can't remember the ones responsible for blue or yellow colours any longer.

Soils tend to have an inorganic fraction (Ie very small rocks) and an organic fraction, with varying proportions of the two. A pure clay will have virtually no organic component, whereas a peat is virtually all organic material.

It is weird to think that there is no chemical difference between a sand and a clay, only the particles are different shapes and so fit together differently.

 

[Kevtherev]

Look at your bedrock that’s usually what soils are derived from in your locality or alluvial/glacial deposits.

 

[Kevtherev]

 

[Spencer]

I always thought the largest property in soil is Micro organisms.. albeit probably not by weight..

 

[Devil's advocate]

Look at your bedrock that’s usually what soils are derived from in your locality or alluvial/glacial deposits.

Yes not too hard here, tends to be sandstone or clay (with layers of a very soft flat stone)

I was amazed visiting local stone quarry (just across the road) that their was the top soil, sandy subsoil, then 26 foot of Yorkshire sandstone underneath that it was solid clay suitable for making clay pipes.

So throughout the area the same stone & clay exist just in different layers. Of course in drystone wall country it is always interesting to look at the different types of stone in the walls.

Would be interesting to have a geologist explain how the layers are so mixed.

 

[Kevtherev]

Yes not too hard here, tends to be sandstone or clay (with layers of a very soft flat stone)

I was amazed visiting local stone quarry (just across the road) that their was the top soil, sandy subsoil, then 26 foot of Yorkshire sandstone underneath that it was solid clay suitable for making clay pipes.

So throughout the area the same stone & clay exist just in different layers. Of course in drystone wall country it is always interesting to look at the different types of stone in the walls.

Would be interesting to have a geologist explain how the layers are so mixed.

I think it’s to do with either glaciers or when the earths ‘plates’ moved heaving up the layers.

 

[glasshouse]

The clay must have been a lake or sea bed, then the sand got dumped on top.
I reckon a huge tidal wave hit the east coast of scotland and dumped loads of blue clay where it shouldnt be

 

[Jetemp]

I’ll add a few bits! Air & water!

 

[Devil's advocate]

Yes glaciers & movement of tentropic plates (sorry about spelling) causes the different layers. One side of a hill clay soil the other side yorkshire grit etc.

But if both sand & clay are silica based & this is all new to me. Surely at some point in the evolution of the planet the particles of silica must have been exposed to great heat or great pressure.

It is the opposite of what it seems but clay is very tiny particles which stick together, wheras the lightest sands are actually coarse & rougth in texture if looked at with a microscope.

I think both diamonds & coal are carbon based but the atomic structure is different ie coal in layers which slide off easily, diamonds in a hard grid like structure.

Yet when the soil erodes into the sea it seems to become sand you never see clay washed up on the beach, I suppose it must sink.

I'm giving myself a headache but why do we have potash, boron & salt mines. Surely they should be all mixed up together if they originate from the bottom of the sea.

 

[dowcow]

Why so much variation in little distances: During times of glaciation, or even with no glaciers and just rainfall, various channels where water would flow would sometimes be blocked and would find another path. The different layers of sand and clay would be dropped out of flowing water at different speeds of water flow. Ie. fast flowing water would leave pebbles behind but move the sand, which would be deposited where the river opens up and slows down. Where sand is deposited, finer silt would still be moved downstream, and this would be deposited there.

I think at various times our land has been covered by glacier, river/lake, sand marsh, beach and estuary and centuries of farming has resulted in a damn good top soil to 9-12inches deep mostly. There's a sand/gravel layer an inch thick further down in some places too. I am told to the west of us this gets thicker, and the the east thinner.

 

[Paul Gosling]

There is a huge difference between clay and other fractions of soil. Clays have been chemcially weathered from the parent rock, there are different clays with different properties, depending on what the parent rock type was. So some are chemically relatively inert and contain few nutrient elements and others are much more reactive and contain a lot of nutrients. Clay particles also have electrochemical charge, so can 'hold on' to nutrients (and other ions). Different clays also shrink and swell to differing degrees in response to wetting and drying. Sand and silt are just size fractions, sand is often quartz and other hard minerals and pretty enert. Silt can be all sorts of minerals.

 

[Bogweevil]

Yes glaciers & movement of tentropic plates (sorry about spelling) causes the different layers'....m giving myself a headache but why do we have potash, boron & salt mines. Surely they should be all mixed up together if they originate from the bottom of the sea.

Potash mines are the remnants of dried up seas but because potassium and sodium chloride and indeed all of salts, but especially magnesium chloride, have different solubility they precipitate out to form layers rich in potash (still plenty of salt in potash mines though).

 

[Macsky]

http://theskyetimes.co.uk/index.php/3901-martian-soil-strikingly-similar-to-skye-s

 

[Bogweevil]

The landscaping trade uses artificial soils; 10% composted municipal waste, 90% minerals, usually quarry overburden ground and screened to make a 'sandy loam'. It seems to work well enough.

British Sugar compound a superior material from beet washing, but it costs more.