Your soil was probably formed thousands or even millions of years ago. Usually running water decomposed rocks. As it slowed down when it entered the sea or a lake or a flat area the largest particles like gravel were deposited first. Then sand, then silt, and finally the smallest particles, clay. Various floods could have caused different types of sediment to form layers, so you might have a layer of sand covered by a layer of clay or vice-versa. Then as earthquakes raised and lowered the ground these layer could have become distorted, thats why one part of your town might have clay soil and another part sand. Wind could have also caused deposits of different types of soil to be deposited in different areas.

I never did get into the geology. I skipped over that course in junior high.

"...Today such clay minerals form in soil when organisms such as microbes or fungi interact with tiny bits of weathered rock. The resultant clay then washes down to the sea and settles on the bottom,"

this is interesting from this site

still rather confused

I just now found this info

"Depending on temperature and rainfall, new minerals are formed. The oxides of iron and alumina combine with silica to form clay." from this site

So I guess both clay and sand are both formed from rock. And is the weathering makes the difference.

I could see how compost would wash out of a sand.

Your native soil was formed eons ago from the rocks you have in your area. Clay soil particles are very small and of uniform size and shape and that allows them to fit tightly together. Silt soil particles are a little larger and a little more irregular in shape, but they also fit prettyy well together and neither clay nor silt allow water to easily flow through them. Sand soil particels are quite large in comparison and when pile together have very large pore spaces between them that allows water to flow quite freely.
The lava sand you added to your clay was simply not enough to make any significant difference. You would need about 45 percent sand by volume (Cornell says 75 percent) to make enough change to make much difference. The sand particles push the clay particles apart, the same thing organic matter does except the organic matter adds nutrients that the sand will not.
The sand near that stream was moved there by the water over time. Go upstream until you find the sand source.

Sand and clay are both formed from the weathering of rocks, but NOT FROM THE SAME ROCKS. The parent material of the rock determines whether it will end up as clay or sand as it is subjected to the chemicals and forces of nature. Al

If you have it in the soil- then it's in the soil. It's not going to "form" in your soil by erosion on a timescale that you can use (unless you live for thousands of years).

You can't really encourage formation of one or another in a useful way.

That makes sense about the sand migrating.

I should have said, was: what makes the soil that is formed by weathering, become clay or sand? or what is the process that determines if a raw material becomes clay or sand? It is a hard question to phrase. I did not think clay and sand came from soil or humus. I wanted to know the exact process that lead raw materials to to turn into clay or sand. I read it had something to do with heat, compression, rain and stuff along that nature. I also know it takes a long long long long time, not something that I can create in my lifetime. I was just curious about the process, not wanting to duplicate it.

I don't really think the lava sand turned to clay per say. Mostly thinking out loud. It sure does feel like a clay like substance. I was curious why in such a short time it seems so different. Maybe wet lava sand feels different, like wet sand would feel different than dry sand. I don't think lava sand is true sand anyway, more like ground up rock. In a way that is what sand is, but a different rock. I did not add lava sand to make the land more sandy, that would take a lot of sand! Plus they say sand and clay can make concrete. I added it because I read that lava sand has lots of minerals. But I have since learned, that they mostly sell lava sand to get rid of a waste material from the lava rock industry. I read that our soil, is only low in organic material, not minerals. So adding more minerals is a waste.

I think what is happening under the tree that 'seems' to have sandy soil is, like californian said; the clay has washed away due to the soil having no grass or weeds there. It is also possible the park has the same thing happening. It seems whenever I dig, I see the same sandy type substance under the clay layer, then caliche. I am not good at identifying clay, sand, silt, and loam, but this is the way it appears to me.

Thanks for all of your comments. I have learned from them. I was having a hard time putting it together. I guess it does not matter how sand and clay formed thousands of years ago. I was just curious.

I know that it is futile to try to change the structure of ones native soil. We should try to find out what grows best in what ever soil we are blessed with, and grow that. I read if you truly want to grow something not suited to your soil type, is is best to not amend but to have a raised bed with the kind of soil that you need just added to the top, not incorporated with existing soil. I am not trying to change the structure of my soil, I was just trying to make it more fertile. Does that make more sense now? I just don't want you think I am on the dumb side.

This is an interesting discussion, please continue it.

You can truck in materials that will alter your soil structure significantly.

Clay is composed of very fine plate-like particles. Here's a simple way to imagine how clay works: Think about 2 pieces of glass. Spray one with water and stick them together- they adhere pretty darned well! Now- millions of tiny pieces of glass have very similar properties and they create that clay adhesive property that allows you to use it as a plastic substance. In reality there are a number of charge (static-like) firces that create the adhesive properties, and they will be dependent on the starting material, the fragment sizes, alignment, water content, and other factors.

Sand normally has a crystaline structure that allows for certain stable geometries of particles. Clay is generally more interesting from this perspective (IMO) because it is the product of weather and excessive grinding of the starting material which may produce a wide variety of adhesive forces. Clay is not just clay- if you get me- but I may think this way because I'm a potter on the side.

Here is a link that might be useful: soil/sand/clay

You can find places where soil is being formed as we speak, and see the process in action. You would have to visit a seashore or lake shore with large rocks, or exposed rock outcropping. The rock will have cracks and fissures, and the larger cracks and fissures will have trapped a small amount of soil. That soil would have been formed recently, or fairly recently. There will be plants growing in the fissures. On Isle Royale, a national park located in Lake Superior, there are extensive rock outcroppings on the south shore, east of Snug Harbor. Tiny strawberry plants live in the cracks, and manage to survive there, even though there is only a fraction of an inch of soil. Some of the exposed rock is covered with lichen-there are said to be 200 varieties of lichen on the island. I think the lichens speed up the process of soil formation, but even without them, the rock would very slowly break down due to weathering.

I think a little of the confusion here comes from the formation of clay from rocks and minerals. Sand and silt are essentially just small and smaller pieces of rocks and minerals. Typically sand is primarily quartz which resists weathering. Clays are not just small pieces of the parent material like sand and silt. Clays are entirely new minerals that formed primarily from aluminum and silica. The aluminum and silica comes from the chemical weathering of rocks and other minerals. What type of clay forms depends on what the original rocks and minerals were and the conditions under which they weathered and the clays formed.

Don't forget depositional environments that created the regional rock that contributes to soil formation over time, such as transgressions and regressions of the sea over millions of years. Central Kentucky is karst (limestone) because millions of years ago it was a deep, large ocean. Characteristically water would be calmer in the deep sea for small particles of sediment to deposit versus at a waterfall where the coarser-grained rocks and sediment would deposit first. Deep ocean = finer-grained particles settling down (clays). rough water= course-grained, larger sediment (sand). Our soils in central KY are very clayey and many trilobytes and brachiopod fossils can easily be found in outcroppings of limestone/shale along the interstates. What happens in a transgression is the sea moves to the direction of inland so what was once a rough-water section of sea with larger coarser rocks now becomes calmer, so the lighter fine-grained particles deposit there. This is one method that layers of different compositional subsurface form. In a regression, the sea gives up more land, so what was calm is allowed to be intruded upon by rougher water so larger coarser deposits can be deposited there allowing for sand over clay so-to-speak. Considering the other earth processes mentioned by californian, transgressions and regressions of the sea are another way for the diversification of land. There's also tectonic plates shifting around and sublimation at the subduction zone (Pacific seafloor being dragged under California) for the Earth to keep renewing itself and mixing itself up. This thread is pulling out knowledge I hadn't used since graduating with my degree back in 2000. It's too bad information technology paid better after I graduated cause I really do love this stuff.

Hopefully this provides more background for the ingredients for either a clay or sandy soil to form.

Talk about simplistic, here is a simplistic analogy I once read regarding adding sand to clay.

Imagine clay is a small flat particle like rolled oats.
Imagine sand is much larger, somewhat round like a beach ball.

Now imagine a whole room full of flat, rolled oats all laying on top of each other, compacted. Now add some beach balls.

How many beach balls does it take to break up the oats so that they don't lay compacted against each other?

So I don't wonder that Cornell says 75% sand.

Concerning clay particles sticking together due to static-like forces, people add compost to their clay to loosen it.
I have read that what happens is that the humic acid from the compost neutralizes the static charges holding the particles together, allowing spaces between the particles so that water can drain through.

Here in SoCal I have clay soil so pure that you can fire it in a kiln and make a pot and not just a few lumps of clay in the dirt, there is no dirt, only clay. In my raised garden I tilled in large amounts of mushroom compost and sand with my native soil, probably 1/3, 1/3, 1/3. It took a lot of tilling to pull the clay apart and up into the ammendments. But now a few years later you would never know that the soil in this bed has any clay at all. So you can change your native soil into something else.

Gary

Lakedallasmary - I think you will find that you may have to change your no till philosophy if you have heavy clay.

It would take tilling in lots and lots of material to amend a hard clay soil into something that one would consider garden soil.

Most people with really nasty clay soil construct raised beds with good soil or they till in lots of organic material (ie. Gary's post).

And when it comes to landscape plants (non-veggie-garden plants), you may want to focus growing native plants to your area. Plants that are already adapted to growing in the soil and moisture conditions that exist in your region. Growing native plants minimizes the inputs and work required to grow plants in poor soils.

Here is a link that might be useful: Texas Native Plant Society

Hi LakeDallasMary, I don't like tilling either, and also have a heavy clay soil, although probably quite different from yours. I make lots of raised beds. And although I am a no-tiller for the most part, don't feel that it is a garden sin or you absolutely can't do it. Nothing wrong with putting wood chips into the soil per se.

I make raised beds, layers something like this from the bottom up: cardboard, old produce, leaves, horse manure, old produce, leaves, a little soil or finished compost on top. Our soil runs to the acidic side, so I fling in a small amount of wood ashes as well. (I heat my house with wood.) Viola', excellent soil to garden in. No tilling, and over time the clay underneath mixes with the organic material on top due to worms, roots, and weather.

Your soil isn't hopeless. It just needs a LOT of organic material added to it. Use whatever you can find, grass clippings, other people's bagged leaves, manure, compost, etc. I haven't hit up Starbucks for used coffee grounds, but supposedly those are easy to come by.

Marcia

Lots of good replies here.

In a nutshell: Sand is weathered rock. Tiny little pieces of rock, broken down by wind and rain and erosion.

Silt is weathered sand.

These are primary minerals, broken down rock.

Clay is different. Clay is a secondary mineral, created from the chemicals given off by sand and silt as they break down into smaller particles through exposure to acids like acid rain or organic acids. Clay particles are tiny plates that fit together very tightly and are attracted to each other by electrostatic charges.

Time is the main difference. It takes longer for clay to form than either of the others.

Sand, silt and clay are moved around by wind, water and ice. Vermont is rocky because it was scraped bare by glaciers and has not had time yet to develop new soil. Same thing where I am, in the Puget Sound area which was carved out by glaciers. Our soil is what the glaciers dumped as they melted off after carving out Puget Sound and the Strait of Georgia and Hood Canal. It's like gardening in aquarium gravel. Rocks, gravel and sand. No organic matter. I wish I had clay. The river valleys have really nice loamy soil, because they get what's washing down off the mountains - organic matter from the forests, clay from weathering, volcanic ash off Mt Rainier and Mt St Helens etc, and not least, thousands of dead salmon every fall. Migrating salmon returning from the oceans, going up the rivers, spawning and dying and washing up on the banks. The best fertilizer on earth.

Prairie soils develop when thick grasses trap wind blown silt and clay. A nice loamy mix of organic matter and soil.

Clay soil is what it is. Best to learn to work with it, not against it. You can't change it, only replace it in small areas. Organic matter disappears because the soil microbes eat it. The sand disappears because it gets lost in the clay matrix and sets like concrete.

Clay soil is much more fertile than what I have. Clay particles have a very large surface area to volume ratio, so nutrients have lots of surface area to stick to, and stick they do because clay particles are electrostatically charged. In my gravelly soil nutrients wash right through, there's no clay or organic matter for them to stick to. Sand and gravel have no electrostatic charges. All you need to do is add compost and mulch every year. If you have a good worm population they'll work it in. When I had clay I did dig in organic matter whenever planting something not native to the area, and then mulched every year. But if you add a lot of amendments to a hole in clay, you're just creating a clay pot and the plant can drown because water won't drain from the amended soil into the clay. Just add a little bit in a big hole.

I never did get into the geology. I skipped over that course in junior high.

DOH!!!

I like my clay. I was never complaining. I have no till beds, I use mulch to keep soil cooler and it breaks down to a nice humus. My humus level is now four times what it was when I started these beds 2 years ago. Lots of earth worms too.

I am now reading up on the value of deep rooted weeds to help aeration of the soil. I think I will try live weeds this year verses dead mulch to keep things cool. I have a nice patch of them already! He he!! Mulch can create its own problems.

The garden is doing great now that humus has built up. Gardening is great. Most gardeners are nice folks. I love it that most folks are very helpful here on garden web. There are a few bad apples though that seem to enjoy saying nasty things. Not sure why, guess they are having a bad day. We all do from time to time, so we can forgive them right?

Thanks for all your great responses. They pretty much confirmed what I had thought about rocks weathering into clay or sand depending on certain variables.

Now off to build some cowpea trellises before it rains again and again and again...