Silt or clay ? (with pictures)

Hi Guys

Recking my head over the Soil Jar Test.

I took soil samples from a Ricefield a week ago (@ 20cm (right) and @ 2m (left)

Now the 2m sample seems to have a thin layer of clay sitting on top, whereas the 20cm sample doesnt seem to have any, although i gave both jars the same amount of earth, the 20cm is retaining the water alot better which would indicate clay as far as i know.

Another few mysteries:

- Water has  cleared fully on the 20cm sample, but innitially was dirty until about a day ago.
- Water in 2m sample is still clearing but it was quicker to start clearing up.
- The second layer in both jars (I presume Silt ??) is indentical in colour and seems to be the same type of soil, but why has one absorbed a greater amount of water while the other actually seems to have a higher clay content ?

Anyways im excitingly confused, hopefully somebody with a great eye for these things can help me out ?

I have laid out every layer over newspapers to let it dry for a while so i will be posting a few more conclusions (or questions ) in time.

Two ideas for tests:
1)  take the settled out layer, and rub against your teeth. if it feels gritty, it's silt, if it feels smooth, it's clay.
2) Take the layer out, and allow it to dry until it's not liquid. Roll it in your fingers. Does it quicky lose water and start to crack? Silt. If you make a ball, cup it in your hand, then tap it, does water rise to the surface? Silt. Does it keep the water, and allow you to roll out a long snake about pencil width? Clay.

You can do the same sort of informal tests with damp normal soil, just pulled out of a hole. Even 2-5% clay will have a noticeable impact on soil consistency/cohesion and how quickly soil dries in your hands.

Assuming you haven't touched them, the fact that stuff is still suspended in water after a week does point heavily to clay.

Hi there thanks for the advice

I laid them out to dry and its seems that the sample with visible bit of clay is not as strong as the sample with no visible clay.

All the signs of clay but no actual layer of it to be seen ? It holds up good against all the test, but im not sure i could build a cob house with it without being sure what the actual ratios are ...

Anybody had this experience before ?

As Catie said, do these tests ... the nerves in your mouth will feel silt grains, but not clay. T
here is virtually no way of "seeing" if a layer is clay or silt, as the grains are too small for your eye to see (contrary to sand, which grains you see very well). But the differences the clay has on soil cohesion and water retention capacity are enormous.

Padraig - I'm afraid I'm not familiar with what percentage clay/sand etc, you are looking for for cob. Do you have any soil remaining that you haven't done jar tests with?

If you tell me what percentages you are looking for, i can try to explain how that kind of soil is "supposed" to feel - in my field work, I'm usually only 5-10% off from my estimates to lab results. Unfortunately, soil classification is one of those things that's really easy to explain and get a feel for in person, but really hard to teach over the internet!

If you are in doubt about if it's suitable for cob - my other suggestion would be to just build a test block with different percentages of straw, let it dry, and see how it performs. Clay and silt physical properties can vary so dramatically from location to location that it's probably the only way to reliably see how something will perform.