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Identifying composition of raw clay

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Hello, im sorry if there is already a post for this but i did not see any in my searches, I live right in the big bend of the mississippi river on the iowa side in davenport, ia. now just across the river in illinois at a park with great cliffs exposing a ton of bedrock there is this black shale like clay layer. ive refined this down, and the black shale just breaks down into grey clay given the time and agitation in water. ive done a few modeling tests with my early small batches, and it air dries with no cracks smooth silky surface on small little objects. (see attatched photos. ive got some bigger batches ready to "play" with and im going to start going for real pots and bowls and what have you, then im going to use a charcoal grill to do some firing tests *ill be building a kiln this summer* im really new to all this, and been enjoying this more then i can explain, but alas im a bit of a nerd. so i like to know the technical little things down to the composition of this clay. ive researched, and watched a million videos on youtube. ive tried making sense of the geological information i could find online. and i think that i found a type of illite clay? but id really love to know if theres a way i can actually figure this out, that doesnt require taking a geological class so i can make sense of the surveys.  any information would be greatly appreciated!


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State geological survey map of the area is probably the best bet to get an idea of what could be in your found clay. As far as a more precise composition profile you can get a sample(s) analysis done. Forum member @GreyBird had this done, you could pm her and ask about cost etc. There is a fair bit of info on her work with found clay in this thread.  If you had a kiln I would suggest firing a sample up to bisque temperatures,  you won't be able to reach those temps with a charcoal grill.

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yeah based on state geological its likely illite with a high alumin content. but the blackness of the shale suggests a high carbon content as it is NOT magnetic.  but thanks for the info, just so much to learn!

i should also add i intend to keep this process as primitive as possible, what got me into pottery is the fact that in order to make a good forge, i must be able to make good bricks. and so this is where my learning path has found me, im going to make a "cob" kiln to make bricks to make a real kiln, from there i can make better quality bricks and crucibles for my forge. but i always loved working with clay when i was young, and it would be a shame to just get bricks down and move to forging, id like to have some fun in pottery and maybe ceramics if i can get a successful kiln made up, i live in an area rich in coal. so a fuel source will be no problem for me either!

Edited by bringr0fst0rms
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