Big D,
I saw something on Turface being a fired clay, additionally, I know the Europeans also use Lecca, an expanded clay product.
Down here if you go to the brick factory, there is a 40 x 40 x 60 foot room filled with crushed brick. It's free and with three friends, in less than an hour with a home-made rocking sieve you have enough to last a few years.
What I didn't know or understand was -
[1] Why didn't anyone just write the Japanese company and ask for a properties sheet for the Akadama used for bonsai ???????
[2] That Akadama is fired at 3 different temperatures.
We have naturally fired clay from underground gas fires [ this island produces oil ] and the clay is not as hard as the brick, but can be brought up to any temperature.
It is also free, you just have to sieve it.
Lastly, we also have a deposit of yellow stone, that is porous, and resists decay, it grows trees exceptionally well.
I guess, I was always curious about Akadama, but stupidly not curious enough to write the Japanese company as well - ha ha - I laugh at my self.
Good Afternoon.
Anthony