Recently I have read that akadama is mined in Japan. And that there are grades in hardiness in Akadama. While both of these facts are true Here's the rest of the story.....
one source says this: Akadama is natural -- that the harder akadama is mined farther -- deeper in the mine.
Another source says: After the akadama is mined -- they fire it for its hardiness. such as "Hard akadama is high-fired in kilns at 2,200 degrees F and is basically like ground-up brick."
I don't believe everything I read on the internet. Are both sources correct? If not which one is correct? Or is it a mystery!