clay cooking stones?

[karie]

I have a few ideas what these may be but honestly i need help figuring it out...the look like a clay material but they sound like a rock would when they clack against eachother they also apear as though they had been in direct contact with fire so...i would love to get some input.

[SDhunter]

I really can't tell if they are clay, but if not, then they look like concretions to me.

[rmartin]

I agree. They look like natural concretions.