Cob Re.cob fireplace

[Rog]

> I have thought of using some of the large rocks that are located near 
> here. I think cob and rock go together quite well, but I have used 
> some in fire pits and had some crack. Might be a good idea to try 
> them in a fire first and let the ones that crack, crack and use the 
> rest.

Testing the rocks sounds like a good idea.  You may also want to avoid
certain kinds of rocks, too.  I'm going _way_ back into my memory here, but
I remember my father (who's a bit of a geologist given the moment) talking
about some rocks with air or water pockets inside them (presumably volcanic
rocks) which become heated when used in fireplaces and consequently
explode.  Sometimes this is just a dull crack, other times it's much more
impressive (or not, if it's in your fireplace).
But then, maybe my father was just yarning away a bit?

Cheers, Rog.