Pottery of natural stone?

[shaggybfc]

I found this earlier in the year - Before Covid. I wasn’t sure if it was natural stone or something man made. Looks rim shaped and has inclusions but is very hard, stone-like.
From the South Warwickshire area.
Any thoughts?

[Pottery Man]

It is a really tricky piece because it is only the remains of a sherd. The petrology is not my field. I can see a lot of alluvial grit and the fired pot was hard-fired inside a bonfire in a shallow pit, hence pit-fired. It was slowly heated to avoid boiling out the chemical water within the clay (thats what bursts a clay pot - heating too fast, too soon) and the firing is controlled by smoke. Excess smoke in your bonfire slows down the heat rise. That smoke sometimes seals in a certain amount of carbon (soot) and once the heat begins to change the clay into irreversible pot at about 750 degrees, the smoke will cause reduction of the iron oxide from red to black. This is black throughout and has not evidence of red or brown clay. It was fired to over 950 and then buried under soil or sand or turf to allow it to cool slowly.
When?
Bronze Age & Iron Age sherds can be found like this, but hard-firing of coarse gravel-tempered clays also occurred after the Romans left. Nevertheless, I favour early to mid Iron Age, but we really need a better sample or an archaeologist handling just that mix of fired clay. It has a signature of grits that has not turned up with myself or my immediate colleagues recently!
"Its a piece of 500BC coarseware....mmh, maybe."
"No its more like a late Bronze cremation urn, but it has no surface left on it...."
"You can't be sure: its too rough. Tell him to go and look for more!"

Sorry bud! That's the way they are. They said other things, too.
It is interesting and they were willing to look!