Shattered Pastry Board
When my grand daughter was ten we were riding our horses on land where the settlers on the Oregon Trail had passed. It was blow sand with lava ridges. As we cut through a particular rough gap I commented, "what if a wagon team spooked here, I'll bet something got broke."
We started looking on the ground and sure enough there were some white shards mostly covered by blowing sand. We stopped and gathered about eight pieces about as big as a dollar bill or smaller and recently I sent them to an expert in pioneer ceramics in NY state.
He said it was a pastry board. It was flat. I thought it was a butter crock but he said that would have had more curve to it.