I had originally posted this to Reddit but the mods removed it and suggested I take it to a rock and minerals subreddit.... which was infuriating. Anyways, this came in a collection of other Mexican arts and pottery. I have not found anything exactly like it online. I actually have a pair of them. I thought it might be for tortillas but it seems small. It's abou 4" across. Any help is appreciated.
Looks like a stone "comal" but its thicker than the ones I know.